A MAGYAR MITTEILUNGEN TUDOMANYOS AKADEMIA DER CSILLAGVIZSGALO STERNWARTE INTEZETENEK DER UNGARISCHEN AKADEMIE KOZLEMENYEI DER WISSENSCHAFTEN BUDAPEST - SZABADSAGHEGY Nr. 70. L. SZABADOS PHOTOELECTRIC UBV PHOTOMETRY OF NORTHERN CEPHEIDS I. BUDAPEST, 1977. PHOTOELECTRIC UBV PHOTOMETRY OF NORTHERN CEPHEIDS I. ABSTRACT New UBV photoelectric observational data on 38 northern cepheids with periods of less than 5 days are presented. The period changes of the observed cepheids are investigated. Four variables (SU Cyg, DT Cyg, V 532 Cyg, SZ Tau) show a period jump and a subsequent "rejump" to the earlier value of the period, which results in the overall constancy of the period. DT Cyg pulsates with the same period for at least the fourth time which is in keeping with the recent hypothesis on the evolution of cepheids along the lines of constant period in the HRD. AU Peg, a Population II variable, shows extremely strong period changes. In three cases, secular light curve variation was discovered. The amplitude of the light variation of AS Per is decreasing; the other type of light curve variation is the variation in the steepness of the rising branch (SU Cyg, FF Aql). The effect of the orbital motion on the O-C diagram is also investigated for FF Aql. Finally, the instability of the period for different types of cepheids is discussed. INTRODUCTION This paper is the first part of a series dealing with the new UBV photometry of northern cepheids started at the Konkoly Observatory in 1971 and it contains the observational data and O-C diagrams of cepheids with periods of less than 5 days. The following papers in the series will deal with the photometry of northern cepheids with periods greater than 5 days. Observations on about 70 variables are in progress. Although in several respects broad-band UBV photometry cannot compete with observations made using intermediate band systems (e.g. Pel 1976), the UBV system is still the most generally used photometric system so the major part of the observations on cepheids have been made in this way. With this large amount of homogeneous observations it is possible to investigate the cepheids from several different points of view. Nevertheless, the available photoelectric observational material on cepheid variables is not sufficient. Three UBV photoelectric observational series on northern cepheids were made in the fifties almost simultaneously (Bahner et al. 1962, Walraven et al. 1958, Weaver et al. 1960). Even more cepheids were observed by Mitchell et al. (1964). Since then no extensive northern cepheid photometry has been carried out. The cepheid programme of Wisniewski and Johnson (1968) and that of Takase (1969) contained a small number of northern cepheids. It was therefore desirable to collect a new set of observations on a comparatively large number of northern cepheids. The main purposes of the present programme are as follows: 1/ To search for double mode cepheids in the northern sky: 2/ To investigate period changes; 3/ To examine secular variations of the light curves provided that they can be determined; 4/ To obtain photoelectric light curves from those cepheids which have not previously been observed photoelectrically. During the course of the first part of this work, 40 cepheids and 3 stars which proved to be misclassified variables were observed. 19 stars were observed in 3 colours of Johnson UBV system, the other 24 stars in B and in V light only. THE OBSERVATIONS The programme stars were selected from the General Catalogue of Variable Stars (Kukarkin et al. 1969-1970), its 1st and 2nd Supplements (Kukarkin et al. 1971, 1974) and from the current astronomical literature (newly discovered cepheids), with the restrictions that their declination should be north of 0— and B magnitude (or mpg for lack of photoelectric observations) at light minimum brighter than 12mag. The first part of the programme contains cepheids of both populations with a period of less than 5 days. Only \alpha UMi (Polaris) was omitted because of its brightness (there being no suitable nearby comparison star) and very small amplitude. These two factors did not allow a reliable light curve to be obtained. The stars investigated are listed in Table 1. The number of observations on each star, the colours, serial numbers of the pages where the individual observations and the O-C diagram with additional remarks on the given star can be found, are indicated Table 1 The programme Page Page Star N Col. obs. rem. Remarks Star N Col. obs. rem. Remarks DQ And 20 BV 11 57 V 1334 Cyg 22 UBV 22 63 FF Aql 21 UBV 11 92 BC Dra 102 BV - 6 RR Lyrae type star V 572 Aql 11 BV 12 68 the light curve AD Gem 17 BV 22 70 is not complete Y Aur 20 BV 12 77 BB Gem 22 BV 23 43 RT Aur 20 UBV 13 65 DX Gem 19 BV 23 53 SU Cas 28 UBV 13 38 BL Her 23 BV 23 33 SY Cas 27 BV 14 82 V Lac 22 UBV 24 102 TU Cas 311 UBV - 6 double mode cepheid Y Lac 21 UBV 25 86 XY Cas 17 BV 14 95 BE Mon 17 BV 25 50 BD Cas 22 BV 15 64 V 465 Mon 21 BV 25 51 BY Cas 24 BV 15 59 V 508 Mon 17 BV 26 84 DF Cas 24 BV 16 72 AU Peg 45 UBV 26 44 V 395 Cas 15 BV 17 81 SX Per 21 BV 27 85 V 445 Cas 50 BV - 6 eclipsing binary AS Per 29 BV 28 100 IR Cep 52 UBV 17 42 V 361 Per 56 UBV - 6 irregular variable BD+56—2806 32 BV 18 52 BQ Ser 122 BV - 6 double mode cepheid SU Cyg 21 UBV 19 73 ST Tau 20 UBV 28 80 VZ Cyg 25 UBV 19 96 SW Tau 40 UBV 29 36 DT Cyg 27 UBV 20 47 SZ Tau 20 UBV 29 55 V 402 Cyg 16 BV 20 88 EU Tau 28 UBV 30 41 V 532 Cyg 36 BV 21 62 T Vul 19 UBV 31 89 V 1154 Cyg 26 UBV 21 99 in the successive columns. The total number of observations is more than 1500. Most of the observations were made in the years 1972-1974, but some cepheids with changing period were reobserved in 1976-1977. Three variables proved to be misclassified. The star V445 Cas is an eclipsing binary of \beta Lyrae type with a period of 0.67352^d (Szabados 1974a); V361 Per is an irregular variable in the cluster h and \chi Per (Szabados 1974b); the third misclassified variable is BC Dra. This list star was announced as being a double mode cepheid (Szabados 1976a), but a recent more precise period analysis has shown that it is, in fact, an RR Lyrae type variable with a period of 0.71957^d (Szabados, Stobie and Pickup 1976). The observational data on these misclassified variables as well as on the double mode cepheids are not given here. There are two double mode cepheids in the northern sky, namely TU Cas and BQ Ser. The stars SW Tau and V 439 Oph classified as double mode cepheids (Latyshev 1963 and Gusev 1967, respectively) are simple cepheids of Population II with a long flat light maximum. The present set of observations has clearly shown that there are not more double mode cepheids among the known northern cepheid variables brighter than B = 12.5^m in minimum light. The observations and a detailed analysis of the data on TU Cas and BQ Ser will be published elsewhere. Short communications have been published on the recent photometry of these stars (Illes and Szabados 1976, Szabados 1976a). All the observations were made with two telescopes of the Konkoly Observatory: 1/ The 24 in. reflector (Budapest, Szabadsaghegy) combined with an unrefrigerated EMI 9502B photomultiplier; 2/ The 20 in. Cassegrain reflector (Piszkesteto Mountain Station) combined with an integrating photometer equipped with an unrefrigerated EMI 9058QB photomultiplier. The standard UBV photometric system was realized with the aid of the following Schott filters: 20 in. telescope 24 in. telescope U UG 2 2mm UG 1 2mm B BG12 1mm + GG13 2mm BG12 1mm + GG13 2mm V GG11 2mm GG11 2mm Because of the changeable sky conditions differential photometry was performed with a nearby comparison star being selected for each programme star. As a means of verifying the constancy of the comparison stars, check stars were regularly observed. The V magnitudes and the colour indices of the comparison and check stars are listed in Table 2. The data concerning the double mode cepheids and misclassified variables are omitted. The tie-in observations were made with the aid of UBV standard stars taken from the catalogue of Blanco et al. (1968). An asterisk instead of the name of the star in Table 2 denotes that the star is not in the Bonner Durchmusterung in which case the identification charts in Fig. 1a-f should be consulted. In these charts the letter a denotes the comparison star and the star marked b is the check one. (The size of the charts is about 25"x 25" , north is at the top.) Each observation of a cepheid is a result of at least 15 individual measurements or 80 sec of integration in each colour. One complete measurement of the variable, background and comparison star took on average of about twenty minutes. The mean error of an observation is about 0.010^m in V and B and 0.020^m in U. When the distance between the comparison star and the variable was greater than 1—, the effect of the atmospheric extinction was removed. The observational data have been transformed from the instrumental to the international UBV system using average values of transformation coefficients determined for both telescopes. After having transformed the data no systematic differences were found between the observations made with the 20" and those with the 24" telescope. The observations made with the 20" telescope are marked with asterisks in Table 3. The comparison between my photometric system (UBV_{sz}) and Schaltenbrand and Tammann's (1971) standard one (UBV_{scht}) gives the following transformation formulas: V_{sz} = V_{scht} (on the basis of 25 common stars) (B-V)_{sz} = 1.034(B-V)_{scht} - 0.066 (25 common stars) (U-B)_{sz} = 0.90 (U-B)_{scht} + 0.04 (13 common stars) The present V magnitudes and B-V colour indices are in good agreement with the standard values, while the deviation of (U-B)_{sz} from the standard U-B colour index may be explained by the fact Table 2 Variable Comp. V B-V U-B Check V B-V U-B Remark DQ And 10.86m 1.04m +44— 212 10m57 0.54m FF Aql +17— 3779 5.69 1.09 1.06m +17— 3778 6.69 -0.05 -0.32m V 572 Aql + 0— 4391 10.50 1.27 + 0— 4397 10.46 0.82 Y Aur +42— 1288 9.48 0.38 +42— 1297 10.16 0.25 1 RT Aur +29— 1154 4.33 1.02 0.80 +29— 1190 6.45 0.05 -0.05 SU Cas +67— 215 6.64 0.47 0.25 +67— 224 5.95 0.21 0.17 SY Cas +57— 41 9.44 1.12 +57— 38 9.28 1.70 XY Cas +59— 119 8.74 0.50 +59— 132 8.70 0.40 BD Cas 11.88 1.55 11.38 1.65 1 BY Cas +60— 345 9.77 0.58 +60— 346 9.90 1.24 DF Cas +60— 558 10.19 0.52 11.20 0.47 1 V 395 Cas +62— 356 10.01 1.15 +62— 359 9.18 1.86 IR Cep +60— 2324 8.90 0.15 0.12 +60— 2320 7.93 -0.03 -0.27 BD+56—2806 +56— 2815 8.67 0.15 +56— 2808 9.38 0.11 SU Cyg +28— 3447 6.54 0.35 0.28 +29— 3724 8.08 0.20 0.28 VZ Cyg +42— 4226 7.68 0.94 0.65 +42— 4225 9.39 1.14 0.95 DT Cyg +29— 4324 5.63 -0.08 -0.31 +30— 4322 7.56 -0.14 -0.59 2 V 402 Cyg +36— 3898 9.92 1.20 +36— 3904 9.51 0.46 V 532 Cyg +45— 3498 9.59 1.10 +45— 3496 9.85 0.50 V 1154 Cyg +42— 3473 9.25 1.23 0.99 +42— 3472 8.37 0.38 V 1334 Cyg +36— 4470 6.07 0.29 0.21 +36— 4557 5.92 -0.02 -0.84 Table 2 (cont.) Variable Comp. V B-V U-B Check V B-V U-B Remark AD Gem +21— 1358 8.96m 1.10m +21— 1355 9.35m 1.86m BB Gem +13— 1315 10.49 1.28 +13— 1309 9.72 0.23 DX Gem 10.44 0.45 * 10.92 1.50 BL Her +19— 3491 10.27 0.41 * 11.65 0.61 3 V Lac +55— 2824 9.57 0.49 0.12m +55— 2819 9.33 1.14 0.50m Y Lac +50— 3582 8.71 0.12 0.13 +50— 3596 8.26 0.01 -0.25 BE Mon + 7— 1388 9.75 0.41 + 7— 1390 10.63 0.13 V 465 Mon + 0— 1811 10.53 0.09 + 0— 1809 9.40 0.84 V 508 Mon + 4— 1437 10.25 0.01 + 3— 1398 8.56 0.49 AU Peg +17— 4575 9.29 0.97 0.70 +18— 4788 8.79 0.29 -0.03 SX Per +41— 841 10.73 0.73 * 11.09 0.54 AS Per +48— 1075 9.45 1.37 +48— 1074 10.51 1.12 ST Tau +13— 974 8.78 0.19 -0.21 +12— 889 7.44 0.80 0.45 SW Tau + 3— 596 8.11 0.98 0.56 + 4— 683 8.81 0.50 -0.09 SZ Tau +19— 744 6.34 0.74 0.33 +19— 731 7.11 0.46 0.08 EU Tau +18— 966 7.79 1.10 1.04 +18— 959 7.53 0.14 0.17 T Vul +26— 4017 4.57 0.84 0.46 - Remarks: 1 The comparison star has a faint companion within the edge of the diaphragm. 2 The comparison star is identical with V 389 Cyg, but the star seems to be non variable (see page 47). 3 The comparison star slightly varies. Figure 1a-f Identification charts Table 3 The observations DQ Andromedae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1567.523* 11.85 0.80 1918.531 * 11.46 0.58 1596.415* 11.87 0.80 1921.368 * 11.27 0.49 1597.450* 11.98 0.84 1921.518 * 11.34 0.55 1625.339* 11.91 0.86 1944.375 * 11.60 0.67 1650.248* 11.66 0.74 2008.560 * 11.63 0.72 1651.244* 11.97 0.85 2095.225 * 11.74 0.73 1651.382 * 11.99 0.84 2273.336 * 11.28 0.52 1688.242 * 11.56 0.61 2276.342 * 11.54 0.52: 1898.518 * 11.81 0.77 2276.474 * 11.32 0.54 1918.347 * 11.38 0.54 2426.210 * 12.03 0.81 FF Aquilae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1392.586 5.28 0.73 0.45 1459.544 5.34 0.68 0.48 1396.589 5.45 0.74 0.47 1466.435 5.47 0.83 0.50 1399.558 5.53 0.82 1467.498 5.53 0.77 0.53 1400.621 5.51 0.76 0.52 1472.478 5.46 0.77 1401.577 5.31 0.70 0.43 1487.468 5.29 0.69 0.46 1412.510 5.49 0.81 0.49 1489.534 5.55 0.79 0.56 1415.507 5.21 0.69 0.43 1501.409 5.38 0.75 0.52 1436.440 5.52 0.80 0.52 1529.389 5.56 0.78 1437.471 5.24 0.70 0.45 1554.312 5.25 0.66 0.46 1438.437 5.33 0.77 1758.629 5.44 0.76 0.52 1439.546 5.47 0.81 0.53 Observations in 1953 J.D.hel. \deltav \Deltab J.D.hel. \Deltav \Deltab 2430000+ 2430000+ 4583.367 -0.520 -1.042 4588.408 -0.641 -1.086 4585.392 -0.378 -0.685 4590.451 -0.266 -0.562 Table 3 (cont.) (FF Aql) J.D.hel. \DeltaV \Deltab J.D.hel. \DeltaV \Deltab 2430000+ 2430000+ 4591.404 -0.257 -0.620 4623.440 -0.348 -0.794 4596.368 -0.334 -0.772 4624.451 -0.562 -0.945 4597.406 -0.547 -1.030 4625.401 -0.328 -0.658 4598.406 -0.365 -0.755 4626.384 -0.201 -0.533 4600.397 -0.219 -0.529 4628.425 -0.425 -1.021 4602.458 -0.415 -0.822 4629.354 -0.435 -0.847 4608.381 -0.218 -0.498 4630.357 -0.280 -0.583 4609.520 -0.270 -0.605 4654.314 -0.285 -0.626 4614.435 -0.409 -0.759 4656.328 -0.381 -0.755 4619.366 -0.542 -0.975 4660.319 -0.493 -0.929 4621.427 -0.265 -0.547 4663.303 -0.286 -0.618 4622.410 -0.221 -0.452 4664.310 -0.578 -1.015 V 572 Aquilae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1567.365 11.05 0.86 1918.325 11.01 0.88 1568.291 11.08 0.85 1921.335 11.15 0.89 1896.479 11.20 0.98 1944.280 11.04 0.86 1897.371 11.40 1.08 2194.520 11.29 1.02 1898.422 11.23 0.97 2224.508 11.28 1.00 1917.365 11.23 0.92 Y Aurigae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1292.471 9.75 1.07 1401.352 9.99 1.04 1332.565 9.93 1.01 1402.362 9.67 0.87 1336.587 9.85 0.94 1679.540 9.97 1.06 1352.547 9.17 0.70 1682.524 9.82 1.04 1389.423 9.89 1.04 1694.462 9.93 1.04 1394.365 9.89 1.07 1696.485 9.28 0.79 Table 3 (cont.) (Y Aur) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1939.471 9.23 0.71 1990.399 9.52 0.92 1961.494 9.94 1.09 1990.577 9.60 0.97 1981.458 9.39 0.74 2039.378 9.29 0.73 1982.492 9.43 0.90 2141.295 9.63 0.95 RT Aurigae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1292.586 5.54 0.71 1697.402 5.12 0.45 0.28 1331.520 5.74 0.73 0.41 1758.360 5.44 0.67 0.39 1332.539 5.10 0.49 0.29 1990.478 5.76 0.76 0.47 1336.610 5.20 0.59 1990.660 5.77 0.77 0.55 1352.519 5.63 0.75 0.43 2018.648 5.15 0.52 0.28 1610.636 5.77 0.79 0.53 2066.404 5.20 0.55 0.32 1682.551 5.07 0.43 0.26 2100.296 5.01 0.43 0.28 1695.468 5.61 0.73 0.48 2108.301 5.27 0.54 0.35 1696.507 5.82 0.77 0.49 2148.281 5.47 0.59 0.19: 1697.358 5.20 0.45 0.26 2159.303 5.65 0.67 0.38 SU Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1301.349 5.93 0.75 1401.381 6.12 0.86 0.54 1352.578 6.15 0.80 1402.379 5.79 0.67 0.50 1389.450 6.09 0.83 0.49 1403.366 6.13 0.84 0.52 1390.447 5.80 0.68 0.44 1408.387 5.85 0.72 1391.386 6.10 0.81 0.54 1415.371 6.07 0.81 0.50 1392.404 5.76 0.71 0.45 1608.475 5.99 0.76 0.48 1393.385 6.11 0.83 0.49 1617.369 6.05 0.82 0.50 1394.388 5.77 0.69 0.45 1672.267 6.14 0.83 0.45 1396.420 5.76 0.65 0.49 1673.283 5.77 0.68 0.48 1399.363 6.11 0.82 1682.567 5.93 0.77 0.43 Table 3 (cont.) (SU Cas) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1694.441 5.82 0.71 0.49 1758.379 6.11 0.81 0.46 1695.441 6.09 0.82 0.50 1988.658 5.94 0.72 0.44 1753.396 5.81 0.73 0.44 1989.389 5.91 0.74 0.46 1754.334 6.12 0.84 0.58 1989.534 5.98 0.77 0.50 SY Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1302.383 10.16 1.12 1934.490 9.51 0.75 1586.499 10.05 1.11 1942.372 9.76 0.92 1589.518 9.76 1.01 1954.360 10.02 1.06 1594.472 9.96 1.06 1959.451 9.53 0.83 1596.463 9.58 0.85 1960.414 9.90 1.01 1597.462 9.66 0.92 1961.365 10.12 1.12 1606.455 9.91 1.09: 2008.506 9.61 0.90 1631.395 10.06 1.06: 2070.213 9.82 0.99 1634.345 9.75 0.95 2990.528 9.89 1.08: 1681.254 10.18 1.08 3045.535 9.96 0.94 1682.250 9.42 0.79 3048.541 10.16 1.06: 1689.227 10.17 1.16: 3050.525 9.59 0.84 1917.528 10.16 1.08 3078.380 9.55 0.80 1918.499 9.44 0.80 XY Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1589.548 10.00 1.21 1651.351 9.66 1.01 1596.448 10.05 1.11 1688.223 9.86 1.14 1597.473 9.67 1.01 1689.242 10.04 1.25 1625.386 9.91 1.14 1898.530 9.69 1.01 1647.344 9.77 1.07 1918.519 10.03 1.18 1650.363 10.11 1.19 1948.292 9.62 0.98 Table (cont.) (XY Cas) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 2095.247 10.16 1.23 2276.492 9.83 1.05 2275.542 10.17 1.21 2424.343 10.19 1.20 2276.351 9.92 1.07 Observations in 1967-1968 J.D.hel. \DeltaV \Deltab J.D.hel. \DeltaV \Deltab 2430000+ 2430000+ 9777.620 1.181 0.730 9806.350 0.864 0.351 9787.385 0.648 0.050 9807.660 1.068 0.576 9791.406 1.020 0.497 9808.502 1.255 0.859 9795.344 1.246 0.890 9810.287 0.666 0.023 9796.489 0.639 0.007 9821.351 1.174 0.829 9799.305 1.199 0.875 9864.284 0.689 0.052 BD Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1566.517 10.88 1.52 1651.296 10.95 1.46 1567.445 10.96 1.54 1651.370 10.95 1.53 1568.410 11.15 1.61 1688.206 11.05 1.57 1596.323 10.87 1.48 1689.203 11.17 1.62 1596.400 10.91 1.48 1896.490 11.04 1.63 1596.510 10.93 1.52 1897.463 11.12 1.55: 1597.420 11.10 1.63 1898.374 10.95 1.61 1597.513 11.11 1.64 1949.304 10.99 1.58 1625.369 10.85 1.50 2008.462 10.84 1.50 1629.262 10.89 1.51 2299.441 11.05 1.62 1650.372 10.89 1.57 2299.595 11.04 1.57 BY Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+. 2440000+ 1586.530 10.31 1.23 1594.492 10.42 1.19 Table 3 (cont.) (BY Cas) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1596.524 10.25 1.16 1682.267 10.46: 1.36: 1606.472 10.23: 1.14: 1933.445 10.56 1.30 1625.353 10.31 1.18 1935.378 10.14 1.15 1631.411 10.41 1.31 1935.535 10.16 1.19 1634.383 10.56 1.31 1949.413 10.47 1.28 1647.391 10.51 1.26 1961.511 10.23 1.18 1650.273 10.55 1.29 3045.560 10.59 1.28 1651.400 10.24 1.17 3048.552 10.53 1.26 1662.283 10.41 1.28 3050.537 10.18 1.13 1680.271 10.32: 1.11: 3078.316 10.56 1.30 1681.267 10.28 1.23 3140.259 10.34 1.19 Observations in 1967 J.D.hel. \DeltaV \Deltab J.D.hel. \Deltav \Deltab 2430000+ 2430000+ 9763.519 -0.196 -0.216 9791.423 -0.265 -0.302 9769.494 -0.385 -0.437 9795.531 -0.289 +0.020 9770.458 -0.067 +0.008 9796.469 -0.002 -0.325 9776.494 -0.175 +0.151 9799.324 -0.113 +0.072 9777.528 +0.017 -0.144 9810.303 -0.106 -0.137 9787.363 +0.021 +0.120 DF Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1330.355 10.97 1.25 1679.271 11.02 1.21 1594.518 10:90 1.15 1680.294 11.09 1.28 1596.546 10.85 1.15 1681.300 10.55 0.95 1634.430 11.14 1.19 1682.298 10.79 1.12 1650.308 10.71 1.07 1689.323 10.56 1.04 1650.453 10.60 0.99 1917.555 11.04 1.25 1651.323 10.66 1.09 1921.536 11.10 1.23 1651.427 10.68 1.10 1960.430 11.04 1.21 1662.323 10.53 1.00 1978.454 11.07 1.11 Table 3 (cont.) (DF Cas) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1981.403 10.81 1.19 3140.278 11.14 1.27: 2101.330 11.08 1.11: 3162.384 11.07 1.12 3078.332 11.02 1.24 3202.315 10.89 1.08: V 395 Cassiopeiae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1596.483 10.92 1.26 1917.541 10.46 1.07 1597.500 10.83 1.22 1918.567 10.74 1.22 1625.463 10.92 1.27 1921.377 10.40 1.05 1650.266 10.64 1.14 2008.572 10.95 1.26 1650.423 10.52 1.05 2276.502 10.39 1.00: 1651.309 10.55 1.10 2299.490 10.95 1.24 1651.411 10.57 1.11 2302.423 10.75 1.21 1688.293 10.71 1.20 IR Cephei J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1407.620 7.85 0.75 1881.423 7.85 0.88 0.53 1415.557 7.62 0.71 0.43 1882.538 7.59 0.73 0.44 1436.527 7.61 0.68 0.42 1897.475 7.61 0.68 0.40 1495.507 7.68 0.75 0.39 1898.542 7.91 0.86 1554.447 7.92 0.80 0.44 1904.505 7.82 0.84 0.52 1579.341 7.91 0.90 0.52 1905.583 7.77 0.76 0.46 1584.343 7.68 0.73 0.45 1906.440 7.71 0.81 0.48 1586.390 7.71 0.73 0.43 1907.415 7.90 0.86 0.55 1617.300 7.94 0.89 0.55 1907.529 7.88 0.81 0.64 1629.277 7.68 0.76 0.43 1908.531 7.77 0.76 0.51 1651.252 7.99 0.87 1911.393 7.99 0.88 0.56 1803.520 7.96 0.89 1911.579 7.93 0.88 0.55 1807.563 7.90 0.89 0.61 1917.386 7.89 0.84 Table 3 (cont.) (IR Cep) J.D.hel. V B-V U-B J.D.hel. B-V U-B 2440000+ 2440000+ 1917.489 7.92 0.86 0.47 1944.299 7.70 0.76 0.42 1917.588 7.96 0.85 1960.280 7.91 0.83 0.56 1918.309 7.75 0.76 0.38 1960.446 7.85 0.81 0.48 1918.541 7.61 0.67 0.40 1961.289 7.68 0.78 0.48 1921.354 7.79 0.80 0.44 1965.292 7.61 0.75 1921.472 7.85 0.83 1965.494 7.73 0.75 0.46 1921.569 7.89 0.83 1981.248 7.95 0.87 0.55 1932.510 7.97 0.87 0.60 1983.349 7.93 0.92 0.56 1933.333 7.59 0.67 0.44 2939.440 7.74 0.71 0.54 1933.422 7.59 0.68 0.50 3045.500 7.59 0.72 0.44 1934.373 7.90 0.85 0.64 3050.482 7.87 0.85 0.56 1934.470 7.93 0.87 0.53 3064.338 7.61 0.69 0.47 1935.497 7.55 0.76 0.38 3078.299 7.96 0.85 0.48 BD +56—2806 (Cep) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 2634.479 9.28 0.79 2720.376 9.53 0.89 2635.405 9.52 0.85 2728.315 9.54 0.97 2636.519 9.41 0.81 2738.372 9.28 0.80 2639.355 9.38 0.86 2743.344 9.33 0.88 2640.358 9.30 0.83 2756.239 9.53 0.97 2642.393 9.30 0.84 2767.190 9.50 0.85 2645.477 9.26 0.79 2770.195 9.51 0.94 2646.379 9.48 0.80 2776.185 9.56 0.98 2669.406 9.55 0.94 2776.305 9.55 0.96 2675.413 9.49 0.94: 2777.271 9.27 0.83 2676.397 9.25 0.83 2782.204 9.55: 0.84: 2685.490 9.40 0.82 2787.202 9.56 0.87 2712.420 9.37 0.87 2939.453 9.47 0.91 2714.378 9.58 0.92 2971.374 9.27 0.80 2715.330 9.34 0.84 2990.444 9.28 0.81 2715.433 9.31 0.81 3075.416 9.37 0.84 Table 3 (cont.) SU Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1412.596 7.16 0.68 0.43: 1880.362 6.90 0.63 0.46 1415.610 7.07 0.68 0.49 1881.375 7.16 0.68 0.40: 1436.484 6.67 0.43 0.42 1908.423 7.17 0.68 0.43 1476.478 6.86 0.65 0.47 1915.433 7.05 0.68 0.49 1495.446 6.81 0.60 1932.299 7.00 0.57 0.49 1554.349 7.09 0.66 0.44 1937.405 6.72 0.50 0.43 1561.482 6.98 0.66 0.46 1967.282 6.49 0.43 0.34 1584.309 6.96 0.62 0.51 1998.217 6.45 0.40 0.40 1606.325 6.53 0.46 0.41 1998.282 6.45 0.42 0.32 1610.294 6.59 0.46 0.42 2143.591 7.13 0.63 0.54 1789.582 7.16 0.69 0.54 Observations in 1953 J.D.hel. \DeltaV \Deltab J.D.hel. \DeltaV \Dletab 2430000+ 2430000+ 4584.492 0.097 0.383 4597.490 0.572 1.039 4585.496 0.428 0.906 4598.462 0.667 1.147 4590.530 0.614 1.184 VZ Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1472.515 8.62 0.80 1898.354 9.16 1.03 0.77 1589.443 8.66 0.79 0.63: 1900.446 8.62 0.72 0.44 1594.448 8.74 0.77 0.51 1904.490 9.01 0.84 0.55 1596.370 9.15 1.02 0.78 1914.398 8.86 0.76 0.42 1597.381 9.24 1.03 0.75 1914.566 8.71 0.72 0.42 1629.236 8.88 0.93 0.71 1929.338 8.64 0.70 0.42 1651.204 9.18 0.99 0.60 1942.430 9.22 1.08 0.59: 1860.466 9.16 0.97 0.58 2939.470 9.25 1.03 0.61: 1887.452 9.01 0.94 0.58 3045.466 9.05 1.00 1896.550 8.83 0.91 0.68 3048.490 8.59 0.73 0.42 1897.344 8.99 1.01 0.71 3064.324 8.91 0.90 0.68 Table 3 (cont.) (VZ Cyg) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 3075.394 9.12 1.06 3140.209 8.88 0.77 0.50 3078.280 8.75 0.86 0.45: DT Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1467.511 5.73 0.45 0.25 1877.536 5.67 0.46 0.25 1472.494 5.70 0.46 0.25 1881.445 5.91 0.56 0.28 1476.512 5.87 0.54 0.29 1882.522 5.67 0.44 0.24 1487.537 5.68 0.45 0.24 1884.541 5.85 0.50 0.25 1495.466 5.63 0.42 0.23 1908.349 5.75 0.51 0.23 1544.442 5.88 0.55 0.26 1908.472 5.81 0.51 0.27 1554.506 5.86 0.51 0.24 1911.560 5.91 0.54 0.28 1562.337 5.75 0.47 0.23 2307.473 5.66 0.41 0.21 1562.520 5.70 0.43 0.21 2990.473 5.81 0.48 0.28 1583.274 5.73 0.46 0.21 3045.313 5.73 0.45 0.32: 1606.304 5.83 0.54 0.28 3046.333 5.92 0.51 1613.247 5.71 0.47 0.20 3048.439 5.93 0.54 0.30 1634.272 5.94 0.56 0.25 3064.292 5.75 0.48 0.21 1860.531 5.67 0.45 0.23 V 402 Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1415.590 9.76 0.95 1629.195 9.62 0.96 1487.520 10.07 1.16 1803.506 9.56 0.93 1544.473 10.13 1.13 1874.437 9.82 1.06 1589.372 9.56 0.93 1900.369 9.78 1.03 1596.305 10.04 1.16 1901.521 10.00 1.18 1597.351 10.04 1.11 1902.439 10.17 1.16 1606.369 9.92 0.99 1949.282 9.97 1.15 1617.273 9.91 1.11 1981.231 10.20 1.05: Table 3 (cont.) V 532 Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1436.556 9.05 1.10 1904.520 9.07 1.13 1437.556 8.87 1.09 1906.409 9.07 1.00 1439.564 9.16 1.16 1907.550 9.00 1.06 1476.494 8.92 1.05 1915.555 9.22 1.16 1487.503 9.11 1.08 1917.470 9.00 1.12 1541.390 9.15 1.12 1921.453 9.18 1.18 1545.407 8.99 1.00 1930.389 8.92 1.08 1589.424 9.09 1.14 1933.371 8.90 1.04 1606.391 9.22 1.19 1934.441 9.12 1.22 1803.561 9.19 1.21 1944.451 9.19 1.19 1807.541 9.13 1.08 1961.270 9.21 1.21 1808.565 8.85 1.08 1978.422 9.12 1.10: 1869.479 9.19 1.18 2928.439 8.93 1.06 1874.417 8.89 1.08 2990.490 8.92 1.03 1897.328 8.89 1.07 3030.363 9.00 0.99 1898.388 9.16 1.19 3045.355 9.10 1.17 1901.544 9.16 1.16 3064.310 9.23 1.19 1903.509 8.91 1.00 3075.381 8.99 1.07 V 1154 Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1389.644 9.30 1.04 1412.488 9.20 1.02 0.89 1390.516 9.02 0.94 1415.459 8.95 0.89 0.52 1391.636 9.01 0.91 0.66 1436.403 9.03 0.95 1392.557 9.14 1.04 0.83 1436.578 9.13 0.97 0.71 1393.614 9.27 1.09 0.91 1437.439 9.12 1.06 1394.508 9.33 1.03 0.82 1437.587 9.19 1.09 1396.538 9.01 0.91 1438.391 9.35 1.07 1396.634 9.01 0.98 1439.396 9.17 0.99 1399.539 9.37 0.96: 1466.409 9.15 1.11 0.70 1400.609 8.97 0.87 1475.503 9.10 0.81: 0.70: Table 3 (cont.) (V 1154 Cyg) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1487.448 9.27 1.08 0.89 1765.601 8.88 0.86 1495.422 9.07 0.99 0.62 1808.549 9.25 0.97 0.70 1764.606 9.08 0.93 1900.426 9.15 1.12 0.79 V 1334 Cygni J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1554.404 5.78 0.52 0.19 1904.326 5.79 0.52 0.18 1561.501 5.80 0.54 0.19 1906.360 5.93 0.57 0.20 1562.377 5.93 0.56 0.19 1906.596 5.91 0.54 0.24 1579.296 5.96 0.56 0.17 1908.365 5.80 0.55 0.17 1606.347 5.94 0.57 0.18 1908.497 5.86 0.54 0.16 1607.354 5.80 0.53 0.20 1931.278 5.79 0.54 0.22 1853.517 5.89 0.52 0.21 1935.300 5.82 0.55 0.19 1877.397 5.78 0.54 0.17 1938.461 5.85 0.56 0.18 1881.389 5.80 0.53 0.19 1939.450 5.92 0.59 0.16 1900.331 5.83 0.57 0.14 1962.277 5.92 0.56 0.23 1903.332 5.90 0.55 0.19 1965.277 5.86 0.57 0.18 AD Geminorum J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1392.386 9.71 0.58 1954.643 10.11 0.81 1393.367 10.02 0.71: 1982.645 9.73 0.55 1394.334 10.20 0.77 1989.553 10.23 0.76 1679.496 9.87 0.58 1990.607 9.62 0.49 1680.490 9.78 0.63 2044.413 9.83 0.70 1681.481 10.03 0.77 2066.469 9.64 0.51 1682.489 10.16 0.80 2069.459 10.06 0.69 1764.338 9.94 0.76 2100.275 9.59 0.49 1766.319 10.20 0.72 Table 3 (cont.) BB Geminorum J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1608.599 11.56 0.89 1709.402 11.67 0.83 1610.614 11.73 0.79: 1954.631 11.74 0.80: 1634.552 11.00 0.64 1962.583 11.24 0.71 1662.469 11.26 0.67 1980.614 10.85 0.61: 1679.519 11.68 0.83 1982.629 11.34 0.62 1680.394 10.75 0.56 1987.643 10.97 0.63 1680.506 10.77 0.51 1988.592 11.57 0.80 1681.365 11.52 0.76 1989.618 10.93 0.61 1681.496 11.59 0.81 1990.524 11.37 0.81 1682.396 11.68 0.85 2066.286 11.20 0.60 1682.507 11.51 0.71 2069.298 11.52 0.85 DX Geminorum J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1634.534 10.55 0.86 2018.468 10.83 0.91 1662.490 10.65 0.91: 2018.624 10.86 0.94 1679.400 10.72 0.95: 2039.548 10.55 0.88 1680.412 10.90 0.98: 2101.302 10.85 0.83 1681.402 10.57 0.89 3124.520 10.63 0.86 1682.415 10.67 0.92 3138.489 10.80 0.90 1709.389 10.72 0.85 3162.433 10.56 0.82 1980.628 10.78 0.85: 3192.353 10.84 1.03 1981.638 10.86 0.94: 3210.281 10.60 0.87 1990.592 10.89 0.93 BL Herculis J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1366.648 9.79 0.25 1390.632 10.03 0.40 1390.618 10.03 0.40 1391.621 9.82 0.30 Table 3 (cont.) (BL Her) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1392.537 10.64 0.50 1932.328 10.48 0.51 1396.566 10.43 0.46 1933.294 10.18 0.44 1412.467 9.83: 0.19: 2132.616 10.50 0.51 1415.486 10.03 0.44 2152.602 9.89 0.49 1438.422 10.43 0.43 2159.524 10.27 0.49 1753.603 10.04 0.35 2161.495 10.28 0.36 1772.598 10.33 0.49 2255.366 10.51 0.56 1887.372 9.98 0.39 2277.357 10.25: 0.63: 1900.354 9.95 0.44 2314.302 10.57 0.56 1932.278 10.39 0.58 V Lacertae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1467.531 9.30 1.11 0.83: 1658.191 8.65 0.83 0.44 1475.517 8.89 0.91 0.41: 1900.561 9.16 1.13 0.71 1476.529 9.14 1.02: 1901.566 9.28 1.14 0.84: 1544.414 8.55 0.67 0.43: 1903.563 8.65 0.90 0.46 1545.517 8.88 1.02 0.58 1904.571 8.96 1.03 0.68 1589.465 8.62 0.82 0.45 1907.566 8.43 0.71 0.45 1594.433 8.61 0.82 0.55 2278.535 9.00 1.06 0.69 1597.407 9.32 1.13 0.57: 2297.493 8.77 0.93 0.48 1606.413 9.15 1.11 0.68 2316.475 8.42 0.72 0.41 1625.311 8.93 0.98 0.50 2350.274 9.30 1.07 0.63: 1634.236 8.60 0.80 0.46 2350.442 9.23 1.02 0.71 Observations in 1967 J.D.hel. \Deltav \Deltab \Deltau J.D.hel. \Deltav \Deltab \Deltau 2430000+ 2430000+ 9720.526 -0.582 -0.363 0.460 9739.533 -0.209 +0.128 0.911 9724.510 -0.106 +0.249 1.028 9753.379 +0.228 +0.770 1.771 9726.476 -0.249 +0.153 0.985 9763.576 +0.208 +0.738 1.785 9731.498 -0.217 +0.175 1.278 9795.263 -0.586 -0.261 0.445 9732.447 +0.029 +0.525 1.657 Table 3 (cont.) Y Lacertae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1466.514 8.97 0.67 0.60 1902.402 8.75 0.52 0.52 1589.490 9.45 0.74: 0.76: 1903.491 9.06 0.72 0.69 1594.410 9.42 0.80 0.67 1905.558 9.44 0.85 0.64 1596.388 9.05 0.69 0.47: 1906.456 8.85 0.56 0.49 1597.394 9.30 0.79 0.50: 1907.375 8.90 0.64 0.63 1604.414 8.82 0.60 0.48 1930.434 9.30 0.80 1606.435 9.33 0.86 0.69 1931.332 9.40 0.86 0.62 1629.285 9.32 0.76 0.44: 1932.473 8.82 0.56 0.47 1651.219 9.05 0.59 0.45 1980.390 8.78 0.54 0.54 1860.501 9.13 0.73 0.66 2027.224 9.15 0.73 0.49 1882.443 9.21 0.78 0.61 BE Monocerotis J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1329.470 10.67 1.24: 1982.599 10.66 1.08 1608.622 10.84 1.15 2018.550 10.36 1.00 1679.469 10.78 1.14 2044.369 10.79 1.19 1680.470 10.45 1.01 2069.483 10.34 0.97 1681.465 10.82 1.09 2070.358 10.53 1.04 1682.474 10.55 1.00 2101.404 10.77 1.09 1960.616 10.86 1.05: 2429.393 10.28 0.96 1961.598 10.32 0.95 2429.470 10.24 0.93 1981.625 10.71 1.24: V 465 Monocerotis J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1329.502 10.20 0.60 1679.441 10.23 0.59 1331.493 10.47 0.72 1680.451 10.42 0.69 1332.479 10.19 0.63 1681.445 10.54 0.70 Table 3 (cont.) (V 465 Mon) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1682.456 10.20 0.62 2044.520 10.50 0.80 1961.611 10.23 0.60 2066.447 10.54 0.79 1962.602 10.42 0.69 3124.537 10.58 0.68: 1982.553 10.57 0.73 3138.474 10.44 0.80 1988.575 10.30 0.59 3162.403 10.57 0.74 1989.566 10.36 0.68 3209.293 10.38 0.68 1990.558 10.54 0.83 3210.293 10.25 0.68 2044.391 10.56 0.77 V 508 Monocerotis J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1311.527 10.56 0.86 1982.567 10.74 0.94 1679.423 10.53 0.90 1989.633 10.56 0.89 1680.433 10.69 0.93 1990.643 10.65 1.01 1681.423 10.76 0.90 2066.341 10.55 0.84 1682.436 10.34 0.72 2066.514 10.44 0.81 1764.311 10.66 0.79: 2070.378 10.55 0.83 1765.308 10.32 0.78 2089.366 10.64 0.96 1980.598 10.40 0.81 2148.302 10.70 0.96 1981.570 10.55 0.95 AU Pegasi J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1495.491 9.30 0.75 1613.227 9.33 0.78 1561.409 9.23 0.64 1617.226 9.20 0.62 1562.360 9.20 0.74 0.43: 1623.253 9.47 0.84 0.51: 1589.399 9.40 0.83 0.39: 1629.213 9.14 0.73 0.44 1596.341 9.32 0.83 0.51: 1853.536 9.38 0.75 1597.364 9.23 0.69 0.41: 1860.484 9.32 0.82 1610.306 9.12 0.77 1869.501 9.15 0.74 0.42: Table 3 (cont.) (AU Peg) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1874.453 9.19 0.79 0.56: 1938.444 9.09 0.73 1875.518 9.42 0.78 0.48: 1942.407 9.46 0.79 1897.360 9.31 0.76 0.43 1944.436 9.33 0.82 0.51 1898.336 9.14 0.78 1960.300 9.09: 0.65: 1900.468 9.15 0.65 0.39: 1961.379 9.32 0.87 1904.451 9.38 0.81 0.35: 1978.247 9.36 0.80 1906.396 9.45 0.78 1982.311 9.16 0.72 1907.449 9.13 0.66 1983.304 9.35 0.88 1917.457 9.12 0.74 0.48 2939.489 9.38 0.77 1921.440 9.27 0.70 0.39 2990.461 9.14 0.64 1928.441 9.42 0.77 3030.386 9.51 0.82 1930.451 9.39 0.80 3045.344 9.34 0.67 1931.353 9.18 0.64 0.29: 3048.425 9.12 0.68 0.37 1932.315 9.24 0.75 3075.368 9.20 0.80 1933.355 9.39 0.71 3078.266 9.41 0.81 1934.412 9.15 0.80 SX Persei J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1304.349 11.02 1.19 1961.401 11.24 1.25 1596.581 11.18 1.35: 1980.457 11.19 1.20 1650.492 10.77 0.88 1980.586 11.05 1.10 1651.478 10.91 1.18: 1981.378 10.73 1.04 1679.294 11.38 1.35: 1982.384 11.03 1.27 1681.323 10.84 1.07 1988.607 11.45 1.32 1682.315 11.14 1.26 1989.586 10.69 0.91 1931.539 11.25 1.22 2039.336 11.39 1.27 1932.583 11.38 1.32 2069.222 11.38 1.22 1954.565 11.38 1.18 2101.351 10.68 1.07 1960.508 10.96 1.12 Table 3 (cont.) AS Persei J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1304.404 9.04 1.61 2001.459 9.92 1.56 1401.333 9.32 1.32 2066.272 9.85 1.50 1402.342 9.60 1.50 2066.488 9.62 1.38 1606.633 9.71 1.53 2070.399 10.02 1.57 1634.453 9.20 1.21 2141.277 9.35 1.32 1679.314 9.19 1.24 3078.406 9.75 1.47 1680.522 9.54 1.46 3124.504 9.93 1.60 1681.507 9.81 1.50: 3140.298 9.88 1.51 1694.476 9.28 1.27 3162.342 9.53 1.45 1772.308 10.01 1.57 3176.417 9.30 1.35 1931.596 10.00 1.55 3178.223 9.81 1.50 1935.460 9.80 1.55: 3191.239 9.22 1.37 1935.612 9.90 1.61 3209.253 9.98 1.59 1942.484 9.30 1.24 3210.313 9.51 1.28 1963.476 9.42 1.39 ST Tauri J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1302.503 7.89 0.78 1696.286 8.53 1.06 0.62 1352.433 8.39 0.99 0.69 1697.334 7.81 0.69 0.50 1366.311 8.04 0.77 0.48 1712.247 8.54 1.01 0.76: 1392.359 8.27 0.96 0.51: 1761.314 8.41 0.95 0.63 1608.578 7.81 0.71 0.45 1960.526 8.09 0.86 0.52 1610.554 8.37 1.01 0.58 1980.470 7.97 0.82 0.51 1673.347 7.81 0.68 0.49 1981.497 8.29 1.00 0.70: 1680.351 8.53 1.03 0.63 2018.424 8.45 1.04 0.66 1682.362 8.11 0.93 0.54 2018.581 8.50 1.02 0.61: 1695.416 8.41 1.03 0.66 2039.570 8.54 1.04 0.67: Table 3 (cont.) SW Tauri J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1303.532 9.87 0.70 1961.525 9.40 0.46 0.17 1352.378 9.81 0.52: 1961.570 9.41 0.44 0.20 1366.270 9.38 0.44 0.23 1961.631 9.40 0.45 0.19 1586.591 9.48 0.58 1981.476 10.02 0.72 0.60: 1589.589 9.34 0.49 1982.540 9.58 0.57 0.24: 1596.603 9.93 0.75: 0.46: 1982.617 9.70 0.64 1606.603 10.04 0.62 1984.534 9.94 0.69 1606.609 9.96 0.68 1989.650 10.11 0.74 1610.597 9.79 0.62 0.31 2018.446 9.52 0.47: 1617.437 10.08 0.80 2039.358 9.39 0.43 0.17 1680.318 9.82 0.63 2039.418 9.49 0.48 0.19 1681.343 9.41 0.44 2044.285 9.54 0.60 0.24 1682.348 10.10 0.77 2044.335 9.68 0.58 0.22 1689.346 9.37 0.45 0.39: 2044.439 9.77 0.62 0.45 1694.355 9.61 0.58 2066.381 9.46 0.50 1695.333 9.81 0.60 2070.257 10.09 0.74 0.27 1695.341 9.78 0.56 3124.487 9.75 0.75: 1929.592 10.17 0.70 0.30: 3162.323 9.60 0.56 0.36 1930.598 9.84 0.67 0.32: 3202.262 9.90 0.66 1954.617 10.05 0.75 0.41: 3209.265 9.56 0.58 0.09 SZ Tauri J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1303.555 6.39 0.74 1694.369 6.41 0.80 0.43 1352.405 6.71 0.91 0.42: 1695.389 6.66 0.95 0.54 1366.293 6.34 0.77 0.42 1696.263 6.56 0.82 0.45 1608.646 6.39 0.75 0.41 1754.303 6.44 0.81 0.34: 1610.576 6.69 0.91 0.48 1954.594 6.50 0.81 0.41 1673.308 6.68 0.92 0.55 1966.565 6.68 0.91 0.43: 1680.334 6.60 0.84 0.43 1981.657 6.64 0.88 0.50 1682.331 6.59 0.89 0.49 1982.473 6.65 0.88 0.58: Table 3 (cont.) (SZ Tau) J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1984.492 6.51 0.89 0.45 1990.626 6.51 0.83 0.40 1989.505 6.42 0.78 0.39 2018.509 6.39 0.77 0.41 0bservations in 1967 J.D.hel. \Delta \Deltab \Deltau J.D.hel. \Deltav \Deltab \Deltau 2430000+ 2430000+ 9770.518 0.049 0.104 0.165 9806.424 0..351 0.521 0.734 9776.536 0.029 0.061 0.130 9810.561 0.174 0.227 0.293 9777.504 0.252 0.379 0.522 9815.603 0.314 0.509 0.698 9782.598 0.060 0.116 0.199 9825.652 0.375 0.562 3787.546 0.349 0.544 0.666 9838.491 0.274 0.389 0.469 9791.476 0.250 0.318 0.368 9845.373 0.088 0.120 0.222 9796.575 0.296 0.426 0.686 EU Tauri J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1302.577 8.21 0.73 1962.546 8.29 0.74 0.58 1352.462 8.23 0.75 0.48 1966.584 8.27 0.76 0.53 1364.385 8.01 0.66 1980.658 8.08 0.68 0.54 1395.370 8.06 0.69 0.56 1981.553 8.29 0.72 0.56 1610.533 8.03 0.67 0.50 1982.660 8.04 0.67 0.53 1673.328 7.93 0.64 1984.568 8.02 0.62 1680.375 8.20 0.72 0.52 2018.527 8.10 0.69 0.52 1681.360 8.05 0.63 0.46: 2035.413 8.13 0.69 1682.377 8.19 0.71 0.54 2044.309 8.29 0.75 0.55 1694.425 7.98 0.62 0.47 2066.245 8.00 0.61 0.53: 1695.368 8.27 0.76 2066.427 7.96 0.62 0.48 1759.317 8.01 0.61 2069.316 8.23 0.73 0.54 1939.630 8.25 0.70 0.64: 2070.234 8.10 0.66 0.54 1961.552 8.02 0.65 0.50 2108.253 8.01 0.64 Table 3 (cont.) T Vulpeculae J.D.hel. V B-V U-B J.D.hel. V B-V U-B 2440000+ 2440000+ 1472.536 5.98 0.77 0.46 1617.239 5.61 0.59 0.27 1475.537 5.66 0.65 0.26: 1868.431 5.97 0.74 0.36 1476.547 5.92 0.75 0.49 1877.382 5.96 0.65 0.24: 1477.538 6.04 0.79 0.45 1880.378 5.97 0.74 0.47 1495.525 6.05 0.77 0.48 1900.544 5.46 0.50 0.24 1496.472 5.44 0.51 0.26 1904.430 5.59 0.49 0.23 1554.374 5.42 0.49 0.23 1905.324 5.54 0.56 0.30 1561.463 6.00 0.79 0.41 1906.377 5.82 0.71 0.42 1579.318 6.03 0.76 0.47 1935.279 5.71 0.60 0.28 1584.406 6.08 0.72 0.41 Observations in 1953 J.D.hel. \DeltaV \Deltab J.D.hel. \DeltaV \Deltab 2430000+ 2430000+ 4584.534 -0.470 +0.760 4597.559 -0.527 +0.550 4585.545 -0.684 +0.392 4608.546 -1.281 -0.492 4590.569 -1.187 -0.395 4609.540 -0.884 +0.010 that my observations were made at less than 1000 meters above sea level. Table 3 contains the observations in alphabetical order of the constellations. Some unpublished observations made by Prof. L. Detre in 1953 and by Dr. J. Abaffy in 1967-1968 are also listed in Table 3. Unfortunately, since the comparison stars used by them are unknown in several cases these two sets of observations have not been transformed to the standard system, and only the magnitude differences are given in the instrumental system. THE LIGHT CURVES AND PERIOD CHANGES OF THE INDIVIDUAL VARIABLES This section contains the light curves, the tables and the graphs of the O-C values and some remarks on the observed cepheids. The variables were arranged according to the length of their period. Such a sequence is obvious because both the form of the light curve and the rate of the period changes vary with the period itself. The light and colour curves are constructed from the observations listed in Table 3 using the actual periods available after constructing the O-C diagrams. The value of the actual period is indicated for each light curve. All the available observational material on each cepheid has been gathered so that the period changes can be studied. If the individual observations are available in published form, they were plotted with an approximately correct value of the period and the moment of the normal light maximum was determined. The moment of the median brightness on the ascending branch could also be determined in several cases. The median brightness is the brightness at half the amplitude. The moment of median brightness on the ascending branch can be determined more precisely than can the moment of the maximum because of steep rise in the brightness on the ascending branch. If, however, a light curve of good quality is available the moment of median brightness can be determined accurately. In the case of visual and photographic light curves with large scatter I determined the moments of maxima by fitting the new photoelectric light curve. For the earlier photoelectric observations the light curve in band B (or the band closest to B) was used for the determination of moments of maximum and median brightnesses. The difference between the moments of maxima in B and V lights can be ignored. Although there is a systematic difference in the sense that the longer the wavelength the later the moment of the maximum takes place, the scatter of the points on the O-C diagram is much larger than this difference. In the case of individual observations not having been published, the normal maximum taken from the original reference was used for constructing the O-C diagram. If more than one maximum in the same year is published, the yearly mean of the O-C values was determined from these maxima. The O-C values determined on the basis of visual, photographic and photoelectric observations are marked with open circles, filled circles and triangles, respectively. The size of these marks denotes the weight of the O-C values to be found in the figures of this section. The formulae by which the O-C residuals have been calculated are indicated at each variable. These formulae usually refer to maximum light. If O-C diagrams for both maximum and median brightnesses are presented the two different calculated ephemerides are marked with C_{max} and C_{med} respectively. O-C diagrams for the median brightness are published here only if they are fairly complete. BL Herculis This is a short period Population II cepheid. Its light curve is typical of the class to which this star belongs. Unfortunately, Figure 2 V and B-V curves of BL Her the comparison star BD +19—3491 seems to be slightly variable in V light therefore the V light curve shows larger scatter than might otherwise have been expected due to the observational errors (see Fig. 2). The B light curve shows no mark of variability of the comparison star. According to Madore (1977), BL Her has a blue photometric companion. The O-C residuals have been computed by the formulae: C_{max} = 2441841.289 + 1.3074502d*E ; Table 4 O-C residuals for BL Her Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2415196.499 -20379 -0.262d phg 0.5 Jacchia (1940) 2420005.423 -16701 -0.140 phg 1 Parenago (1939a) 2426222.400 -11946 -0.089 vis 1 Esch (1933) 2426503.16 -11731 -0.43 vis 0 Jacchia (1931) 2428384.974 -10292 -0.038 phg 2 Wachmann (1940) 2428734.030 -10025 -0.071 phg 1 Parenago (1939a) 2428955.025 2428954.874 -9856 -0.035 -0.070d phg 2 Wachmann (1940) 2429481.898 2429481.805 -9453 -0.064 -0.042 phg 2 Binnendijk (1950) 2430353.989 2430353.874 -8786 -0.043 -0.043 phg 2 Binnendijk (1950) 2431994.845 2431994.743 -7531 -0.037 -0.023 phg 2 Binnendijk (1950) 2433661.858 -6256 -0.023 phg 1 Solov'yov (1957) 2433661.872 -6256 -0.009 phg 1 Borzdyko (1965) 2433816.153 -6138 -0.007 phel 3 Eggen et al. (1957) 2433860.612 -6104 -0.001 vis 0.5 Koval' (1957) 2433861.986 -6103 +0.066 phg 0.5 Tschuprina (1954) 2433948.198 -6037 -0.014 phg 0.5 Vasil'yanovsk. et al.^1(1970) 2434200.543 -5844 -0.007 phg 0.5 Mandel' (1970) 2434200.547 -5844 -0.003 vis 0.5 Koval' (1957) 2434584.916 -5550 -0.024 phg 0.5 Mandel' (1970) 2434903.950 2434903.844 -5306 -0.008 +0.001 phel 3 Abt, Hardie (1959) 2435457.028 -4883 +0.018 phg 0.5 Vasil'yanovsk. et al^1.(1970) 2435488.388 -4859 0.000 phg 0.5 Mandel' (1970) 2435667.508 -4722 -0.001 phel 3 Abt, Hardie (1959) Table 4 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2435871.472 -4566 +0.001d phg 1 Borzdyko (1965) 2436023.157 -4450 +0.021 phg 0.5 Vasil'yanovsk. et al. (1970) 2436083.265 -4404 -0.013 phg 0.5 Mandel' (1970) 2436387.912 -4171 -0.002 phg 0.5 Mandel' (1970) 2436416.659 -4149 -0.019 phg 0.5 Mandel' (1970) 2436771.011 -3878 +0.014 phg 0.5 Mandel' (1970) 2436780.171 -3871 +0.022 phg 1 Borzdyko (1965) 2436832.457 -3831 +0.010 phg 0.5 Huth (1963c) 2437080.876 -3641 +0.013 phg 0.5 Mandel' 1970) 2437143.625 -3593 +0.005 phg 0.5 Mandel' (1970) 2437287.457 -3483 +0.017 phg 0.5 Vasil'yanovsk. et al.^1(1970) 2437454.801 -3355 +0.007 phel 2 Mitchell et al. (1964) 2437501.843 -3319 -0.019 phg 0.5 Mandel' (1970) 2437565.911 -3270 -0.016 phg 0.5 Borzdyko (1965) 2437871.855 2437871.746 -3036 -0.015 -0.009d phel 3 Michalowska-Smak, Smak (1965) 2437871.861 -3036 -0.009 phg 0.5 Mandel' (1970) 2438390.918 -2639 -0.010 phg 0.5 Mandel' (1970) 2438392.227 -2638 -0.008 phg 0.5 Mandel' (1970) 2438434.072 -2606 -0.002 phg 0.5 Vasil'yanovsk. et al.^1 (1970) 2438967.514 -2198 +0.001 phg 0.5 Mandel' (1970) 2439328.253 -1922 -0.002 phel 2 Preston, Kilston (1967) 2441841.293 2441841.180 0 +0.004 +0.006 phel 3 present paper Remark: 1 Observer: Shakhovskaya. C_{med} - 2441841.174 + 1.3074502d*E . The O-C diagram (Fig. 3) for the maximum light can be interpreted in two different ways. It may consist of two straight lines, or can be represented by a negative parabola. This uncertainty results from the smallness of the period variation. Assuming the Figure 3 O-C diagram of BL Her case of sudden period change the values of the period were 1.3074604d before J.D. 2435000 and 1.3074502d after J.D. 2435000. The approximation of the O-C diagram with a parabola is as follows: C^'_{max} = 2434999.402 + 1.307457d*E - 3.9d*10^{-10}*E^2. SW Tauri This star is a short period Population II cepheid. This classification is supported by the shape of the light curves and the phase shift between the minimum value of U-B colour index and the light maximum in V (see Fig. 4). According to Mandel's (1970) photographic observations there is a small bump on the light curve of SW Tau near its minimum brightness. Unfortunately, neither the photoelectric observations made by Milone (1970) nor the present observations provides enough data about the minimum, to prove the presence of this bump. Nevertheless, the photoelectric observations show a stable light curve though Latyshev (1963) listed SW Tau among double mode cepheids. SW Tau is a representative of short period flat-topped cepheids. The star reaches its light maximum after a very slow increase of brightness. The point of maximum is at the right end of the flat top. Earlier the maximum was thought to be at the mid-phase of the top, therefore a small correction has been applied in determining O-C residuals should the original observations not be pub- Figure 4 V, B-V and U-B curves of SW Tau Figure 5 O-C diagram of SW Tau Table 5 O-C residuals for SW Tau Obs.Max.J.D. E O-C Type w Source 2418240.787 -14806 -0.38d vis 0.5 Munch (1909) 2419730.929 -13865 -0.449 phg 0.5 Robinson (1930) 2420440.44 -13417 -0.38 vis 0.5 Hoffmeister (1919) 2420842.84 -13163 -0.21 vis 0 Hoffmeister (1919) 2421200.62 -12937 -0.32 vis 0.5 Hoffmeister (1919) 2430434.692 -7106 -0.130 phg 1 Solov'yov (1957) 2432354.063 -5894 -0.063 phg 1 Borzdyko (1965) 2433473.67 -5187 -0.05 phg 0.5 Vasil'yan, et al. (1970) 2433638.348 -5083 -0.065 phel 2 Eggen et al. (1957) 2434377.922 -4616 -0.024 phg 1 Borzdyko (1965) Table 5 (cont.) Obs.Max.J.D. E O-C Type w Source 2435000.23 -4223 -0.06d phg 0.5 Vasil'yan. et al. (1970) 2435502.195 -3906 -0.096 phg 0.5 Stilijanow (1966) 2435774.64 -3734 -0.03 phg 0.5 Vasil'yan. et al. (1970) 2435879.196 -3668 +0.012 phg 1 Borzdyko (1965) 2436197.508 -3467 +0.024 phg 0.5 Stilijanow (1966) 2436555.339 -3241 -0.035 phg 0.5 Mandel' (1970) 2436846.699 -3057 -0.055 phg 0.5 Stilijanow (1966) 2437003.558 -2958 +0.029 phg 0.5 Borzdyko (1965) 2437147.64 -2867 +0.01 phg 0.5 Vasil'yan. et al. (1970) 2437465.884 -2666 -0.051 phg 1 Mandel' (1970) 2437584.694 -2591 -0.010 phg 0.5 Stilijanow (1966) 2437907.713 -2387 -0.042 phg 0.5 Stilijanow (1966) 2438083.498 -2276 -0.035 phg 0.5 Stilijanow (1966) 2438376.52 -2091 +0.02 phg 0.5 Vasil'yan. et al. (1970) 2438441.416 -2050 -0.007 phg 0.5 Stilijanow (1966) 2438894.340 -1764 +0.012 phg 0.5 Mandel' (1970) 2439059.029 -1660 +0.008 phel 3 Milone (1970) 2439063.790 -1657 +0.019 phg 0.5 Stilijanow (1966) 2439078.025 -1648 +0.001 phel 3 Wamsteker (1972) 2441687.773 0 +0.003 phel 3 present paper 2443176.335 +940 -0.004 phel 2 present paper lished. The true maximum in B is 0.1d later than the mid-phase of the top. The O-C residuals have been computed with the formula: C = 2441687.770 + 1.583584d*E . Figure 5 shows a period change at J.D. 2436000. Before this change the value of the period was 1.583623, after J.D. 2436000 the period is 1.583584. SU Cassiopeiae Figure 6 V, B-V and U-B curves of SU Cas Table 6 O-C residuals for SU Cas Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2417287.164 2417286.809 -12496 -0.28d +0.005d vis 1 Muller, Kempf (1907) 2417347.775 -12465 +0.164 vis 0 Munch (1910) 2417482.181 -12396 +0.067 vis 0.5 Muller, Kempf^1 (1907) 2417770.629 2417770.223 -12248 +0.015 -0.013 phg 2 Parkhurst (1908) 2417794.090 -12236 +0.084 vis 0.5 Zeipel (1908) 2418055.209 -12102 -0.006 vis 0.5 Nijland (1923) 2418873.924 -11682 -0.006 vis 0.5 Nijland (1923) 2420025.890 -11091 -0.090 vis 0.5 Hoffmeister (1915) 2421394.42 -10389 +0.02 vis 1 Vogelenzang (1922) 2422285.552 -9932 +0.308 vis 0 Ellsworth (1928) 2423115.771 -9506 +0.116 vis 0 Ellsworth (1928) 2423386.570 -9367 -0.041 vis 0.5 Hellerich (1926a) 2423677.080 -9218 +0.020 vis 0.5 Hopmann (1926a) 2424148.790 2424148.410 -8976 -0.006 -0.008 vis 1 Parenago (1938) 2424840.855 2424840.524 -8621 +0.050 +0.097 vis 0.5 Kukarkin (1940) 2425051.298 2425050.955 -8513 -0.034 +0.001 phg 1 Hellerich (1935) 2425096.155 2425095.820 -8490 -0.011 +0.032 vis 1 Parenago (1938) 2425283.360 2425282.981 -8394 +0.059 +0.058 vis 1 Kukarkin (1940) 2425630.257 2425629.916 -8216 -0.023 +0.014 vis 1 Zverev (1936) 2425698.552 2425698.248 -8181 +0.043 +0.119 vis 0.5 Kukarkin (1940) 2425747.254 2425746.862 -8156 +0.014 0.000 vis 1 Parenago (1938) 2425969.403 -8042 -0.059 vis 0.5 Florya, Kukarkina (1953) 2426086.404 2426086.094 -7982 -0.018 +0.050 vis 1 Zverev (1936) 2426560.123 -7739 +0.016 vis 0.5 Kukarkin (1940) 2426755.064 2426754.688 -7639 +0.025 +0.027 phg 1 Kox (1935) 2426766.766 2426766.362 -7633 +0.031 +0.005 vis 1 Florya, Kukarkina (1953) 2426895.330 2426894.938 -7567 -0.060 -0.074 phg 1 Hasenstein (1954) 2427127.283 2427126.900 -7448 -0.077 -0.082 vis 1 Parenago (1938) 2427881.760 -7061 +0.013 vis 1 Krebs (1937a) 2428144.865 -6926 -0.041 vis 1 Krebs (1937a) Table 6 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2429181.912 -6394 -0.033d phg 1 Mandrykina (1949) 2430404.167 2430403.793 -5767 -0.003 +0.001 phel 3 Walter (1943) 2430905.119 2430904.784 -5510 -0.027 +0.016 phel 3 Groeneveld (1944) 2432639.97 -4620 -0.07 vis 0.5 Pohl^2 (1950) 2435755.041 2435754.663 -3022 -0.018 -0.018 phel 3 Prokof'yeva (1961) 2436199.516 -2794 +0.012 phel 2 Svolopoulos (1960) 2436836.942 -2467 +0.009 phel 2 Bahner et al. (1962) 2437439.297 2437438.927 -2158 +0.024 +0.032 phel 3 Mitchell et al. (1964) 2437987.089 -1877 +0.054 vis 0.5 Kunicki (1972) 2438384.671 2438384.291 -1673 -0.023 -0.025 phel 3 Wisniewski, Johnson (1968) 2439055.269 2439054.887 -1329 +0.008 +0.004 phel 3 Milone (1970) 2439361.299 2439360.919 -1172 -0.006 -0.008 phel 3 Takase (1969) 2439447.074 2439446.719 -1128 -0.001 +0.022 phel 3 Wamsteker (1972) 2439751.198 2439750.759 -972 +0.029 -0.032 phel 2 Sudzius (1969) 2439864.198 2439863.859 -914 -0.032 +0.007 phel 3 Reed (1968) 2441645.925 2441645.537 0 +0.015 +0.005 phel 3 present paper 2441930.480 +146 -0.021 phel 3 Gieren (1976) Remarks: 1. Observer: Graff 2. Observer: Pocher Figure 7 O-C diagram of SU Cas This is a cepheid with small amplitude (see Fig. 6). According to Kukarkin et al. (1971) its period probably varies. However, neither the O-C diagram of the maximum brightness, nor that of the median brightness shows any changes in the period. The O-C residuals plotted in Fig. 7 have been computed with the formulae: C_{max} = 2441645.910 + 1.949322d*E ; C_{med} = 2441645.532 + 1.949322d*E . The period of SU Cas has been constant since the discovery of its light variation. EU Tauri EU Tau is a cepheid with small amplitude (see Fig. 8). There are only four valuable sets of observations within a short time interval therefore the O-C residuals given in Table 7 are not plotted in a separate figure. The residuals have been derived using the formula: C = 2441704.785 + 2.10248d*E . Figure 8 V, B-V and U-B curves of EU Tau Table 7 O-C residuals for EU Tau Obs.Max.J.D. E O-C Type w Source 2438973.668 -1299 +0.005d phel 3 Guinan (1972) 2440998.346 -336 -0.006 phel 3 Wachmann (1976) 2441334.746 -176 -0.003 phel 3 Sanwal et al. (1974) 2441704.788 0 +0.003 phel 3 present paper IR Cephei The newly discovered cepheid variable IR Cep = HBV 476 belongs to the group of small amplitude cepheids (see Fig. 9). However, Figure 9 V, B-V and U-B curves of IR Cep the light curve is not symmetrical (or "sinusoidal"), i.e. it differs markedly from the other small amplitude cepheids in the shape of the light curve. There are two possible explanations for resolving this difference: 1/ the variable star has a companion that reduces the amplitude of the light variation; 2/ the group of cepheids with small amplitude is not homogeneous, it includes cepheids with nearly symmetrical as well as non-symmetrical light curves. In order to decide whether the first explanation is valid, spectroscopic observations are highly desirable. The O-C residuals have been computed with the formula: C = 2441696.582 + 2.114124d*E . These residuals are plotted in Fig. 10. The period of IR Cep Figure 10 O-C diagram of IR Cep Table 8 O-C residuals for IR Cep Obs.Max.J.D. E O-C Type w Source 2428335.914 -6320 +O.596d phg 1 Klawitter (1971) 2429515.512 -5762 +0.512 phg 1 Klawitter (1971) 2430373.783 -5356 +0.449 phg 1 Klawitter (1971) 2430517.605 -5288 +0.511 phg 1 Klawitter (1971) 2430703.620 -5200 +0.483 phg 1 Klawitter (1971) 2431033.395 -5044 +0.454 phg 1 Klawitter (1971) 2440965.096 -346 +0.001 phel 3 Wachmann (1976) 2441696.580 0 -0.002 phel 3 present paper 2443045.394 +638 +0.001 phel 2 present paper shows one strong change. Before J.D. 2440900 the period was 2.114027d or even smaller, after J.D. 2440900 the period is 2.114124d. BB Geminorum Figure 11 V and B-V curves of BB Gem The star BB Gem is a Population II cepheid. According to Efremov (1968b) the maximum value of the light amplitude of classical cepheids in the blue band is about 0.85m at log P = 0.36. BB Gem has an amplitude of 1.27m in band B (see Fig. 11). This extremely large amplitude supports the above-mentioned new classification for this cepheid. The O-C residuals for this star have been obtained by the formula: C = 2441839.695 + 2.308207d*E These residuals are plotted in Fig. 12. The period of BB Gem has remained constant for more than 7000 epochs. Figure 12 O-C diagram of BB Gem Table 9 O-C residuals for BB Gem Obs.Max.J.D. E O-C Type w Source 2425296.787 -7167 +0.012d phg 2 Zonn (1935) 2427482.659 -6220 +0.012 phg 2 Zonn (1935) 2428454.365 -5799 -0.038 vis 0.5 Solov'yov (1940) 2431425.091 -4512 +0.026 phg 1 Teplitskaya (1951) 2433315.399 -3693 -0.088 phg 0.5 Satyvaldiev (1970) 2433317.80 -3692 +0.01 phg 0.5 Solov'yov (1951) 2433421.608 -3647 -0.056 phg 0.5 Borzdyko (1964) 2434975.100 -2974 +0.013 phg 0.5 Borzdyko (1964) 2435157.412 -2895 -0.024 phg 0.5 Satyvaldiev (1970) 2436784.690 -2190 -0.032 phg 0.5 Borzdyko (1964) 2436800.905 -2183 +0.026 phg 0.5 Satyvaldiev (1970) 2436849.315 -2162 -0.036 phel 2 Oosterhoff (1960) 2437606.48 -1834 +0.04 phg 0.5 Ahnert (1963) 2438201.986 -1576 +0.025 phg 0.5 Satyvaldiev (1970) 2441839.711 0 +0.016 phel 3 present paper AU Pegasi This is usually classified as a Population II cepheid (Kukarkin et al. 1969-1970, Opolski 1968, Petit 1960). Several authors (Gascoigne and Eggen 1957, Kolesnik and Kheilo 1970) classified it among classical cepheids. The phase shift between the maxima of its light and colour curves as the only population criterion at the small amplitude cepheids based on optical observations unambiguously shows that AU Peg belongs to Population II (see Figure 13 V, B-V and U-B curves of AU Peg Fig. 13). Moreover, the strong changes in the period of AU Peg (see Fig. 14) also support this classification. The short period classical cepheids do not show such strong period changes. The O-C diagram shows an interesting structure. It was computed with the ephemeris: C = 2435801.832 + 2.390048d*E . I was unable to find a unique representation of the O-C diagram. At earlier epochs two different O-C residuals are listed and plotted for each maximum. It is hard to decide which curve is the real one. However, the light curves plotted from the observations serving as a basis for computing O-C values show less scatter when using the smaller value of the period, i.e. the upper curve is more suitable. This curve shows a continuous increase of the period, but it cannot be approximated with a parabola. The minimum value of the period was about 2.3844d at J.D. 2427000, the maximum value at present is 2.40142d. The total change of the period is about 1%. There are no other short period cepheids showing such a large period variation. For example, V1 in M15 has a quasi-parabolic O-C graph with considerable period change but the total change in its period is about 0.01% during 23000 days (Barlai 1977). The central part of the O-C diagram in Fig. 14 is in accordance with the O-C diagram published by Kwee (1967). Figure 14 O-C diagram of AU Peg Table 10 O-C residuals for AU Peg Obs.Max.J.D. E O-C Type w Source 2419080.201 ? ? phg 0.5 Parenago (1934) 2426578.959 -3863 +9.882d vis 0.5 Florya (1933) -3859 +0.322 2426636.40 -3839 +9.96 vis 0.5 Lause (1932) -3835 +0.40 2426952.911 -3706 +8.597 vis 0.5 Florya (1933) -3703 +1.427 2427000.90 -3686 +8.78 vis 0.5 Lause (1933) -3683 +1.61 2428729.76 -2961 +4.86 vis 0.5 Kukarkin (1938) -2960 +2.47 2433151.976 -1109 +0.709 phel 2 Eggen et al. (1957) 2433156.727 -1107 +0.678 phg 0.5 Vasil'yan. et al.^1 (1970) 2433875.952 -806 +0.499 phg 0.5 Vasil'yan. et al.^1 (1970) Table 10 (cont.) Obs.Max.J.D. E O-C Type w Source 2434258.118 -646 +0.257d phg 0.5 Vasil'yan. et al.^1 (1970) 2434614.133 -497 +0.155 phg 0.5 Vasil'yan. et al.^1 (1970) 2434654.90 -480 +0.29 phg 0.5 Gunther (1955) 2435383.768 -175 +0.194 phg 0.5 Vasil'yan. et al.^1 (1970) 2435667.965 - 56 -0.024 phel 3 Walraven et al. (1958) 2435751.615 - 21 -0.026 phg 0.5 Vasil'yan. et al.^1 (1970) 2436076.678 +115 -0.010 phg 0.5 Vasil'yan, et al.^1 (1970) 2436093.540 +122 +0.122 phg 0.5 Korovkina (1958) 2436442.493 +268 +0.128 phg 0.5 Vasil'yan. et al.^1 (1970) 2436829.821 +430 +0.268 phg 0.5 Vasil'yan. et al.^1 (1970) 2437185.841 +579 +0.171 phel 3 Mitchell et al. (1964) 2437207.539 +588 +0.359 phg 0.5 Vasil'yan. et al.^1 (1970) 2437580.286 +744 +0.258 phg 0.5 Vasil'yan. et al.^1 (1970) 2437941.154 +895 +0.229 phg 0.5 Vasil'yan. et al.^1 (1970) 2438228.339 +1015 +0.608 phel 3 Kwee and Braun (1967) 2438300.062 +1045 +0.630 phg 0.5 Vasil'yan. et al.^1 (1970) 2438654.026 +1193 +0.867 phg 0.5 Vasil'yan. et al.^1 (1970) 2439039.083 +1354 +1.126 phel 3 Wamsteker (1972) 2441739.439 +2481 +7.898 phel 3 present paper 2443031.402 +3019 +14.015 phel 2 present paper Remark: 1 Observer: Shakhovskaya DT Cygni This variable is a cepheid with small amplitude. The light and colour curves (Fig. 15) have no excess scatter in spite of the fact that the comparison star BD +29—4324 is included in the GCVS as the variable V 389 Cygni. For this reason the check star BD +30—4322 was observed at each observation of DT Cygni. The magnitude differences between the comparison and check stars indicate that one or other of the two stars varies. If the light curve of DT Cyg is constructed by using the magnitude differences between DT Cyg and the check star the scatter on the curve is much larger. Consequently, the check star BD +30—4322 is a suspected variable and V 339 Cyg has a constant light. The constancy of the comparison star V 389 Cyg was also checked by observing DT Cyg at almost the same phases on different nights. In order to determine the nature of light variation of this new suspected variable further observations of BD +30—4322 are planned. As to the O-C diagram of DT Cyg, a new interpretation of period changes of this cepheid is proposed (see Fig. 16). During long intervals (2000-4000 days) the period is constant and has the same value, whereas during the intermediate intervals the Table 11 O-C residuals for DT Cyg Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2424375.583 2424374.998 -6947 -1.087d -1.117d phel 3 Huffer (1928b) 2424695.538 -6819 -1.015 phel 2 Huffer (1928b) 2424785.340 -6783 -1.180 phg 1 Barabashev^1 (1928) 2425427.670 -6526 -1.114 vis 0.5 Kukarkin (1940) 2425802.466 -6376 -1.180 vis 0.5 Kukarkin (1940) 2425805.055 -6375 -1.090 vis 0.5 Zverev (1936) 2426047.562 -6278 -0.994 vis 0.5 Mustel' (1934) 2426344.978 -6159 -0.969 vis 0.5 Zverev (1936) 2426434.756 _ -6123 -1.156 vis 0.5 Kukarkin (1940) 2426922.178 -5928 -1.057 vis 0.5 Zverev (1936) 2427547.008 2427546.385 -5678 -0.997 -1.065 phel 2 Schneller (1936) 2427676.776 -5626 -1.182 vis 0.5 Krebs (1935) 2427976.728 -5506 -1.120 vis 0.5 Dziewulski (1962) 2428046.826 -5478 -0.996 vis 0.5 Krebs (19371) 2428466.617 -5310 -1.051 vis 1 Kepinski (1937) 2432975.319 24329.74.759 -3506 -0.693 -0.698 phel 2 Eggen (1951) 2433295.022 -3378 -0.872 vis 0 Dziewulski (1962) 2435259.67 -2592 -0.50 vis 1 Marks (1959) 2436099.527 -2256 -0.437 phel 2 Svolopoulos (1960) 2437176.700 2437176.118 -1825 -0.268 -0.295 phel 3 Mitchell et al. (1964) 2437579.091 2437578.504 -1664 -0.210 -0.162 phel 3 Johansen (1971) 2438496.241 2438495.722 -1297 -0.243 -0.207 phel 3 Johansen (1971) 2438871.112 2438870.575 -1147 -0.234 -0.216 phel 3 Wisniewski, Johnson (1968) 2441737.798 2441737.238 0 +0.005 0.000 phel 3 present paper 2443044.805 +523 -0.008 phel 2 present paper Remark: 1 Observer: Shemejkin. Figure 15 V, B-V and U-B curves of DT Cyg Figure 16 O-C diagram of DT Cyg moments of maxima are submitted to phase shifts. The values of these shifts are 0.21d - 0.23d or their multiple. This gradual period change is very interesting and it is intended to continue observations on DT Cygni. The O-C residuals given in Table 11 have been computed with the formulae: C_{max} = 2441737.793 + 2.499082d*E ; C_{med} = 2441737.238 + 2.499082d*E . It is worthy of note that a change of -3 km/s in normal radial velocity occurred between J.D. 2432000 and J.D. 2433000 (Evans 1968), i.e. during the time of a phase lag of the maximum. BE Monocerotis Its light and colour curves are shown in Fig. 17. The O-C residuals have been computed with the formula: C = 2441880.240 + 2.705510d*E . These residuals are plotted in Fig. 18. The period of BE Mon is constant. Figure 17 V and B-V curves of BE Mon Figure 18 O-C diagram of BE Mon Table 12 O-C residuals for BE Mon Obs.Max.J.D. E O-C Type w Source 2425506.624 -6052 +0.131d phg 0.5 Busch, Haussler (1963) 2425644.35 -6001 -0.12 phg 0.5 Ahnert^1 (1960) 2425974.73 -5879 -0.11 phg 0.5 Ahnert^1 (1960) 2426407.29 -5719 -0.14 phg 0.5 Ahnert^1 (1960) 2427124.38 -5454 -0.01 phg 0.5 Ahnert^1 (1960) 2427397.56 -5353 -0.08 phg 0.5 Ahnert^1 (1960) 2427516.83 -5309 +0.14 phg 0.5 Ahnert^2 (1960) 2427849.47 -5186 0.00 phg 0.5 Ahnert^3 (1960) 2427863.20 -5181 +0.21 vis 0.5 Kukarkin (1960) 2427892.751 -5170 -0.002 vis 1 Solov'yov (1952a) 2427914.34 -5162 -0.06 phg 0.5 Ahnert^2 (1960) 2428206.89 -5054 +0.30 phg 0 Ahnert^1 (1960) Table 12 (cont.) Obs.Max.J.D. E O-C Type w Source 2428260.667 -5034 -0.036 vis 1 Solov'yov (1952a) 2428547.40 -4928 -0.09 phg 0.5 Ahnert^1 (1960) 2429229.46 -4676 +0.18 phg 0.5 Ahnert^1 (1960) 2429313.305 -4645 +0.159 phg 0.5 Busch, Haussler (1963) 2429629.72 -4528 +0.03 phg 0.5 Ahnert^1 (1960) 2429667.572 -4514 +0.004 phg 1 Kapko (1963) 2429943.60 -4412 +0.07 phg 0.5 Ahnert^1 (1960) 2429989.503 -4395 -0.021 phg 1 Kapko (1963) 2430346.61 -4263 -0.04 phg 0.5 Ahnert^1 (1960) 2430698.52 -4133 +0.15 phg 0.5 Ahnert^1 (1960) 2430790.37 -4099 +0.02 phg 0.5 Ahnert^2 (1960) 2431050.14 -4003 +0.06 phg 0. Ahnert^3 (1960) 2431466.75 -3849 +0.02 phg 0. Ahnert^1 (1960) 2431986.169 -3657 -0.021 phg 1 Kapko (1963) 2432188.96 -3582 -0.14 phg 0.5 Ahnert^1 (1960) 2433306.47 -3169 -0.01 phg 0.5 Ahnert^2 (1960) 2433658.25 -3039 +0.05 phg 0.5 Ahnert^4 (1960) 2433934.10 -2937 -0.06 phg 0.5 Ahnert^5 (1960) 2434307.59 -2799 +0.07 phg 0.5 Ahnert^5 (1960) 2434778.38 -2625 +0.10 phg 0.5 Ahnert^5 (1960) 2435062.38 -2520 +0.03 phg 0.5 Ahnert^5 (1960) 2435143.551 -2490 +0.031 phg 1 Kapko (1963) 2435146.20 -2489 -0.03 phg 0.5 Ahnert^5 (1960) 2435395.06 -2397 -0.07 phg 0.5 Ahnert^2 (1960) 2435454.46 -2375 -0.19 phg 0.5 Ahnert (1960) 2435841.45 -2232 -0.09 phg 0.5 Ahnert^2 (1960) 2435860.367 -2225 -0.113 phg 0.5 Busch, Haussler (1963) 2436144.45 -2120 -0.11 phg 0.5 Ahnert^3 (1960) 2436612.62 -1947 +0.01 vis 1 Ahnert (1960) 2436615.44 -1946 +0.12 phg 0.5 Ahnert^1 (1960) 2436731.692 -1903 +0.038 phg 1 Kapko (1963) 2436899.56 -1841 +0.16 phg 0.5 Ahnert^2 (1960) 2436929.104 -1830 -0.053 phel 3 Detre, Chang (1960) 2437578.454 -1590 -0.025 phg 1 Ahnert (1963) 2438741.808 -1160 -0.040 phel 3 Buchancowa et al. (1972) 2441880.253 0 +0.013 phel 3 present paper Remarks: 1 Observer: Busch; 2 Obs.: Lochel; 3 Obs.: Busch and Lochel; 4 Obs.: Busch and Gotz; 5 Obs.: Busch, Gotz and Lochel; 6 Obs.: Gotz and Lochel; 7 Obs.: Gotz. V 465 Monocerotis This star is a cepheid with small amplitude (see Fig. 19). The O-C residuals have been calculated with the formula: C = 2441698.687 + 2.713176d*E . The O-C diagram plotted in Fig. 20 shows two period changes. Before J.D. 2432000 the value of the period was uncertain; between J.D. 2432000 and J.D. 2441600 , P = 2.713668d ; after J.D. 2441600 , P = 2.713176d. Figure 19 V and B-V curves of V 465 Mon Figure 20 O-C diagram of V 465 Mon Table 13 O-C residuals for V 465 Mon Obs.Max.J.D. E O-C Type w Source 2430025.3 -4302 -1.3d phg 0.5 Wachmann (1964) 2430421.308 -4156 -1.420 phg 0.5 Satyvaldiev (1970) 2431845.3 -3631 -1.8 phg 0.5 Wachmann (1964) 2432968.864 -3217 -1.536 phg 0.5 Satyvaldiev (1970) 2434040.646 -2822 -1.458 phg 0.5 Satyvaldiev (1970) 2434773.23 -2552 -1.43 phg 0.5 Wachmann (1964) 2435169.4 -2406 -1.4 phg 0.5 Wachmann (1964) 2435541.315 -2269 -1.176 phg 0.5 Satyvaldiev (1970) 2436632.053 -1867 -1.134 phg 0.5 Satyvaldiev (1970) 2438067.872 -1338 -0.586 phg 0.5 Satyvaldiev (1970) 2441698.687 0 0.000 phel 3 present paper 2443166.515 +541 0.000 phel 2 present paper BD +56—2806 Its variability was discovered by Fernie and Hube (1971); the first determination of its period was published by Szabados (1976b). The bump after the minimum light mentioned at the same Figure 21 V and B-V curves of BD +56—2806 paper may be not real. The light curve of BD +56—2806 is presented in Fig. 21. The O-C curve cannot be constructed for lack of earlier observations. The observations made by Percy (1975) were used to improve the value of the period determined from the present observations. The O-C residuals have been computed with the formula: C = 2442676.397 + 2.80591d*E . Table 14 O-C residuals for BD +56— 2806 Obs.Max.J.D. E O-C Type w Source 2442031.038 -230 0.000d phel 2 Percy (1975) 2442676.397 0 0.000 phel 3 present paper DX Geminorum This is a cepheid with small amplitude (see Fig. 22). The O-C residuals have been computed with the formula: C = 2441866.664 + 3.137486d*E . Figure 22 V and B-V curves of DX Gem Figure 23 O-C diagram of DX Gem Table 15 O-C residuals for DX Gem Obs.Max.J.D. E O-C Type w Source 2425295.158 -5283 +3.833d phg 1 Bartkus et al. (1961) 2426038.579 -5046 +3.669 phg 0.5 Bartkus et al. (1961) 2427449.718 -4596 +2.940 phg 0.5 Bartkus et al. (1961) 2427782.331 -4490 +2.979 phg 0.5 Bartkus et al. (1961) 2428594.596 -4231 +2.635 phg 1 Meshkova (1940) 2429638.790 -3898 +2.046 phg 0.5 Teplitskaya (1950) 2433182.876 -2768 +0.773 phg 1 Satyvaldiev (1970) 2434067.275 -2486 +0.401 phg 0.5 Satyvaldiev (1970) 2435413.021 -2057 +0.166 phg 1 Satyvaldiev (1970) 2435554.199 -2012 +0.157 phel 1 Walraven et al. (1958) 2435896.212 -1903 +0.184 phg 1 Bartkus et al. (1961) 2436275.716 -1782 +0.052 phg 1 Bartkus et al. (1961) 2436623.856 -1671 -0.069 phg 0.5 Satyvaldiev (1970) 2436815.042 -1610 -0.270 phg 0.5 Bartkus et al. (1961) 2437687.330 -1332 -0.203 phg 0.5 Satyvaldiev (1970) 2438744.322 -995 -0.543 phg 0 Satyvaldiev (1970) 2440793.641 -342 -0.003 phel 3 Pel (1976) 2441866.668 0 +0.004 phel 3 present paper 2443165.579 +414 -0.004 phel 2 present paper The O-C diagram (Fig. 23) shows two changes in the period. The first period change was also suspected by Bartkus and Puchinskas (1961). The following values of the period are valid for different time intervals: before J.D. 2434000, P = 3.136226d ; between J.D. 2434000 and J.D. 2436500, P = 3.136955d ; after J.D. 2436500, P = 3.137486d . SZ Tauri According to Kukarkin et al. (1974) SZ Tau is a possible member of the cluster NGC 1647. The phase relations of the colour curves (see Fig. 24) also support its belonging to Population I. However, several authors classified SZ Tau as a Population II variable (Walraven et al. 1958, Petit 1960, Mianes 1963, Kheilo 1969). According to Madore (1977), SZ Tau has a blue photometric companion. Figure 24 V, B-V and U-B curves of SZ Tau The O-C residuals have been derived using the formula: C = 2441659.194 + 3.14838d*E . The O-C diagram (Fig. 25) shows three changes in the period of SZ Tauri: before J.D. 2418500, P = 3.14839d ; between J.D. 2418500 and J.D. 2425500, P = 3.149235d ; between J.D. 2425500 and J.D. 2436300, P = 3.149057d ; after J.D. 2436300, P = 3.148380d . This O-C diagram shows an interesting phenomenon: at present the period of pulsation of SZ Tau is nearly identical with the value of the period which was valid several decades ago. Such a return Figure 25 O-C diagram of SZ Tau to an earlier period has been found for DT Cyg and other cepheids. A more detailed discussion of this phenomenon will be given in the next section. Table 16 O-C residuals for SZ Tau Obs.Max.J.D. E O-C Type w Source 2413671.947 -8888 -4.446d phg 0.5 Pickering (1914) 2416118.575 -8111 -4.109 phg 1 Pickering (1914) 2417179.596 -7774 -4.092 phg 1 Pickering (1914) 2418086.326 -7486 -4.095 phg 0.5 Pickering (1914) 2418713.005 -7287 -3.944 vis 1 Schwarzschild (1911) 2418829.399 -7250 -4.040 phg 1 Pickering (1914) 2419267.519 -7111 -3.545 phg 0 Robinson (1930) 2419758.445 -6955 -3.766 phg 0.5 Pickering (1914) 2423619.49 -5729 -2.63 vis 0.5 Nielsen (1941) 2424878.851 -5329 -2.626 vis 0.5 Kukarkin (1940) 2425225.378 -5219 -2.421 phg 1 Hellerich (1935) 2425231.729 -5217 -2.367 vis 0.5 Kukarkin (1940) 2425301.067 -5195 -2.293 vis 0.5 Collmann (1930) 2425530.856 -5122 -2.336 vis 0.5 Kukarkin (1940) Table 16 (cont.) Obs.Max.J.D. E O-C Type w Source 2425587.492 -5104 -2.370d vis 0.5 Zverev (1936) 2425934.028 -4994 -2.156 vis 0.5 Zverev (1936) 2425959.093 -4986 -2.278 vis 0.5 Terkan (1935) 2426119.843 -4935 -2.096 vis 0.5 Kukarkin (1940) 2426324.450 -4870 -2.133 vis 0.5 Zverev (1936) 2426440.993 -4833 -2.080 vis 0.5 Terkan (1935) 2426705.583 -4749 -1.954 vis 0.5 Kukarkin (1940) 2426781.131 -4725 -1.967 vis 0.5 Zverev (1936) 2426894.594 -4689 -1.846 phg 1 Kox (1935) 2429363.229 -3905 -1.541 phg 0.5 Koshkina (1963) 2432852.379 -2797 -0.796 phel 2 Eggen (1951) 2432858.695 -2795 -0.777 phg 0.5 Satyvaldiev (1970) 2433283.87 -2660 -0.63 vis 0.5 Pohl^1 (1950) 2433819.217 -2490 -0.511 phg 0.5 Koshkina (1963) 2434628.57 -2233 -0.29 vis 0.5 Marks^2 (1959) 2434776.562 -2186 -0.267 phg 1 Satyvaldiev (1970) 2435082.12 -2089 -0.11 vis 0.5 Marks (1959) 2435478.719 -1963 -0.205 vis 0.5 Azarnova (1957) 2435541.659 -1943 -0.233 phel 1 Walraven et al. (1958) 2435840.877 -1848 -0.111 vis 0.5 Azarnova (1960) 2435878.569 -1836 -0.199 phg 0.5 Satyvaldiev (1970) 2436162.052 -1746 -0.071 vis 0.5 Latyshev (1969) 2436206.061 -1732 -0.139 vis 0.5 Azarnova (1960) 2436574.589 -1615 +0.029 vis 0.5 Azarnova (1960) 2436766.632 -1554 +0.021 phg 0.5 Satyvaldiev (1970) 2437619.809 -1283 -0.013 phel 3 Mitchell et al. (1964) 2437962.988 -1174 -0.008 phel 1 Williams (1966) 2437969.481 -1172 +0.188 phg 0.5 Satyvaldiev (1970) 2438378.857 -1042 +0.275 phg 0.5 Satyvaldiev (1970) 2438529.659 -994 -0.045 phel 3 Wisniewski et al. (1968) 2439055.461 -827 -0.023 phel 3 Milone (1970) 2439077.600 -820 +0.078 phel 3 Wamsteker (1972) 2439807.965 -588 +0.018 phel 3 present paper^3 2441659.204 0 +0.010 phel 3 present paper Remarks: 1 Observer: Mielke; 2 Obs.: Wroblewski; 3 Obs.: Abaffy. DQ Andromedae This cepheid has not previously been observed photoelectrically. The presence of a bump on the descending branch 0.3p after the maximum can be suspected on the first photoelectric light curve (see Fig. 26). Classical cepheids with such a short period do not show bumps on their light curves. Moreover, the galactic latitude of DQ And is -18—. These two facts give reason to classify this cepheid as a Population II variable. The O-C residuals have been computed with the formula: C = 2441994.943 + 3.200557d*E . DQ And has a constant period during 8000 cycles (see Fig. 27). Figure 26 V and B-V curves of DQ And Figure 27 O-C diagram of DQ And Table 17 O-C residuals for DQ And Obs.Max.J.D. E O-C Type w Source 2416038.600 -8110 +0.174d phg 0.5 Strohmeier et al. (1968) 2416438.681 -7985 +0.186 phg 0.5 Strohmeier et al. (1968) 2416761.865 -7884 +0.113 phg 0.5 Strohmeier et al. (1968) 2417104.340 -7777 +0.129 phg 0.5 Strohmeier et al. (1968) 2417910.609 -7525 -0.143 phg 0.5 Strohmeier et al. (1968) 2418214.807 -7430 +0.003 phg 0.5 Strohmeier et al. (1968) 2418691.542 -7281 -0.145 phg 0.5 Strohmeier et al. (1968) 2419053.468 -7168 +0.118 phg 0.5 Strohmeier et al. (1968) 2419306.261 -7089 +0.067 phg 0.5 Strohmeier et al. (1968) 2419987.914 -6876 +0.001 phg 0.5 Strohmeier et al. (1968) 2420468.147 -6726 +0.150 phg 0.5 Strohmeier et al. (1968) 2422257.255 -6167 +0.147 phg 0.5 Strohmeier et al. (1968) 2422666.599 -6039 -0.180 phg 0.5 Strohmeier et al. (1968) 2423044.580 -5921 +0.135 phg 0.5 Strohmeier et al. (1968) 2423322.750 -5834 -0.143 phg 0.5 Strohmeier et al. (1968) Table 17 (cont.) Obs.Max.J.D. E O-C Type w Source 2423758.055 -5698 -0.114 phg 0.5 Strohmeier et al. (1968) 2424788.747 -5376 -0.002 phg 0.5 Strohmeier et al. (1968) 2425825.770 -5052 +0.041 phg 0.5 Strohmeier et al. (1968) 2426651.375 -4794 -0.098 phg 0.5 Strohmeier et al. (1963) 2426654.712 -4793 +0.039 phg 0.5 Strohmeier et al. (1968) 2426987.516 -4689 -0.015 phg 0.5 Strohmeier et al. (1963) 2427397.279 -4561 +0.076 phg 0.5 Strohmeier et al. (1963) 2427665.853 -4477 -0.196 phg 0.5 Strohmeier et al. (1968) 2428043.819 -4359 +0.104 phg 0.5 Strohmeier et al. (1968) 2428069.427 -4351 +0.108 phg 0.5 Strohmeier et al. (1963) 2428408.537 -4245 -0.042 phg 0.5 Strohmeier et al. (1963) 2428818.289 -4117 +0.039 phg 0.5 Strohmeier et al. (1968) 2429240.546 -3985 -0.177 phg 0.5 Strohmeier et al. (1968) 2429567.324 -3883 +0.144 phg 0.5 Strohmeier et al. (1968) 2429912.686 -3775 -0.154 phg 0.5 Strohmeier et al. (1968) 2430641.964 -3547 -0.603 vis 0 Tsessevitsch (1957) 2431055.586 -3418 +0.147 phg 0.5 Strohmeier et al. (1968) 2431439.406 -3298 -0.100 phg 0.5 Strohmeier et al. (1968) 2432092.556 -3094 +0.136 phg 0.5 Strohmeier et al. (1963) 2433177.339 -2755 -0.069 phg 2 Satyvaldiev (1970) 2433183.656 -2753 -0.154 phg 0.5 Strohmeier et al. (1968) 2433532.810 -2644 +0.140 phg 0.5 Strohmeier et al. (1968) 2433865.814 -2540 +0.286 phg 0.5 Strohmeier et al. (1968) 2433926.387 -2521 +0.038 phg 0.5 Strohmeier et al. (1963) 2434252.475 -2419 -0.321 phg 0.5 Strohmeier et al. (1963) 2434707.274 -2277 -0.001 phg 0.5 Strohmeier et al. (1963) 2435766.931 -1946 +0.272 phg 0.5 Wenzel, Ziegler (1965) 2435779.332 -1942 -0.129 phg 0.5 Strohmeier et al. (1963) 2436320.362 -1773 +0.007 phg 2 Satyvaldiev (1970) 2436509.252 -1714 +0.064 phg 0.5 Wenzel, Ziegler (1965) 2436825.965 -1615 -0.078 phg 0.5 Wenzel, Ziegler (1965) 243T232.522 -1488 +0.008 phg 0.5 Wenzel, Ziegler (1965) 2437245.363 -1484 +0.047 phg 0.5 Strohmeier et al. (1963) 2437610.445 -1370 +0.265 phg 0.5 Wenzel, Ziegler (1965) 2437933.503 -1269 +0.067 phg 0.5 Wenzel, Ziegler (1965) 2438295.081 -1156 -0.018 phg 2 Satyvaldiev (1970) 2438295.102 -1156 +0.003 phg, 0.5 Wenzel, Ziegler (1965) 2438432.689 -1113 -0.034 phg 0.5 Wenzel, Ziegler (1965) 2441994.950 0 +0.007 phel 3 present paper BY Cassiopeiae BY Cas is a cepheid with small amplitude (see Fig. 28). Its period shows large variations. As can be seen from Fig. 29, the period of BY Cas has had the following values: between J.D. 2417000 and J.D. 2426900 there was a change in the period, but both the time of the change and the value of the period in this interval are unknown; between J.D. 2426900 and J.D. 2434300, P = 3.221297d ; between J.D. 2434300 and J.D. 2439400, P = 3.222588d ; after J.D. 2439400, P = 3.223316d . Figure 28 V and B-V curves of BY Cas Figure 29 O-C diagram of BY Cas The O-C residuals have been computed with the formulae: C_{max} = 2441774.191 + 3.223316d*E ; C_{med} = 2441773.408 + 3.223316d*E . Table 18 O-C residuals for BY Cas Obs.Max.J.D. Obs.Med.J.D. E O-C O-S Type w Source max med 2417068.714 -7667 +7.687d phg 1 Kukarkina (1954a) 2426933.30 -4606 +5.70 vis 1 Lange (1933) 2428563.344 -4100 +4.749 phg 1 Parenago (1939b) 2429223.824 -3895 +4.449 phg 1 Kukarkina (1954a) 2430480.163 -3505 +3.695 phg 1 Satyvaldiev (1970) 2430650.693 -3452 +3.389 phg 1 Dirks, Vaucouleurs (1949) 2431014.735 -3339 +3.196 phg 1 Satyvaldiev (1970) 2431781.53 -3101 +2.84 phg 1 Ashbrook (1954) 2432048.696 -3018 +2.473 phg 1 Dirks, Vaucouleurs (1949) 2432132.390 -2992 +2.360 phg 1 Satyvaldiev (1970) 2433524.24 -2560 +1.74 phg 1 Satyvaldiev (1970) 2433736.708 -2494 +1.467 phg 1 Kukarkina (1954a) 2433878.46 -2450 +1.39 phg 1 Ashbrook (1954) 2434361.768 -2300 +1.204 phg 1 Kheilo (1962) 2435557.258 -1929 +0.844 phg 1 Kheilo (1962) 2435615.515 -1911 +1.081 phg 1 Satyvaldiev (1970) 2436143.784 -1747 +0.716 phg 1 Kheilo (1962) 2436820.545 2436819.781 -1537 +0.591 +0.610 phel 3 Oosterhoff (1960) 2436827.004 2436826.233 -1535 +0.603 +0.615 phel 3 Weaver et al. (1960) 2436843.175 -1530 +0.657 phg 1 Kheilo (1962) 2436910.801 2436910.027 -1509 +0.594 +0.603 phel 3 Bahner et al. (1962) 2438248.220 -1094 +0.337 phg 1 Satyvaldiev (1970) 2438409.256 2438408.479 -1044 +0.207 +0.213 phel 3 Malik (1965) 2438660.818 -966 +0.350 phg 1 Satyvaldiev (1970) 2439785.406 2439784.636 -617 +0.001 +0.014 phel 3 present paper^1 2441774.189 2441773.395 0 -0.002 -0.013 phel 3 present paper 2443079.635 +405 +0.001 phel 2 present paper Remark: 1 Observer: Abaffy V 532 Cygni This small amplitude cepheid is suspected as having a blue photometric companion (Madore 1977). Its light and colour curves and O-C diagram are shown in Figs. 30 and 31, respectively. The Figure 30 V and B-V curves of V 532 Cyg Figure 31 O-C diagram of V 532 Cyg O-C residuals have been calculated with the elements: C = 2441706.559 + 3.283612d*E . The following values of the period are valid in the different time intervals: between J.D. 2428000 and J.D. 2435000, P = 3.283651d ; between J.D. 2435000 and J.D. 2438700, P = 3.282792d ; after J.D. 2438700, P = 3.283612d . The structure of this O-C diagram resembles that of SZ Tauri, i.e. the period has returned to its earlier value. Table 19 O-C residuals for V 532 Cyg Obs.Max.J.D. E O-C Type w Source 2428343.3 -4070 +1.0d phg 0.5 Ahnert (1949) 2428779.8 -3937 +0.8 phg 0.5 Ahnert (1949) 2428832.342 -3921 +0.826 phg 0.5 Ishchenko (1950) Table 19 (cont.) Obs.Max.J.D. E O-C Type w Source 2429058.993 -3852 +0.907d phg 0.5 Ishchenko (1950) 2429140.9 -3827 +0.7 phg 0.5 Ahnert (1949) 2429452.989 -3732 +0.870 phg 0.5 Ishchenko (1950) 2429571.2 -3696 +0.9 phg 0.5 Ahnert (1949) 2429860.182 -3608 +0.895 phg 0.5 Ishchenko (1950) 2429984.9 -3570 +0.8 phg 0.5 Ahnert (1949) 2430260.8 -3486 +0.9 phg 0.5 Ahnert (1949) 2430447.883 -3429 +0.830 phg 0.5 Filin (1951) 2430956.887 -3274 +0.874 phg 0.5 Filin (1951) 2431265.733 -3180 +1.060 phg 0.5 Filin (1951) 2431643.365 -3065 +1.077 phg 0.5 Filin (1951) 2431991.211 -2959 +0.860 phg 0.5 Filin (1951) 2432710.549 -2740 +1.087 phg 0.5 Filin (1951) 2433889.147 -2381 +0.868 phg 1 Shteiman (1958) 2434434.284 -2215 +0.926 phg 1 Shteiman (1958) 2435642.491 -18.47 +0.763 phg 1 Shteiman (1958) 2436092.219 -1710 +0.637 phg 0.5 Korovkina (1958) 2436443.59 -1603 +0.66 phg 0.5 Korovkina (1959) 2436817.703 -1489 +0.442 phel 3 Oosterhoff (1960) 2438229.332 -1059 +0.118 phel 3 Kwee and Braun (1967) 2441706.559 0 0.000 phel 3 present paper 2443026.571 +402 0.000 phel 2 present paper V 1334 Cygni This cepheid is a component of a visual binary (Millis 1969). The nonvariable component of this binary system reduces the observable amplitude of the cepheid. Figure 32 shows that the light and colour amplitudes of V 1334 Cyg are extremely low for a cepheid variable. The O-C residuals have been computed with the formula: C = 2441760.900 + 3.333020d*E These residuals are not plotted in a diagram. Figure 32 V, B-V and U-B curves of V 1334 Cyg Table 20 O-C residuals for V 1334 Cyg Obs.Max.J.D. E O-C Type w Source 2440117.721 -493 0.000d phel 3 Millis (1969) 2441760.900 0 0.000 phel 3 present paper BD Cassiopeiae BD Cas is a cepheid with small amplitude. There is a bump on its light curve just after the minimum (see Fig. 33). Therefore it has been classified as a Population II variable. Figure 34 O-C diagram of BD Cas The O-C residuals have been calculated with the formula: C = 2441932.032 + 3.650900d*E . The O-C curve (Fig. 34) consists of two straight lines. The values of the period are as follows: before J.D. 2429000, P = 3.65126 ; after J .D. 2429000, P = 3.650900 . Table 21 O-C residuals for BD Cas Obs.Max.J.D. E O-C Type w Source 2415038.2 -7366 -1.3d phg 0.5 Parenago (1947) 2417064.6 -6811 -1.2 phg 0.5 Parenago (1947) 2418926.8 -6301 -0.9 phg 0.5 Parenago (1947) 2427883.7 -3848 +0.3 phg 0.5 Parenago (1947) 2428573.8 -3659 +0.4 phg 0.5 Parenago (1947) 2428759.4 -3608 -0.2 vis 0.5 Zverev (1938) 2429124.84 -3508 +0.17 vis 1 Zverev (1938) 2429285.3 -3464 0.0 phg 0.5 Parenago (1947) 2429548.2 -3392 0.0 phg 0.5 Parenago (1947) 2430260.16 -3197 +0.06 phg 0.5 Vasil'yan. et al. (1970) 2430614.5 -3100 +0.3 phg 0.5 Parenago (1947) 2430643.19 -3092 -0.26 phg 0.5 Vasil'yan. et al. (1970) 2430939.33 -3011 +0.16 phg 0.5 Vasil'yan. et al. (1970) 2431300.34 -2912 -0.27 phg 0.5 Vasil'yan. et al. (1970) 2432768.38 -2510 +0.11 phg 0.5 Vasil'yan. et al. (1970) 2433118.82 -2414 +0.06 phg 0.5 Vasil'yan. et al. (1970) 2433863.38 -2210 -0.16 phg 0.5 Vasil'yan. et al. (1970) 2434962.32 -1909 -0.14 phg 0.5 Vasil'yan. et al. (1970) 2435042.57 -1887 -0.21 phg 1 Romano (1959) 2435430.02 -1781 +0.24 phg 1 Romano (1959) 2435670.77 -1715 +0.03 phg 1 Romano (1959) 2435700.33 -1707 +0.38 phg 0.5 Vasil'yan. et al. (1970) 2435835.18 -1670 +0.15 phg 1 Zonn, Semeniuk (1959) 2437211.28 -1293 -0.14 phg 0.5 Vasil'yan. et al. (1970) 2437525.27 -1207 -0.13 phg 0.5 Vasil'yan. et al. (1970) 2437572.843 -1194 -0.014 phel 1 Mitchell et al. (1964) 2438055.15 -1062 +0.37 phg 0.5 Vasil'yan. et al. (1970) 2438650.28 -899 +0.41 phg 0.5 Vasil'yan. et al. (1970) 2441931.916 0 -0.116 phel 3 present paper RT Aurigae Very many photoelectric observational series have been carried out on this star. The sets of photoelectric observations made in the UBV system do not verify the statement of the 3rd Supplement to the GCVS (Kukarkin et al. 1976), according to which the amplitude in V varies between 0.73m and 0.85m . As Table 22 shows, A_V varies between 0.76m and 0.83m, whereas A_B between 1.10m and 1.19m. However, these amplitude variations are not real. The light curves with extreme values of the amplitude are rather uncertain around the maximum. For example, the maximum amplitude is based upon a single observation of the light curve observed by Winzer (1973). The well observed light curves (Wisniewski and Johnson 1968, and the present paper) have almost the same values for the amplitudes. Moreover, the variation in the amplitudes does not show any systematic trend. Table 23 O-C residuals for RT Aur Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2414000.60 -7436 -0.25d vis 1 Muller, Kempf (1899) 2416938.466 -6648 -0.202 vis. 0.5 Astbury (1905) 2416942.3 -6647 -0.1 vis 0.5 Williams (1905a) 2417643.048 -6459 -0.248 vis 0.5 Zeipel (1908) 2417788.484 2417788.100 -6420 -0.211 -0.167 vis 1 Wendell (1913) 2417889.20 -6393 -0.16 vis 1 Kukarkin^1 (1931a) 2418015.92 -6359 -0.19 vis 1 Kukarkin^1 (1931a) 2418344.03 -6271 -0.17 vis 1 Kukarkin^1 (1931a) 2418739.18 -6165 -0.20 vis 1 Kukarkin^1 (1931a) 2418921.974 -6116 -0.091 phg 0.5 Robinson (1930) 2419044.99 -6083 -0.105 vis 0.5 Kukarkin^1 (1931a) 2419421.48 -5982 -0.16 vis 1 Hornig (1915) 2419451.27 -5974 -0.20 vis 1 Kukarkin^1 (1931a) 2419689.908 2419689.502 -5910 -0.164 -0.142 vis 1 Lacchini (1921) 2419813.015 2419812.627 -5877 -0.087 -0.047 vis 0.5 Nijland (1923) 2419824.13 -5874 -0.16 vis 1 Kukarkin^1 (1931a) 2419902.26 -5853 -0.32 vis 0.5 Kaiser (1922) 2420129.921 2420129.425 -5792 -0.078 -0.146 vis 1 Nijland (1923) 2420133.623 -5791 -0.104 vis 0.5 Hoffmeister (1915) 2420375.871 2420375.528 -5726 -0.188 -0.103 phg 2 Kiess (1915) 2420495.43 -5694 +0.07 vis 0 Kukarkin^1 (1931a) 2420502.691 2420502.266 -5692 -0.127 -0.124 vis 1 Nijland (1923) 2420972.434 2420972.042 -5566 -0.135 -0.100 vis 1 Nijland (1923) 2420991.000 2420990.680 -5561 -0.210 -0.102 vis 1 Luyten (1922) 2421475.879 2421475.417 -5431 +0.004 -0.030 vis 0.5 Lacchini (1921) 2421565.231 2421564.925 -5407 -0.121 +0.001 vis 1 Luyten (1922) 2422728.38 -5095 -0.17 vis 0.5 Viaro (1921) 2422739.73 -5092 0.00 vis 0.5 Kukarkin^2 (1931a) 2423112.38 -4992 -0.17 vis 0.5 Kukarkin^1 (1931a) 2423239.209 -4958 -0.100 vis 0.5 Stromgren^3 (1928) 2423272.767 2423272.331 -4949 -0.096 -0.104 vis 1 Hellerich (1934) 2423351.18 -4928 +0.03 vis 1 Kukarkin^4 (1931a) 2423791.110 -4810 +0.029 vis 0.5 Hopmann (1926b) 2423999.770 2423999.360 -4754 -0.090 -0.072 vis 1 Hellerich (1934) Table 23 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2424361.434 2424360.957 -4657 -0.060d -0.109d phg 1 Kowalczewsky (1931) 2424741.657 2424741.243 -4555 -0.113 -0.099 vis 1 Kukarkin (1940) 2425155.509 2425155.114 -4444 -0.090 -0.057 phg 2 Hellerich (1935) 2425293.462 2425293.000 -4407 -0.080 -0.114 vis 1 Kukarkin (1940) 2425535.844 2425535.475 -4342 -0.030 +0.029 vis 1 Zverev (1936) 2425744.619 2425744.198 -4286 -0.034 -0.027 vis 1 Kukarkin^5 (1940) 2425990.618 -4220 -0.095 vis 0.5 Kukarkin (1934) 2426232.946 2426232.551 -4155 -0.100 -0.067 vis 1 Zverev (1936) 2426400.773 -4110 -0.041 vis 1 Mergentaler (1941) 2426467.859 -4092 -0.063 vis 1 Nielsen (1939) 2426475.364 -4090 -0.014 vis 1 Kowalczewsky^6 (1931) 2426520.023 2426519.542 -4078 -0.093 -0.146 vis 0.5 Kukarkin (1940) 2426587.221 2426586.818 -4060 -0.004 +0.022 vis 1 Dufay (1947b) 2426911.538 2426911.169 -3973 -0.038 +0.021 phg 2 Grouillier (1947) 2427325.424 2427325.017 -3862 +0.019 +0.040 vis 1 Dufay (1947b) 2427452.125 2427451.752 -3828 -0.039 +0.016 phg 2 Grouillier (1947) 2427687.013 2427686.633 -3765 -0.027 +0.021 vis 1 Krebs (1937b) 2428358.074 2428357.686 -3585 -0.040 0.000 vis 1 Krebs (1937b) 2429070.198 2429069.769 -3394 0.000 -0.001 phg 2 Opolski (1948) 2429267.393 -3341 +0.029 phel 3 Bennett (1941) 2429603.272 -3251 -0.057 phel 3 Bennett (1941) 2433141.392 2433140.952 -2302 +0.010 -0.002 phel 3 Eggen et al. (1957) 2434539.42 -1927 -0.03 vis 0.5 Marks^7 (1959) 2435057.79 -1788 +0.12 vis 0.5 Marks (1959) 2435799.601 2435799.198 -1589 +0.020 +0.045 phel 3 Prokof'eva (1961) 2437339.350 -1176 +0.026 phel 3 Mitchell et al. (1964) 2437872.454 -1033 -0.001 vis 0.5 Tsai (1972) 2437995.423 -1000 -0.062 phel 2 Williams (1966) 2438920.047 2438919.618 -752 -0.029 -0.030 phel 3 Wisniewski, Johnson (1968) 2439359.960 2439359.505 -634 -0.043 -0.070 phel 3 Takase (1969) 2441429.115 2441428.757 -79 -0.033 +0.037 phel 3 Winzer (1973) 2441723.711 2441723.282 0 +0.036 +0.035 phel 3 present paper 2441761.14 +10 +0.18 vis 0.5 Small (1973) Remarks: 1 Observer: Sharbe; 2 Obs.: Tsarevsky, Tsessevitsch, Selivanov; 3 Obs.: Johansen; 4 Obs.: Tsessevitsch; 5 Obs.: Zverev; 6 Obs.: Dziewulski, Iwanowska; 7 Obs.: Wroblewski. Figure 35 V, B-V and U-B curves of RT Aur Table 22 Year A_V A_B Source 1961 0.77m: 1m13: Mitchell et al. (1964) 1965 0.80 1.18 Wisniewski, Johnson (1968) 1966 0.76: 1.10: Takase (1969) 1972 0.83: 1.19: Winzer (1973) 1973 0.81 1.17 present paper The light and colour curves based on the new observations are shown in Fig. 35. The small bump before the minimum light seems to be unreal. It appears in V light only, and the earlier photoelectric observations do not show such a bump at that phase. However, according to Winzer (1973), small fluctuations with amplitude of 0.02m - 0.04m may occur on the light curve. The O-C residuals have been computed with the formulae: C_{max} = 2441723.675 + 3.728190d*E ; C_{med} = 2441723.247 + 3.728190d*E . As the O-C diagram (Fig. 36) shows, the period has changed on one occasion: before J.D. 2430000, P = 3.728243d ; after J.D. 2430000, P = 3.728190d . Figure 36 O-C diagram of RT Aur V 572 Aquilae According to the 2nd Supplement to the GCVS (Kukarkin et al. 1974) its period and form of the light curve vary. However, the present observations have shown (see Fig. 37) that the light curve is stable and very similar to earlier published ones if the observations are plotted with the correct period. Though the present observations were made in two colours, the U-B colour curve of V 572 Aql is available from the observations made by Oosterhoff (1960). The phase relation between the minimum values of U-B and B-V colour indices and the relatively large distance of this variable from the galactic plane (b = -15.5—) give reason to classify V 572 Aql as a Population II cepheid. Figure 37 V and B-V curves of V 572 Aql Figure 38 O-C diagram of V 572 Aql The O-C residuals have been calculated with the formula: C = 2441921.259 + 3.767697d*E . For the time before J.D.2435500 the value of the period is rather uncertain (about 3.7686d). After J.D. 2435500 the period is 3.767697d (see Fig. 38). Table 24 O-C residuals for V 572 Aql Obs.Max.J.D. E O-C Type w Source 2428397.31 -3589 -1.68d vis 0.5 Solov'yov (1.944) 2433171.77 -2322 -0.90 phg 0.5 Vasil'yan. et al.^1 (1970) 2433911.20 -2126 +0.06 phg 0.5 Vasil'yan. et al.^1 (1970) 2434660.20 -1927 -0.71 phg 0.5 Vasil'yan. et al.^1 (1970) 2435666.856 -1660 -0.026 phel 3 Walraven et al. (1958) 2435723.24 -1645 -0.16 phg 0.5 Vasil'yan. et al.^1 (1970) 2436036.15 -1562 +0.03 phg 0.5 Vasil'yan. et al.^1 (1970) 2436398.33 -1466 +0.51 phg 0 Vasil'yan. et al.^1 (1970) 2436789.776 -1362 +0.120 phel 3 Oosterhoff (1960) 2436801.28 -1359 +0.32 phg 0.5 Vasil'yan. et al.^1 (1970) 2437079.42 -1285 -0.35 phg 0.5 Vasil'yan. et al.^1 (1970) 2437908.34 -1065 -0.32 phg 0.5 Vasil'yan. et al.^1 (1970) 2438229.34 -980 +0.42 phg 0.5 Vasil'yan. et al.^1 (1970) 2438971.43 -783 +0.28 phg 0.5 Vasil'yan. et al.^1 (1970) 2441921.259 0 0.000 phel 3 present paper Remark: Observer: Satyvaldiev AD Geminorum The light and colour curves of this variable are shown in Fig. 39. The O-C residuals have been calculated with the formula: C = 2441694.911 + 3.787980d*E . The period has remained constant since the discovery of the light variation of AD Gem (see Fig. 40). Figure 39 V and B-V curves of AD Gem Figure 40 O-C diagram of AD Gem Table 25 O-C residuals for AD Gem Obs.Max.J.D. E O-C Type w Source 2420410.450 -5619 +0.199d phg 0.5 Kukarkin (1930b) 2422031.507 -5191 0.000 phg 1 Kukarkina (1954b) 2424963.453 -4417 +0.050 phg 1 Prager (1929) 2426065.669 -4126 -0.037 vis 1 Beyer (1934a) 2427084.676 -3857 +0.004 vis 1 Beyer (1934a) 2428065.750 -3598 -0.009 vis 0.5 Martynov (1951) 2428558.196 -3468 0.000 vis 0.5 Martynov (1951) 2428899.045 -3378 -0.070 vis 0.5 Martynov (1951) 2429274.075 -3279 -0.050 vis 0.5 Martynov (1951) 2429611.295 -3190 +0.040 vis 0.5 Martynov (1951) 2429993.989 -3089 +0.148 vis 0.5 Martynov (1951) 2430395.357 -2983 -0.010 vis 0.5 Martynov (1951) 2430853.685 -2862 -0.027 vis 0.5 Martynov (1951) 2432081.011 -2538 -0.007 phg 1 Kukarkina (1954b) Table 25 (cont.) Obs.Max.J.D. E O-C Type w Source 2436778.167 -1298 +0.054d phg 0.5 Huth (1963a) 2436834.942 -1283 +0.009 phel 2 Weaver et al. (1960) 2437524.267 -1101 -0.078 phg 1 Fridel' (1971) 2437630.387 -1073 -0.021 phel 3 Mitchell et al. (1964) 2438475.042 -850 -0.086 phg 1 Fridel' (1971) 2439202.459 -658 +0.039 phel 3 Takase (1969) 2441694.948 0 +0.037 phel 3 present paper DF Cassiopeiae The light and colour curves of DF Cas are shown in Fig. 41. The O-C residuals have been computed with the formula: C = 2441719.622 + 3.832472d*E . The O-C diagram (Fig. 42) can be represented by a straight line, i.e. the period is constant. Figure 41 V and B-V curves of DF Cas Table 26 O-C residuals for DF Cas Obs.Max.J.D. E O-C Type w Source 2417648.066 -6281 +0.201d phg 1 Perova (1954) 2428562.672 -3433 -0.074 phg 1 Meshkova (1940) 2428873.207 -3352 +0.031 phg 1 Perova (1954) 2432019.605 -2531 -0.030 phg 1 Perova (1954) 2433774.741 -2073 -0.167 phg 1 Perova (1954) 2434299.952 -1936 -0.004 phg 1 Perova (1954) 2436905.985 -1256 -0.052 phel 3 Bahner et al. (1962) 2437630.389 -1067 +0.015 phel 2 Mitchell et al. (1964) 2441719.659 0 +0.037 phel 3 present paper 2443149.118 +373 -0.016 phel 2 present paper Figure 42 O-C diagram of DF Cas SU Cygni Its light and colour curves are typical of classical cepheids (see Fig. 43), nevertheless Kolesnik and Kheilo (1970) doubted this classification. According to Madore (1977), SU Cyg has a blue photometric companion. Figure 43 V, B-V and U-B curves of SU Cyg The O-C residuals have been computed with the formulae: C_{max} = 2441778.935 + 3.845492d*E ; C_{med} = 2441778.589 + 3.845492d*E . As Fig. 44 shows, a sudden period change took place at about J.D. 2430000 . After a short time the value of the period returned to its original. This phenomenon is similar to that mentioned for DT Cyg, SZ Tau and V 532 Cyg. This "rejumping" period is even more interesting because the O-C diagram for the median brightness could be also constructed. This latter O-C diagram Table 27 O-C residuals for SU Cyg Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2414256.621 -7157 -0.128d vis 1 Muller, Kempf (1897) 2414441.3 -7109 0.0 vis 0.5 Muller, Hartwig^1 (1920) 2414491.161 -7096 -0.163 vis 1 Zinner^1 (1932) 2414564.221 -7077 -0.167 vis 1 Luizet (1899) 2414591.118 2414590.722 -7070 -0.189 -0.239d vis 1 Wendell (1913) 2414864.138 -6999 -0.198 vis 1 Prittwitz (1901) 2414906.20 -6988 -0.44 vis 0 Yendell (1900) 2414986.89 -6967 -0.50 vis 0 Yendell^2 (1902b) 2415079.481 -6943 -0.203 vis 1 Zinner^1 (1932) 2415236.85 -6902 -0.50 vis 0 Yendell (1902a) 2415606.573 -6806 +0.057 vis 0 Luizet (1907) 2415663.71 -6791 -0.39 vis 0 Yendell (1902a) 2415748.613 -6769 -0.187 vis 0.5 Zinner^1 (1932) 2415940.97 -6719 -0.10 vis 0.5 Yendell (1905) 2415956.4 -6715 -0.10 vis 0.5 Muller, Hartwig^1 (1920) 2415968.020 -6712 +0.027 vis 0.5 Luizet (1907) 2416337.155 -6616 -0.005 vis 0.5 Luizet (1907) 2416690.815 -6524 -0.130 vis 0.5 Luizet (1907) 2416848.454 -6483 -0.156 vis 1 Prittwitz (1907) 2417052.191 2417051.794 -6430 -0.230 -0.281 phg 2 Wilkens (1906) 2417079.313 -6423 -0.027 vis 0.5 Luizet (1907) 2417086.3 -6421 -0.7 vis 0 Maddrill (1906) 2417367.769 -6348 +0.017 vis 0.5 Luizet (1907) 2417829.048 2417828.641 -6228 -0.163 -0.224 vis 1 Zeipel (1908) 2417882.822 -6214 -0.226 vis 1 Van der Bilt (1925) 2418175.117 -6138 -0.188 vis 1 Van der Bilt (1925) 2418528.908 -6046 -0.182 vis 1 Van der Bilt (1925) 2419271.104 -5853 -0.166 vis 1 Van der Bilt (1925) 2421086.203 -5381 -0.140 vis 1 Luyten (1922) 2421278.435 -5331 -0.182 phg 0.5 Robinson (1931b) 2421443.751 -5288 -0.222 vis 1 Luyten (1922) 2421943.616 -5158 -0.271 vis 1 Luyten (1922) 2422582.072 -4992 -0.167 vis 0.5 Doberck (1925) 2423308.866 -4803 -0.171 vis 0.5 Doberck (1925) Table 27 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2423320.515 -4800 -0.058d vis 1 Hellerich (1925) 2423658.842 -4712 -0.135 vis 0.5 Doberck (1925) 2423662.684 -4711 -0.138 vis 1 Hellerich (1925) 2424012.510 -4620 -0.252 vis 0.5 Parenago (1938) 2424028.020 -4616 -0.124 vis 1 Hellerich (1925) 2424738.969 -4431 -0.245d vis 1 Moncibowitz^3 (1938) 2424816.453 -4411 -0.017 vis 0.5 Kukarkin (1940) 2425100.868 2425100.518 -4337 -0.168 -0.171 phg 2 Hellerich (1935) 2425131.234 -4329 -0.220 vis 1 Moncibowitz^3 (1938) 2425147.039 -4325 -0.143 vis 0.5 Kukarkin (1940) 2425243.24 -4300 -0.08 vis 0.5 Lause (1938) 2425323.499 -4279 -0.230 vis 1 Moncibowitz^3 (1938) 2425462.388 -4243 -0.124 vis 0.5 Kukarkin (1940) 2425696.940 2425696.552 -4182 -0.147 -0.189 vis 1 Zverev (1936) 2425804.661 -4154 -0.100 vis 0.5 Kukarkin (1940) 2425835.346 -4146 -0.179 vis 0.5 Parenago (1938) 2425904.749 -4128 +0.005 phg 0.5 Nassau, Townson (1932) 2426342.945 -4014 -0.185 vis 0.5 Kukarkin (1940) 2426423.739 -3993 -0.146 vis 1 Zverev (1936) 2426619.822 -3942 -0.184 vis 0.5 Kukarkin (1940) 2426908.262 -3867 -0.155 vis 0.5 Dziewulski et al. (1946) 2426923.669 -3863 -0.130 vis 1 Florya, Kukarkina (1953) 2427277.410 2427277.010 -3771 -0.175 -0.229 vis 1 Florya, Kukarkina (1953) 2427677.322 2427676.857 -3667 -0.194 -0.313 vis 1 Krebs (1935) 2427754.297 -3647 -0.129 vis 0.5 Dziewulski et al. (1946) 2427861.865 -3619 -0.234 vis 0.5 Miczaika (1937) 2428050.410 -3570 -0.119 vis 1 Krebs (1937a) 2428758.046 -3386 -0.053 phg 0.5 Dziewulski et al. (1946) 2429057.958 -3308 -0.089 phg 0.5 Kholopov (1947) 2429523.285 -3187 -0.067 vis 0.5 Remenchiz (1946) 2430238.647 -3001 +0.033 vis 0.5 Lochel^4 (1964) 2430588.687 -2910 +0.134 vis 0.5 Lochel^4 (1964) 2432861.300 -2319 +0.061 phg 0.5 Wachmann (1966) 2433126.659 -2250 +0.081 phel 3 Eggen (1951) 2433472.65 -2160 -0.02 vis 0.5 Domke, Pohl^5 (1952) Table 27 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2433538.118 -2143 +0.72d phg 0.5 Wachmann (1966) 2433680.364 -2106 +0.035 phg 1 Tschuprina (1952) 2434328.02 -1938 +1.65 phg 0 Fu (1964) 2434368.640 -1927 -0.032 phg 1 Shteiman (1958) 2434591.666 -1869 -0.044 phel 2 present paper^6 2434603.406 -1866 +0.159 phg 0.5 Wachmann (1966) 2434922.43 -1783 +0.01 vis 0.5 Marks (1959) 2435172.32 -1718 -0.06 vis 0.5 Marks^7 (1959) 2435303.355 -1684 +0.229 phg 0 Wachmann (1966) 2435338.146 -1675 +0.410 phg 0 Tschuprina (1957) 2435356.949 -1670 -0.014 phel 2 Walraven et al. (1958) 2435380.180 -1664 +0.144 vis 0.5 Azarnova (1957) 2435645.305 -1595 -0.070 phg 1 Shteiman (1958) 2435922.056 -1523 -0.194 vis 0.5 Azarnova (1958) 2436087.339 -1480 -0.268 vis 0 Vinnik^8 (1958) 2436099.119 -1477 +0.024 phel 2 Svolopoulos (1960) 2436214.589 -1447 +0.081 vis 0.5 Latyshev (1969) 2436448.952 -1386 -0.131 vis 0.5 Azarnova (1958) 2436903.132 -1268 +0.281 phg 0 Wachmann (1966) 2436926.058 -1262 +0.134 vis 0.5 Azarnova (1962) 2437198.867 -1191 -0.087 vis 0.5 Kiperman (1963) 2437287.383 -1168 -0.017 phel 3 Mitchell et al. (1964) 2437494.980 -1114 -0.077 vis 0.5 Kiperman (1963) 2437941.117 -998 -0.017 phel 2 Williams (1966) 2438179.565 -936 +0.011 vis 0.5 Ross, Hartmann (1972) 2438971.724 -730 0.000 vis 0.5 Borisov^9 (1972) 2438987.18 -726 +0.07 vis 0.5 Braune, Hubscher (1967) 2438994.833 2438994.418 -724 +0.034 -0.033d vis 1 Borisov (1972) 2439014.054 -719 +0.028 phel 3 Wisniewski, Johnson (1968) 2439344.655 -633 -0.083 vis 1 Borisov (1972) 2439740.868 -530 +0.044 vis 1 Borisov (1972) 2440482.991 -337 -0.013 vis 1 Borisov (1972) 2441778.985 2441778.619 0 +0.050 +0.030 phel 3 present paper Remarks: 1 Observer: Hartwig ; 2 Obs.: Flanery; 3 Obs.: Rybka; 4 Obs.: Model; 5 Obs.: Mielke; 6 Obs.: Detre; 7 Obs.: Wroblewski; 8 Obs.: Sazanova; 9 Obs.: Pantschuk. Figure 44 O-C diagram of SU Cyg shows the jump of the period as well, but the variations in the O-C values are not equal. The difference in the O-C values is equal to 0.15d in the case of the maximum, whereas it is equal to 0.23d for the median brightness. This means that the light curve has become steeper after the rejump. The time difference between the moments of a maximum and the preceding moment of median brightness on the ascending branch is nearly 0.35m . Considering that the median point has moved nearer the maximum, the increase in the steepness is about 20%. Y Aurigae Figure 45 V and B-V curves of Y Aur Table 28. O-C residuals for Y Aur Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2415474.705 -6799 +0.95d vis 1 Williams (1905b) 2415737.096 -6731 +0.040 vis 1 Williams (1905b) 2416215.714 -6607 +0.080 phg 1 Kukarkin (1931c) 2416254.236 -6597 +0.007 vis 1 Williams (1905b) 2416466.565 -6542 +0.063 vis 0.5 Lau (1904) 2417277.43 -6332 +0.43 vis 0 Luizet (1917) 2417639.779 2417639.505 -6238 -0.012 +0.68d vis 1 Zeipel (1908) 2417663.23 -6232 +0.28 vis 0 Luizet (1917) 2417944.675 2417944.320 -6159 -0.016 -0.017 vis 1 Van der Bilt (1924) 2418446.412 2418446.045 -6029 -0.014 -0.027 vis 1 Van der Bilt (1924) 2418755.56 -5949 +0.37 vis 0 Luizet (1917) 2419133.69 -5851 +0.27 vis 0 Luizet (1917) 2419322.538 2419322.187 -5802 +0.005 +0.008 vis 1 Van der Bilt (1924) 2419488.74 -5759 +0.25 vis 0 Luizet (1917) 2419805.36 -5677 +0.39 vis 0 Luizet (1917) 2419866.903 -5661 +0.180 phg 0.5 Robinson (1929) 2420600.12 -5471 +0.09 vis 0.5 Luizet (1917) 2420982.11 -5372 -0.01 vis 0.5 Luizet (1917) 2421140.394 -5331 +0.035 vis 1 Doberck (1924c) 2421167.333 2421166.924 -5324 -0.042 -0.097 phg 2 Jordan (1929) Table 28 (cont.) Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2422163.161 2422162.756 -5066 +0.34d -0.17d vis 1 Nijland (1923) 2422170.849 2422170.525 -5064 +0.003 +0.033 phg 2 Martin, Plummer (1921) 2422564.478 -4962 -0.037 vis 1 Doberck (1924c) 2422676.465 2422676.102 -4933 +0.024 +0.015 vis 1 Nijland (1923) 2422761.3 -4911 -0.05 vis 0.5 Hacar (1921) 2423043.097 2423042.773 -4838 +0.004 +0.034 vis 1 Nijland (1923) 2423355.680 -4757 -0.033 vis 1 Nijland (1923) 2423502.536 -4719 +0.162 phg 1 Kukarkin (1931c) 2423594.853 -4695 -0.149 vis 1 Doberck (1924c) 2425972.82 -4079 +0.36 vis 0 Kukarkin (1930a) 2426165.401 2426165.034 -4029 -0.029 -0.042 phg 1 Kukarkin (1931c) 2426234.922 -4011 +0.021 vis 1 Kukarkin (1940) 2428150.02 -3515 +0.81 vis 0 Fu (1964) 2430244.803 -2972 -0.121 vis 0.5 Lagrula (1941,1942) 2430785.41 -2832 +0.16 vis 0.5 Stein (1944) 2436833.102 -1265 +0.008 phel 3 Weaver et al. (1960) 2436844.654 -1262 -0.018 phel 2 Oosterhoff (1960) 2439361.069 2439360.687 -610 +0.001 -0.027 phel 3 Takase (1969) 2441715.370 2441715.027 0 +0.006 +0.017 phel 3 present paper Figure 46 O-C diagram of Y Aur The light and colour curves of this variable are shown in Fig. 45. The O-C residuals have been computed with the formulae: C_{max} = 2441715.364 + 3.859502d*E ; C_{med} = 2441715.010 + 3.859502d*E . Both O-C diagrams (Fig. 46) show constant period and give the same value for the period. ST Tauri According to Michalowska-Smak and Smak (1965) this star is a Population II variable. This statement can be refuted with the aid of the light and colour curves shown in Fig. 47. These Figure 47 V, B-V and U-B curves of ST Tau curves are typical of the classical cepheids. The O-C residuals have been computed with the formula: C = 2441761.963 + 4.034299d*E . The 2nd Supplement to the GCVS (Kukarkin et al. 1974) reports on the period variation of ST Tau. The O-C diagram (Fig. 48) does not show any period variation. Figure 48 O-C diagram of ST Tau Table 29 O-C residuals for ST Tau Obs.Max.J.D. E O-C Type w Source 2419718.565 -5464 +0.012d phg 0.5 Robinson (1930) 2420480.73 -5275 -0.31 vis 0.5 Hoffmeister (1919) 2420864.45 -5180 +0.16 vis 0.5 Hoffmeister (1919) 2421199.35 -5097 +0.21 vis 0.5 Hoffmeister (1919) 2423559.172 -4512 -0.034 vis 0.5 Doberck (1924c) 2424132.283 -4370 +0.207 phg 0.5 Kukarkina (1954b) 2428856.195 -3199 -0.045 phg 1 Koshkina (1963) 2429251.566 -3101 -0.036 phg 1 Koshkina (1963) 2430421.585 -2811 +0.036 vis 0.5 Model, Lochel (1964) 2433185.016 -2126 -0.027 phg 1 Borzdyko (1962) 2433806.267 -1972 -0.058 phg 0.5 Koshkina (1963) 2434024.192 -1918 +0.014 phg 0.5 Borzdyko (1962) 2434298.499 -1850 -0.011 phg 1 Koshkina (1963) 2435177.981 -1632 -0.006 phel 2 Walraven et al. (1958) 2435182.080 -1631 +0.059 phel 2 Irwin (1961) 2435323.165 -1596 -0.057 phg 1 Borzdyko (1962) 2436243.010 -1368 -0.032 phg 1 Borzdyko (1962) 2436993.473 -1182 +0.051 vis 0.5 Huth (1963b) 2437106.343 -1154 -0.039 phg 1 Borzdyko (1962) 2437622.781 -1026 +0.009 phel 3 Mitchell et al. (1964) 2437699.435 -1007 +0.011 phel 2 Michalowska et al. (1965) 2437989.839 -935 -0.054 phel 1 Williams (1966) 2441761.984 0 +0.021 phel 3 present paper V 395 Cassiopeiae This star has not previously been observed photoelectrically. The light and colour curves of V 395 Cas are presented in Fig. 49. Since the O-C diagram consists of two points only, these have not been plotted in a figure. The O-C residuals have been calculated with the formula: C = 2441949.427 + 4.37728d*E . Figure 49 V and B-V curves of V 395 Cas Table 30 O-C residuals for V 395 Cas Obs.Max.J.D. E O-C Type w Source 2435343.705 -1636 +0.001d phg 2 Kholopov et al. (1968) 2441949.427 0 0.000 phel 3 present paper SY Cassiopeiae Figure 50 V and B-V curves of SY Cas There is a faint companion SW at the variable within the diaphragm. The light and colour curves on SY Cas are presented in Fig. 50. The O-C residuals have been computed with the formula: C = 2441682.230 + 4.071098d*E . Figure 51 O-C diagram of SY Cas The O-C diagram (Fig. 51) shows a sudden period change at J.D. 2434000. The corresponding periods are as follows: before J.D. 2434000, P = 4.070969d ; after J.D. 2434000, P = 4.071098d . Table 31 O-C residuals for SY Cas Obs.Max.J.D. E O-C Type w Source 2414605.8 -6651 +0.4d phg 0.5 Blazhko (1907b) 2416376.8 -6216 +0.5 phg 0.5 Blazhko (1907b) 2417121.9 -6033 +0.6 phg 0.5 Blazhko (1907b) 2417793.55 -5868 +0.52 phg 0.5 Blazhko (1907b) 2417911.2 -5839 +0.1 phg 0 Blazhko (1907b) 2417952.374 -5829 +0.574 vis 0.5 Luizet (1908) 2418229.18 -5761 +0.55 vis 0.5 Luizet (1913) 2418595.42 -5671 +0.39 vis 0.5 Luizet (1913) 2419047.38 -5560 +0.45 vis 0.5 Luizet (1913) 2419234.76 -5514 +0.56 vis 0.5 Luizet (1913) 2419336.475 -5489 +0.502 phg 1 Robinson (1931a) 2419466.81 -5457 +0.56 vis 0.5 Luizet (1913) 2419743.57 -5389 +0.49 vis 0.5 Luizet (1913) 2421131.676 -5048 +0.349 phg 2 Jordan (1929) 2425964.01 -3861 +0.29 phg 1 Oosterhoff (1935) 2426851.52 -3643 +0.30 phg 1 Oosterhoff (1935) 2427335.74 -3524 +0.06 phg 0.5 Oosterhoff (1935) 2428431.13 -3255 +0.32 phg 0.5 Fu (1964) 2430181.504 -2825 +0.126 vis 1 Conceicao-Silva (1950b) 2430433.905 -2763 +0.119 phg 1 Vasil'yanovskaya (1948) 2430629.53 -2715 +0.33 phg 0 Romano (1959) 2430678.192 -2703 +0.140 vis 0.5 Conceicao-Silva (1950b) 2430836.932 -2664 +0.107 phg 1 Solov'yov (1954) 2430979.55 -2629 +0.24 phg 0.5 Romano (1959) 2431146.305 -2588 +0.077 phg 2 Vasil'yanovskaya (1948) 2431687.72 -2455 +0.04 phg 0.5 Romano (1959) 2432041.82 -2368 -0.05 phg 0.5 Romano (1959) 2432127.439 -2347 +0.076 vis 0.5 Conceicao-Silva (1950b) 2432208.850 -2327 +0.065 phg 1 Vasil'yanovskaya (1948) 2432738.37 -2197 +0.34 phg 0 Romano (1959) 2432970.172 -2140 +0.092 phg 1 Solov'yov (1954) 2433121.25 -2103 +0.54 phg 0 Romano (1959) Table 31 (cont.) Obs.Max.J.D. E O-C Type w Source 2435083.29 -1621 +0.31d phg 0 Romano (1959) 2435413.05 -1540 +0.31 phg 0 Romano (1959) 2435721.87 -1464 -0.27 phg 0 Romano (1959) 2436809.135 -1197 -0.009 phel 3 Oosterhoff (1960) 2436833.544 -1191 +0.008 phel 3 Weaver et al. (1960) 2436906.850 -1173 +0.018 phel 3 Bahner et al. (1962) 2437045.355 -1139 +0.106 vis 0.5 Haussler (1973) 2437399.402 -1052 -0.033 vis 0.5 Haussler (1973) 2438144.399 -869 -0.047 vis 0.5 Haussler (1973) 2439056.378 -645 +0.006 vis 0.5 Haussler (1973) 2440151.424 -376 -0.073 vis 0.5 Haussler (1973) 2441682.236 0 +0.006 phel 3 present paper 2443041.968 +334 -0.009 phel 2 present paper V 508 Monocerotis This star has not previously been observed photoelectrically. The amplitude of its light variation is small (see Fig. 52) but non-sinusoidal (resembling IR Cep). As was discussed in the case of IR Cep, this phenomenon may be due to the presence of a companion star or to the non-homogeneity of the group of cepheids with small amplitude. As the ratio of amplitudes in yellow and blue lights for both IR Cep and V 508 Mon is close to the value of the ratio derived for single cepheids (i.e. the possible companion star would be of the same spectral type as the cepheid in both cases), the latter explanation is more probable. Figure 52 V and B-V curves of V 508 Mon The O-C residuals have been computed with the formula: C = 2441732.070 + 4.133608d*E . As Fig. 53 shows, the period of V 508 Mon has remained constant since the discovery of its light variation. Figure 53 O-C diagram of V 508 Mon Table 32 O-C residuals for V 508 Mon Obs.Max.J.D. E O-C Type w Source 2429343.80 -2997 +0.15d phg 0.5 Wachmann (1964) 2429670.23 -2918 +0.03 phg 0.5 Wachmann (1964) 2430021.53 -2833 -0.03 phg 0.5 Wachmann (1964) 2430699.44 -2669 -0.03 phg 0.5 Wachmann (1964) 2431116.93 -2568 -0.03 phg 0.5 Wachmann (1964) 2431852.67 -2390 -0.08 phg 0.5 Wachmann (1964) 2432233.03 -2298 -0.01 phg 0.5 Wachmann (1964) 2432948.14 -2125 -0.01 phg 0.5 Wachmann (1964) 2433332.53 -2032 -0.05 phg 0.5 Wachmann (1964) 2434068.40 -1854 +0.04 phg 0.5 Wachmann (1964) 2434444.56 -1763 +0.04 phg 0.5 Wachmann (1964) 2434775.15 -1683 -0.06 phg 0.5 Wachmann (1964) 2435163.80 -1589 +0.03 phg 0.5 Wachmann (1964) 2435453.15 -1519 +0.03 phg 0.5 Wachmann (1964) 2437693.63 -977 +0.10 phg 0.5 Wachmann (1964) 2441732.043 0 -0.027 phel 3 present paper SX Persei Figure 54 V and B-V curves of SX Per The light and colour curves for this variable are shown in Fig. 54. The O-C residuals are computed with the formula: C = 2441847.979 + 4.1289967d*E . As Fig. 55 shows, the period of SX Per has remained constant since the beginning of this century. Figure 55 O-C diagram of SX Per Table 33 O-C residuals for SX Per Obs.Max.J.D. E O-C Type w Source 2418210.070 -5510 -0.191d phg 0.5 Kukarkin (1931b) 2418390.436 -5468 -0.003 vis 0.5 Enebo (1911) 2418647.85 -5408 +0.01 phg 0.5 Oosterhoff (1935) 2419810.411 -5137 -0.008 vis 0.5 Nijland (1923) 2420127.795 -5063 -0.081 vis 0.5 Nijland (1923) 2420475.343 -4982 -0.020 vis 0.5 Nijland (1923) 2420857.163 -4893 -0.007 vis 1 Nijland (1923) 2421161.80 -4822 +0.04 phg 0.5 Oosterhoff (1935) 2421187.512 -4816 +0.014 vis 1 Nijland (1923) 2421638.07 -4711 +0.13 phg 0.5 Oosterhoff (1935) 2425692.20 -3766 +0.24 phg 0.5 Oosterhoff (1935) 2425966.69 -3702 +0.17 phg 0.5 Oosterhoff (1935) 2427064.69 -3446 -0.06 phg 0.5 Oosterhoff (1935) 2429145.60 -2961 +0.21 phg 0.5 Kurochkin (1950) 2436815.866 -1173 +0.018 phel 3 Weaver et al. (1960) 2436845.854 -1166 -0.023 phel 2 Oosterhoff (1960) 2441847.956 0 -0.023 phel 3 present paper Y Lacertae Table 34 O-C residuals for Y Lac Obs.Max.J.D. E O-C Type w Source 2417615.86 -5581 +0.11d phg 0.5 Blazhko (1907a) 2417715.193 -5558 -0.005 vis 0.5 Ichinohe (1909) 2417944.323 -5505 -0.035 vis 0.5 Zeipel (1908) 2418216.813 -5442 +0.057 vis 0.5 Ichinohe (1909) 2418424.295 -5394 -0.002 phg 0.5 Robinson (1930) 2421658.488 -4646 +0.006 phg 2 Jordan (1929) 2421818.386 -4609 -0.075 phg 2 Martin, Plummer (1919) 2424758.640 -3929 +0.011 vis 0.5 Schneller (1928) 2426228.749 -3589 +0.036 phg 0.5 Nekrasova (1938) 2429102.45 -2924 -1.57 phg 0 Shakhovskoj (1949) 2433125.147 -1994 +0.011 phel 3 Eggen (1951) 2433609.468 -1882 +0.069 phg 1 Solov'yov (1952b) Table 34 (cont.) Obs.Max.J.D. E O-C Type w Source 2436834.936 -1136 +01001 phel 3 Bahner et al. (1962) 2437366.745 -1013 -0.015 phel 3 Mitchell et al. (1964) 2441746.720 0 -0.025 phel 3 present paper The light and colour curves for this variable are shown in Fig. 56. According to Madore (1977), Y Lac has a blue photometric companion. The O-C residuals have been calculated with the formula: C = 2441746.745 + 4.323776d*E . Figure 56 V, B-V and U-B curves of Y Lac Figure 57 O-C diagram of Y Lac The O-C diagram (Fig. 57) is a straight line, i.e. the period is constant. V 402 Cygni The light and colour curves of this variable are shown in Fig. 58. The O-C residuals have been computed with the formula: C = 2441698.635 + 4.364836d*E . These residuals which are plotted in Fig. 59 show constant period. Figure 58 V and B-V curves of V 402 Cyg Figure 59 O-C diagram of V 402 Cyg Table 35 O-C residuals for V 402 Cyg Obs.Max.J.D. E O-C Type w Source 2413841.80 -6382 -0145 phg 0 Ikauniex (1946) 2414606.10 -6207 0.00 phg 0.5 Ikauniex (1946) 2415287.05 -6051 +0.04 phg 0.5 Ikauniex (1946) 2417613.45 -5518 -0.02 phg 0.5 Ikauniex (1946) 2418586.80 -5295 -0.03 phg 0.5 Ikauniex (1946) 2428717.71 -2974 +0.10 phg 0.5 Ikauniex (1946) 2428748.30 -2967 +0.13 phg 0.5 Suzuki, Huruhata (1938) 2430166.83 -2642 +0.09 phg 0.5 Ashbrook (1941) 2430446.124 -2578 +0.036 phg 0.5 Solov'yov (1946) 2430651.211 -2531 -0.024 phg 0.5 Filatov (1957) 2430956.765 -2461 -0.009 phg 1 Solov'yov (1946) 2430961.19 -2460 +0.05 phg 0.5 Ikauniex (1946) 2431410.654 -2357 -0.063 phg 0.5 Solov'yov (1946) 2431655.134 -2301 -0.013 phg 0.5 Filatov (1957) Table 35 (cont.) Obs.Max.J.D. E O-C Type w Source 2432794.380 -2040 +0.010d phg 0.5 Filatov (1957) 2433121.697 -1965 -0.035 phg 0.5 Filatov (1957) 2433649.937 -1844 +0.060 phg 1 Filatov (1957) 2433890.004 -1789 +0.061 phg 0.5 Shteiman (1958) 2434400.571 -1672 -0.058 phg 1 Filatov (1957) 2434448.650 -1661 +0.008 phg 0.5 Shteiman (1958) 2435334.826 -1458 +0.122 phg 0.5 Filatov (1957) 2435692.675 -1376 +0.054 phg 1 Shteiman (1958) 2436761.948 -1131 -0.057 phel 3 Oosterhoff (1960) 2437307.560 -1006 -0.050 phel 3 Mitchell et al. (1964) 2439743.193 -448 +0.005 phel 3 Takase (1969) 2441698.620 0 -0.015 phel 3 present paper T Vulpeculae The light and colour curves for this cepheid are shown in Fig. 60. The O-C residuals have been calculated with the formula: C = 2441705.121 + 4.435462d*E . Figure 60 V, B-V and U-B curves of T Vul The O-C diagram in Fig. 61 shows a small change in the period of T Vul at J.D. 2434000. The value of the period before J.D. 2417000 is rather uncertain. The other values of the period are as follows: between J.D. 2417000 and J.D. 2434000, P = 4.435589d ; after J.D. 2434000. P = 4.435462d . Figure 61 O-C diagram of T Vul Table 36 O-C residuals for T Vul Obs.Max.J.D. E O-C Type w Source 2409884.531 -7174 -0.586d vis 0.5 Sawyer (1889) 2409897.709 -7171 -0.714 vis 0.5 Chandler (1886) 2410101.830 -7125 -0.624 vis 0.5 Chandler (1886) 2410199.373 -7103 -0.661 vis 0.5 Sawyer (1889) 2410212.91 -7100 -0.43 vis 0.5 Prager^1 (1936) 2410545.403 -7025 -0.557 vis 0.5 Sawyer (1896) 2410904.747 -6944 -0.526 vis 0.5 Sawyer (1896) 2410922.543 -6940 -0.472 vis 0.5 Yendell (1889) 2411272.927 -6861 -0.489 vis 0.5 Sawyer (1896) 2411313.392 -6852 +0.057 vis 0 Yendell (1890) 2411605.959 -6786 -0.117 vis 0.5 Yendell (1891) 2411991.774 -6699 -0.187 vis 0.5 Yendell (1893) 2412351.012 -6618 -0.221 vis 0.5 Yendell (1894) 2412404.048 -6606 -0.411 vis 0.5 Sawyer (1896) 2412670.178 -6546 -0.409 vis 0.5 Yendell (1895a) 2412736.725 -6531 -0.394 vis 0.5 Sawyer (1896) 2413056.175 -6459 -0.297 vis 0.5 Yendell (1895b) 2413096.011 -6450 -0.380 vis 0.5 Sawyer (1896) 2413761.565 -6300 -0.145 vis 0.5 Yendell (1897) 2414098.541 -6224 -0.265 vis 0.5 Yendell (1901) 2414213.467 -6198 -0.661 vis 0.5 Pickering (1907) 2414546.374 -6123 -0.413 vis 0.5 Luizet (1912) 2414870.265 -6050 -0.311 vis 0.5 Yendell (1901) 2414892.283 -6045 -0.470 vis 0.5 Luizet (1912) 2415211.636 -5973 -0.470 vis 0.5 Luizet (1912) 2415570.948 -5892 -0.431 vis 0.5 Luizet (1912) 2415801.604 -5840 -0.419 vis 0.5 Tass (1909) 2415925.05 -5812 -1.17 vis 0 Yendell (1905) 2415987.800 -5798 -0.512 vis 0.5 Luizet (1912) 2416120.895 -5768 -0.481 vis 0.5 Tass (1904) 2416324.921 -5722 -0.488 vis 0.5 Luizet (1912) 2416710.960 -5635 -0.333 vis 0.5 Terkan (1905) 2416715.297 -5634 -0.431 vis 0.5 Luizet (1912) 2417065.499 -5555 -0.631 vis 0.5 Luizet (1912) 2417069.989 -5554 -0.576 phg 0.5 Wilkens (1906) 2417433.887 -5472 -0.386 vis 0.5 Luizet (1912) 2417757.672 -5399 -0.390 vis 0.5 Zeipel (1908) 2417806.307 -5388 -0.545 vis 0.5 Luizet (1912) 2417872.917 -5373 -0.467 vis 1 Nijland (1923) 2418192.402 -5301 -0.335 vis 0.5 Luizet (1912) Table 36 (cont.) Obs.Max.J.D. E O-C Type w Source 2418196.696 -5300 -0.476d vis 1 Nijland (1923) 2418516.031 -5228 -0.495 vis 1 Nijland (1923) 2418551.555 -5220 -0.454 vis 0.5 Luizet (1912) 2418937.503 -5133 -0.392 vis 0.5 Luizet (1912) 2419283.487 -5055 -0.374 vis 0.5 Luizet (1912) 2419656.159 -4971 -0.280 phg 0.5 Robinson (1931a) 2419833.616 -4931 -0.242 vis 0.5 Dziewulski (1925) 2420001.954 -4893 -0.451 phg 1 Hertzsprung (1919) 2420747.163 -4725 -0.400 phg 1 Hertzsprung (1919) 2420813.763 -4710 -0.332 vis 0.5 Luyten (1922) 2421110.716 -4643 -0.555 vis 0.5 Luyten (1922) 2421439.068 -4569 -0.427 vis 0.5 Luyten (1922) 2421922.671 -4460 -0.289 vis 0.5 Luyten (1922) 2422641.203 -4298 -0.302 vis 0.5 Doberck (1924a) 2423333.034 -4149 -0.355 vis 0.5 Hellerich (1928b) 2423670.279 -4066 -0.254 vis 0.5 Hellerich (1928b) 2423674.582 -4065 -0.386 vis 0.5 Hopmann (1924) 2424029.526 -3985 -0.279 vis 0.5 Hellerich (1928b) 2424375.465 -3907 -0.306 phel 3 Huffer (1928a) 2424384.452 -3905 -0.190 vis 0.5 Hellerich (1928b) 2424721.445 -3829 -0.292 phel 3 Huffer (1928a) 2424770.258 -3818 -0.269 vis 0.5 Kukarkin (1940) 2425067.340 -3751 -0.363 vis 0.5 Kukarkin (1940) 2425116.349 -3740 -0.144 phg 2 Hellerich (1935) 2425218.28 -3717 -0.23 vis 0.5 Lause (1938) 2425426.662 -3670 -0.313 vis 0.5 Kukarkin (1940) 2425448.942 -3665 -0.211 vis 1 Zverev (1936) 2425701.800 -3608 -0.174 vis 0.5 Dziewulski et al. (1932) 2425781.623 -3590 -0.189 vis 1 Zverev (1936) 2425826.001 -3580 -0.166 vis 0.5 Kukarkin (1940) 2426531.289 -3421 -0.116 vis 0.5 Kukarkin (1940) 2426540.081 -3419 -0.195 vis 1 Zverev (1936) 2426859.380 -3347 -0.250 phg 2 Kox (1935) 2427289.6 -3250 -0.3 vis 0.5 Miczaika (1934) 2427875.176 -3118 -0.174 vis 0.5 Miczaika (1937) 2428451.646 -2988 -0.315 vis 1 Kepinski (1937) 2429631.665 -2722 -0.128 vis 0.5 Mandre (1950,1951) 2430004.44 -2638 +0.07 vis 0.5 Conceicao-Silva (1948) 2432967.224 -1970 -0.037 phel 3 Eggen (1951) 2434595.171 -1603 +0.096 phel 1 present paper 2434701.51 -1579 -0.02 vis 0.5 MarkS^3 (1959) 2435216.19 -1463 +0.15 vis 0.5 Marks (1959) 2435362.383 -1430 -0.027 phel 1 Walraven et al. (1958) 2435380.378 -1426 +0.226 vis 0.5 Azarnova (1957) 2435757.163 -1341 -0.003 phel 3 Prokof'eva (1961) 2436098.622 -1264 -0.075 phel 2 Svolopoulos (1960) 2436214.045 -1238 +0.026 vis 0.5 Latyshev (1969) 2437212.010 -1013 +0.012 phel 2 Mitchell et al. (1964) 2437562.372 -934 -0.027 phel 3 Johansen (1971) 2437939.516 -849 +0.102 phel 1 Williams (1966) 2438649.080 -689 -0.008 phel 3 Johansen (1971) 2438733.347 -670 -0.014 phel 2 Wisniewski et al. (1968) 2441705.118 0 -0.003 phel 3 present paper Remarks: 1 Observer: Gore; 2 Obs.: Detre; 3 Obs.: Wroblewski. FF Aquilae This cepheid is a component of a spectroscopic binary system with an orbital period of 1435 days (Abt 1959). Its light and colour curves are presented in Fig. 62. The small bump before the minimum brightness seems to be real because it appears in all three colours and its presence can be suspected from some earlier photoelectric light curves, as well. The appearance of a bump at this phase is a unique phenomenon among the cepheids with such a short period. Figure 62 V, B-V and U-B curves of FF Aql Figure 63 O-C diagram of FF Aql The O-C residuals have been computed with the formulae; C_{max} = 2441576.428 + 4.470916d*E ; C_{med} = 2441575.542 + 4.470916d*E . These residuals are shown in Fig. 63 . It can be seen from this figure that either the period determined from the O-C diagram of the median brightness (P = 4.470886d) differs from the period valid Table 37 O-C residuals for FF Aql Obs.Max.J.D. Obs.Med.J.D. E O-C O-C Type w Source max med 2424703.102 -3774 -0.089d vis 1 Kukarkin (1931b) 2425096.650 2425095.823 -3686 +0.018 +0.077d phel 3 Huffer (1931) 2425490.067 2425489.334 -3598 -0.005 +0.148 phel 3 Huffer (1931) 2425735.99 -3543 +0.02 vis 1 Kukarkin (1929) 2425803.008 -3528 -0.028 vis 1 Kukarkin (1940) 2425811.968 2425811.248 -3526 -0.010 +0.156 phel 3 Huffer (1931) 2425973.030 -3490 +0.099 vis 0.5 Zverev (1936) 2426433.462 -3387 +0.026 vis 1 Kukarkin (1940) 2426495.904 -3373 -0.124 vis 1 Selivanov (1935) 2426504.899 -3371 -0.071 vis 1 Loreta (1933) 2426540.654 -3363 -0.083 vis 1 Zverev (1936) 2426594.117 -3351 -0.271 vis 0 Dufay (1947b) 2426867.069 -3290 -0.045 vis 1 Loreta (1933) 2427068.35 -3245 +0.04 vis 1 Selivanov (1934) 2427202.382 -3215 -0.051 vis 1 Selivanov (1935) 2427627.007 -3120 -0.163 vis 1 Selivanov (1935) 2427658.447 -3113 -0.019 vis 1 Krebs (1935) 2430703.186 -2432 +0.026 vis 1 Dziewulski (1962) 2432960.946 2432960.088 -1927 -0.027 +0.001 phel 3 Eggen (1951) 2434611.17 -1558 +0.43 vis 0 Marks^1 (1959) 2434628.641 2434627.796 -1554 +0.016 +0.057 phel 3 present paper^2 2435625.598 2435624.685 -1331 -0.041 -0.068 phel 3 Walraven et al. (1958) 2436099.567 -1225 +0.011 phel 2 Svolopoulos (1960) 2437199.443 -979 +0.042 vis 1 Makarenko^3 (1968) 2437320.127 2437319.215 -952 +0.011 -0.015 phel 3 Mitchell et al. (1964) 2437494.473 -913 -0.009 vis 1 Makarenko^3 (1968) 2437878.791 -827 -0.189 phel 1 Williams (1966) 2439019.100 2439018.170 -572 +0.036 -0.008 phel 3 Wisniewski, Johnson (1968) 2440811.901 2440810.980 -171 0.000 -0.035 phel 3 Pel (1976) 2441576.448 2441575.590 0 +0.020 +0.048 phel 3 present paper Remarks: 1 Observer: Wroblewski; 2 Observer: Detre; 3 Observer: Kiperman for the maximum brightness or a phase jump took place at the median brightness. This phenomenon has already been discussed in the case of SU Cygni. A worthy subject for further investigations would be to determine whether there is some kind of connection between the mentioned peculiarities (variable steepness of the rising branch, bump on the light curve) and the presence of a magnetic field at this star (Babcock 1958). The points in the O-C diagrams in Fig. 63 derived from photoelectric observations show larger scatter than expected. This scatter is a result of the orbital motion of FF Aql around the centre of mass of the binary system. Let us examine the deviations of the O-C residuals (derived from photoelectric observations) from the expected value of O-C (solid line at the upper O-C diagram in Fig. 63). These deviations and the related orbital phases are listed in Table 38. The orbital phases are computed with the formula: Epoch + phase = (J.D. - 2420000) * 0.0006969 . Table 38 Max. Obs. \Delta(O-C) Phase Max. Obs. \delta(O-C) Phase 2425096.650 +0.018d .55 2435625.598 -0.041d .89 2425490.081 -0.005 .83 2437320.127 +0.011 .07 2425811.968 -0.010 .05 2439019.100 +0.036 .25 2432960.946 -0.027 .03 2440811.901 0.000 .50 2434628.641 +0.016 .19 2441576.448 +0.020 .04 Figure 64 O-C variations due to the orbital motion The data derived from the curve of O-C variations versus the orbital phase (Fig. 64) are in good agreement with those derived by Abt (1959). The value of a*\sin i can be determined from the amplitude of the O-C variation curve. The result is: a*\sin i = 78.10^6 km (˜15.10^6 km). Abt obtained 68.3*10^6 km for this value from spectroscopic observations. Thus the spectroscopically and optically determined values of a*\sin i are very similar. Moreover, the moment of the point with largest positive deviation of O-C must coincide with the moment when the cepheid is the furthest from the observer during its orbital motion (i.e. at 0.23d from periastron according to Abt). This coincidence is very good, but the time of the nearest point does not coincide so well with the largest negative deviation of O-C. On the basis of the data given in Table 38 I suggest a slightly smaller value for the orbital period. The deviations of O-C plotted with a period of 1400d results in a curve with smaller scatter. Moreover, the curve constructed from Abt's data on the mean velocity with the period of 1400 days shows less scatter than in the case of larger period (only two points with very low weight deviate considerably). Thus the suggested new value of the orbital period is P_{orb} = 1400d ˜ 15d. XY Cassiopeiae The light and colour curves for this variable are shown in Fig. 65. The O-C residuals have been computed with the formula: C = 2442006.786 + 4.501697d*E . Figure 65 V and B-V curves of XY Cas Figure 66 shows that the period has remained constant since the discovery of the light variation of XY Cas. The period change reported by Solov'yov (1954) cannot be confirmed. Figure 66 O-C diagram of XY Cas Table 39 O-C residuals for XY Cas Obs.Max.J.D. E O-C Type w Source 2419403.784 -5021 +0.019d phg 0.5 Robinson (1929) 2422541.383 -4324 -0.065 phg 1 Lehmann-Balan. (1924) 2423919.026 -4018 +0.059 vis 0.5 Selivanov (1928) 2424859.820 -3809 -0.002 vis 0.5 Selivanov (1928) 2425845.76 -3590 +0.07 phg 0.5 Oosterhoff (1935) 2426287.00 -3492 -0.14 phg 0 Oosterhoff (1935) 2426705.737 -3399 +0.219 vis 0 Kukarkin (1940) 2426709.946 -3398 -0.074 vis 1 Dunst (1932) 2426714.49 -3397 -0.03 phg 0.5 Oosterhoff (1935) 2426948.71 -3345 +0.10 phg 0.5 Oosterhoff (1935) 2427335.74 -3259 -0.02 phg 0.5 Oosterhoff (1935) 2428466.03 -3008 +0.35 phg 0 Fu (1964) 2430761.585 -2498 +0.038 phg 1 Solov'yov (1954) 2433147.420 -1968 -0.026 phg 1 Solov'yov (1954) 2434340.403 -1703 +0.007 phg 1 Tsarevsky (1960) 2435456.868 -1455 +0.051 phg 1 Tsarevsky (1960) 2436136.605 -1304 +0.032 phg 1 Tsarevsky (1960) 2436474.306 -1229 +0.106 phg 1 Tsarevsky (1960) 2436820.826 -1152 -0.005 phel 3 Oosterhoff (1960) 2436829.852 -1150 +0.018 phel 3 Weaver et al. (1960) 2436901.796 -1134 -0.066 phel 3 Bahner et al. (1962) 2437365.373 -1031 -0.163 vis 0.5 Berthold (1973) 2439031.023 -661 -0.141 vis 0.5 Berthold (1973) 2439818.991 -486 +0.030 phel 3 present paper^1 2442006.751 0 -0.035 phel 3 present paper 2442097.08 +20 +0.26 vis 0 Small (1974) Remark: 1 Observer: Abaffy. VZ Cygni The light and colour curves of this variable are shown in Fig. 67. The O-C residuals have been computed with the formula: C = 2441705.702 + 4.864453d*E . The O-C diagram presented in Fig. 68 shows a period change: before J.D. 2434000, P = 4.864583d ; after J.D. 2434000, P = 4.864453d . Figure 67 V, B-V and U-B curves of VZ Cyg Figure 68 O-C diagram of VZ Cyg Table 40 O-C residuals for VZ Cyg Obs.Max.J.D. E O-C Type w Source 2416658.035 -5149 -0.599d vis 0.5 Graff (1914) 2416799.165 -5120 -0.538 vis 0.5 Zinner^1 (1932) 2417062.0 -5066 -0.4 vis 0.5 Seares (1907a) 2417066.4 -5065 -0.8 vis 0 Blazhko (1906) 2417207.798 -5036 -0.519 vis 0.5 Zinner^1 (1932) 2417485.2 -4979 -0.4 vis 0.5 Seares (1907a) 2417499.783 -4976 -0.401 vis 0.5 Zinner^1 (1932) 2417762.528 -4922 -0.336 vis 0.5 Zeipel (1908) 2417815.980 -4911 -0.393 vis 0.5 Zinner^1 (1932) 2417820.912 -4910 -0.326 vis 0.5 Luizet (1909) 2418195.396 -4833 -0.405 vis 0.5 Zinner^1 (1932) 2418224.569 -4827 -0.418 vis 0.5 Luizet (1909) 2418560.219 -4758 -0.416 vis 0.5 Zinner^1 (1932) 2419158.686 -4635 -0.276 vis 0.5 Zinner^1 (1932) Table 40 (cont.) Obs.Max.J.D. E O-C Type w Source 2419859.095 -4491 -0.349d vis 0.5 Zinner^1 (1932) 2420379.476 -4384 -0.464 vis 0.5 Zinner^1 (1932) 2420627.598 -4333 -0.405 vis 1 Doberck (1920a) 2420642.129 -4330 -0.493 phg 0.5 Robinson (1930) 2420768.758 -4304 -0.338 vis 0.5 Zinner^1 (1932) 2421084.891 -4239 -0.395 vis 0.5 Zinner^1 (1932) 2421114.079 -4233 -0.393 phg 2 Jordan (1929) 2421386.567 -4177 -0.315 vis 0.5 Zinner^1 (1932) 2421498.432 -4154 -0.332 vis 1 Doberck (1920a) 2421722.207 -4108 -0.322 vis 0.5 Zinner^1 (1932) 2422165.164 -4017 -0.030 vis 0 Zinner^1 (1932) 2422179.388 -4014 -0.400 vis 1 Doberck (1920a) 2422588.133 -3930 -0.269 vis 0.5 Zinner^1 (1932) 2422656.134 -3916 -0.370 phg 1 Jordan (1929) 2423040.508 -3837 -0.288 vis 0.5 Zinner^1 (1932) 2423327.580 -3778 -0.219 vis 0.5 Doberck (1924b) 2423507.509 -3741 -0.274 vis 1 Nielsen (1954) 2423692.305 -3703 -0.328 vis 0.5 Doberck (1924b) 2424996.109 -3435 -0.197 phg 1 Wachmann (1935) 2426163.550 -3195 -0.225 phg 1 Wachmann (1935) 2426513.862 -3123 -0.153 phg 1 Wachmann (1935) 2426898.035 -3044 -0.272 phg 1 Wachmann (1935) 2427029.614 -3017 -0.033 vis 0.5 Dziewulski et al. (1938) 2427321.296 -2957 -0.218 phg 2 Gesundheit (1938) 2427360.339 -2949 -0.091 vis 0.5 Dziewulski et al. (1938) 2427739.687 -2871 -0.170 phg 2 Gesundheit (1938) 2428848.680 -2643 -0.273 phg 1 Abidov (1963) 2429096.894 -2592 -0.146 phg 1 Abidov (1963) 2429452.007 -2519 -0.138 phg 1 Abidov (1963) 2429812.004 -2445 -0.110 phg 1 Abidov (1963) 2429933.686 -2420 -0.040 vis 0.5 Conceicao-Silva (1950a) 2430269.317 -2351 -0.056 vis 0.5 Conceicao-Silva (1950a) 2430571.42 -2289 +0.45 vis 0 Stein (1944) 2430624.483 -2278 +0.005 vis 0.5 Conceicao-Silva (1950a) 2430921.153 -2217 -0.057 vis 0.5 Conceicao-Silva (1950a) 2432755.06 -1840 -0.05 phg 1 Novikov (1951) 2433387.402 -1710 -0.085 phg 1 Abidov (1963) 2433903.002 -1604 -0.117 phg 0.5 Abidov (1963) 2434219.193 -1539 -0.116 phg 1 Abidov (1963) 2434589.022 -1463 +0.015 phg 1 Abidov (1963) 2434953.849 -1388 +0.008 phg 0.5 Abidov (1963) 2435323.677 -1312 +0.137 phg 0.5 Abidov (1963) 2435362.501 -1304 +0.046 phg 1 Vyskupaitis (1961) 2436773.146 -1014 -0.001 phel 3 Weaver et al. (1960) 2436802.348 -1008 +0.015 phel 3 Oosterhoff (1960) 2437352.009 -895 -0.008 phel 3 Mitchell et al. (1964) 2437556.280 -853 -0.044 vis 0.5 Schreier (1962) 2441705.698 0 -0.004 phel 3 present paper 2443062.886 +279 +0.002 phel 2 present paper Remark: 1 Observer: Hartwig V 1154 Cygni The cepheid V 1154 Cygni has a faint companion about 20" S. The light and colour curves for this variable are shown in Fig. 69. Unfortunately, the U-B colour curve is not complete. The O-C residuals have been calculated with the formula: C = 2441494.442 + 4.925460d*E . According to Fig. 70 this star has a constant period. Figure 69 V, B-V and U-B curves of V 1154 Cyg Figure 70 O-C diagram of V 1154 Cyg Table 41 O-C residuals for V 1154 Cyg Obs.Max.J.D. E O-C Type w Source 2416044.647 -5167 +0.57d phg 0.5 Strohmeier et al. (1968) 2419265.632 -4513 -0.209 phg 0.5 Strohmeier et al. (1968) 2419349.471 -4496 -0.103 phg 0.5 Strohmeier et al. (1968) 2419595.739 -4446 -0.108 phg 0.5 Strohmeier et al. (1968) 2420009.616 -4362 +0.031 phg 0.5 Strohmeier et al. (1968) 2420423.492 -4278 +0.168 phg 0.5 Strohmeier et al. (1968) Table 41 (cont.) Obs.Max.J.D. E O-C Type w Source 2420852.283 -4191 +0.440d phg 0.5 Strohmeier et al. (1968) 2421846.916 -3989 +0.134 phg 0.5 Strohmeier et al. (1968) 2422230.609 -3911 -0.359 phg 0.5 Strohmeier et al. (1968) 2422895.733 -3776 -0.172 phg 0.5 Strohmeier et al. (1968) 2423984.587 -3555 +0.156 phg 0.5 Strohmeier et al. (1968) 2426427.558 -3059 +0.098 phg 0.5 Ott (1966) 2426531.072 -3038 +0.178 phg 0.5 Strohmeier et al. (1968) 2426846.198 -2974 +0.074 phg 0.5 Strohmeier et al. (1968) 2426880.322 -2967 -0.280 phg 0.5 Ott (1966) 2427260.218 -2890 +0.356 phg 0.5 Strohmeier et al. (1968) 2427303.838 -2881 -0.353 phg 0.5 Ott (1966) 2427530.835 -2835 +0.072 phg 0.5 Strohmeier et al. (1968) 2427919.762 -2756 -0.112 phg 0.5 Strohmeier et al. (1968) 2428067.411 -2726 -0.227 phg 0.5 Ott (1966) 2428777.082 -2582 +0.178 phg 0.5 Strohmeier et al. (1968) 2429077.290 -2521 -0.067 phg 0.5 Ott (1966) 2429456.525 -2444 -0.093 phg 0.5 Strohmeier et al. (1968) 2429825.703 -2369 -0.325 phg 0.5 Strohmeier et al. (1968) 2430535.260 -2225 -0.033 phg 0.5 Strohmeier et al. (1968) 2430673.244 -2197 +0.036 phg 0.5 Nikulina (1970) 2431717.643 -1985. +0.239 phg 0.5 Nikulina (1970) 2432776.449 -1770 +0.071 phg 0.5 Nikulina (1970) 2433406.659 -1642 -0.177 phg 0.5 Nikulina (1970) 2433790.836 -1564 -0.186 phg 0.5 Strohmeier et al. (1968) 2434248.806 -1471 -0.284 phg 0.5 Strohmeier et al. (1968) 2434480.757 -1424 +0.170 phg 0.5 Nikulina (1970) 2434983.354 -1322 +0.370 phg 0.5 Nikulina (1970) 2435445.884 -1228 -0.093 phg 0.5 Nikulina (1970) 2436495.184 -1015 +0.084 phg 0.5 Nikulina (1970) 2436780.793 -957 +0.013 phg 0.5 Ott^1 (1966) 2437199.479 -872 +0.038 phg 0.5 Ott^2 (1966) 2437332.550 -845 +0.122 phg 0.5 Nikulina (1970) 2437583.294 -794 -0.332 phg 0.5 Ott (1966) 2437706.869 -769 +0.106 phg 0.5 Busch, Haussler (1966) 2437918.353 -726 -0.205 phg 0.5 Ott (1966) 2438287.920 -651 -0.047 phg 0.5 Ott^2 (1966) 2438425.857 -623 -0.023 phg 0.5 Nikulina (1970) 2438662.447 -575 +0.145 phg 0.5 Ott^2 (1966) 2439031.788 -500 +0.076 phg 0.5 Ott^2 (1966) 2441006.788 -99 -0.033 phel 3 Wachmann (1976) 2441494.482 0 +0.040 phel 3 present paper Remarks: 1 Observer: Weber; 2 Obs.: Haussler. AS Persei The light and colour curves of this star based on the observations made between 1972-1974 are shown in Fig. 71. It is highly interesting that the amplitude of the light variation is decreasing. In 1959 the amplitudes were 1.361m and 0.957m in B and V, respectively (Schaltenbrand and Tammann 1971). In 1972-1974 the Figure 71 V and B-V curves of AS Per Figure 72 The composite B light curve of AS Per Figure 73 O-C diagram of AS Per amplitudes were smaller: 1.20m in B and 0.83m in V. In order to check the reality of this unique behaviour AS Per was reobserved in 1976-1977. The amplitudes were even smaller in this season. The composite B light curve is shown in Fig. 72. The decrease of the amplitude is about 0.01m/year in B light. Unfortunately, the unfavourable period prevents getting a complete light curve during one observational season. Further continuous photometry is needed to study this interesting phenomenon. The O-C residuals have been computed with the formula: C = 2441723.934 + 4.972516d*E . The O-C diagram (Fig. 73) shows the constancy of the period. Table 42 O-C residuals for AS Per Obs.Max.J.D. E O-C Type w Source 2417522.706 -4867 +0.007d phg 0.5 Kukarkin (1949) 2418258.80 -4719 +0.17 phg 0.5 Oosterhoff (1935) 2418676.14 -4635 -0.18 phg 0.5 Oosterhoff (1935) 2419009.72 -4568 +0.24 phg 0.5 Oosterhoff (1935) 2420546.56 -4259 +0.57 phg 0 Oosterhoff (1935) 2421585.66 -4050 +0.42 phg 0 Oosterhoff (1935) 2423399.77 -3685 -0.44 phg 0 Oosterhoff (1935) 2423783.63 -3608 +0.53 phg 0 Oosterhoff (1935) 2425155.87 -3332 +0.26 phg 0.5 Oosterhoff (1935) 2425528.46 -3257 +0.01 vis 0.5 Guthnick (1928) 2425936.190 -3175 -0.006 vis 1 Beyer (1934b) 2425985.840 -3165 -0.081 vis 0.5 Rugemer (1933) 2426001.08 -3162 +0.24 phg 0.5 Oosterhoff (1935) 2426239.433 -3114 -0.086 vis 1 Beyer (1934b) 2426284.50 -3105 +0.23 phg 0.5 Oosterhoff (1935) 2426565.02 -3049 +2.29 vis 0 Lange (1931) 2426691.869 -3023 -0.149 vis 1 Rugemer (1933) 2426761.57 -3009 -0.06 phg 0.5 Oosterhoff (1935) 2426786.424 -3004 -0.072 vis 1 Beyer (1934b) 2426995.241 -2962 -0.101 vis 1 Rugemer (1933) 2427034.78 -2954 -0.34 phg 0 Oosterhoff (1935) 2428094.332 -2741 +0.064 vis 0.5 Ahnert (1947) 2428611.322 -2637 -0.081 phg 1 Kukarkin (1949) 2428631.23 -2633 -0.07 vis 0.5 Kukarkin (1949) 2436816.019 -987 -0.042 phel 2 Weaver et al. (1960) 2436821.041 -986 +0.008 phel 2 Oosterhoff (1960) 2439252.614 -497 +0.020 phel 2 Takase (1969) 2441723.922 0 -0.012 phel 3 present paper V Lacertae According to Oosterhoff (1960) there is a photometric companion at V Lac. Miller and Preston (1964) contradicted this statement. The ratios of light amplitudes in different colours do not confirm the presence of a companion (see Fig. 74). Figure 74 V, B-V and U-B curves of V Lac Figure 75 O-C diagram of V Lac Table 43 O-C residuals for V Lac Obs.Max.J.D. E O-C Type w Source 2416716.392 -2445 -0.314d vis 0.5 Seares (1907b) 2417065.259 -2375 -0.289 vis 0.5 Seares (1907b) 2417353.6 -2317 -1.0 vis 0 Blazhko (1907a) 2417399.097 -2308 -0.344 vis 0.5 Seares (1907b) 2417613.341 -2265 -0.389 vis 0.5 Seares (1907b) 2417782.809 -2231 -0.359 vis 0.5 Zeipel (1908) 2417783.5 -2231 +0.3 vis 0 Muller, Hartwig^1 (1920) 2418031.919 -2181 -0.424 phg 0.5 Robinson (1931b) 2419716.574 -1843 -0.179 phg 1 Martin, Plummer (1916) 2420070.390 -1772 -0.189 phg 2 Martin, Plummer (1916) 2420578.848 -1670 -0.045 vis 0.5 Doberck (1920b) 2420633.512 -1659 -0.199 phg 2 Martin, Plummer (1916) Table 43 (cont.) Obs.Max.J.D. E O-C Type w Source 2420817.920 -1622 -0.181d phg 2 Hertzsprung (1922) 2421266.507 -1532 -0.106 vis 0.5 Doberck (1920b) 2421844.515 -1416 -0.180 phg 2 Jordan (1929) 2421884.427 -1408 -0.136 vis 0.5 Doberck (1920b) 2422203.529 -1344 +0.024 vis 0.5 Doberck (1920b) 2423334.721 -1117 -0.031 vis 0.5 Doberck (1924b) 2423698.370 -1044 -0.175 vis 0.5 Doberck (1924b) 2425836.327 -615 -0.126 vis 0.5 Parenago (1938) 2426324.847 -517 +0.014 vis 0.5 Terkan (1935) 2426529.094 -476 -0.061 vis 0.5 Kukarkin (1940) 2426558.980 -470 -0.076 phg 1 Zonn (1933) 2426758.428 -430 +0.033 vis 0.5 Dziewulski^2 (1947) 2426818.224 -418 +0.028 vis 0.5 Dziewulski (1947) 2427092.226 -363 -0.061 phg 1 Zonn (1933) 2427281.593 -325 -0.066 vis 0.5 Florya, Kukarkina (1953) 2428173.748 -146 +0.048 vis 0.5 Gur'yev (1938) 2428283.296 -124 -0.040 phg 0.5 Dziewulski et al. (1946) 2428353.125 -110 +0.020 phg 0.5 Dziewulski et al. (1946) 2428423.09 -96 +0.22 phg 0.5 Fu (1964) 2428557.460 -69 +0.033 phg 0.5 Dziewulski et al. (1946) 2429045.74 +29 -0.07 phg 0.5 Kurochkin (1946) 2433635.445 +950 -0.136 phg 1 Solov'yov (1952b) 2434393.169 +1102 +0.101 phg 0.5 Nikulina (1970) 2436794.894 +1584 -0.205 phel 3 Weaver et al. (1960) 2436809.829 +1587 -0.221 phel 2 Oosterhoff (1960) 2436834.777 +1592 -0.191 phel 2 Bahner et al. (1962) 2437348.104 +1695 -0.160 phel 2 Mitchell et al. (1964) 2437422.781 +1710 -0.235 phg 1 Golovatyj (1964) 2437487.567 +1723 -0.234 phg 0.5 Nikulina (1970) 2438070.607 +1840 -0.260 phg 1 Golovatyj (1964) 2438474.068 +1921 -0.460 phg 0.5 Nikulina (1970) 2439754.969 +2178 -0.310 phel 2 present paper^3 2441907.688 +2610 -0.449 phel 3 present paper Remarks: 1 Observer: Hartwig; 2 Obs.: Iwanowska; 3 Obs.: Abaffy. The O-C residuals have been computed with the formula: C = 2428901.286 + 4.983468d*E . The O-C diagram (Fig. 75) can be represented by a negative parabola: C_{par} = 2428901.286 + 4.983468d*E - 6.7d*10^{-8}*E^2 This representation of O-C residuals contradicts Parenago's (1956) statement that only sudden period changes can exist at the cepheids. GENERAL REMARKS Period changes The investigation of period changes of cepheids is of a great importance because an observational test of the cepheid evolution theory becomes possible by means of such investigations. The larger the number of epochs during which the observations have been made the more probable the detection of some evolutionary features on the basis of the observed period changes. Parenago (1956) investigated period changes of 42 cepheids selected arbitrarily. His sample contains only 7 cepheids with periods less than 5 days, and, the O-C diagrams published by him are not correct in the case of BL Her, SW Tau, BY Cas, SU Cyg and XY Cas. Since 1956 many cepheids have changed their period. As photoelectric photometry has become general in the last decades, it has been possible to determine the recent period changes more accurately. The present study on the period changes of cepheids based on uniformly constructed O-C diagrams has therefore uncovered a number of previously unnoticed phenomena. However, Parenago's statements concerning the statistics of period changes are correct (cf. page 110). Parenago found that the period changes were always sudden, i.e. the O-C diagram for a cepheid variable consists of straight lines. Detre (1970) distinguished three kinds of O-C diagrams for cepheids: 1. Those showing an evolutionary characteristic (parabolic curve), assuming that a cepheid changes its period while crossing the instability strip. Among cepheids with a period of less than 5 days there is only one star with an obviously parabolic O-C graph, viz. V Lac (see Fig. 75); 2. Those showing constant period. The number of cepheids with constant period diminishes continuously because each cepheid will change its period within a certain time; 3. Those showing irregular fluctuations of the period. Detre did not state that only sudden period changes could exist. The O-C diagrams presented in the previous section have shown that the period changes are sudden in the overwhelming majority of cases. As a matter of fact the straight lines may be distorted because of the period noise. Moreover, the velocity of the period change is unknown, i.e. we do not know the real shape of the O-C diagrams at the intersections of these straight lines. Therefore, we only approximate the O-C diagrams with straight lines. Besides the parabolic O-C curve of V Lac only AU Peg and possibly BL Her show an O-C graph which cannot be represented by straight lines. However, these latter two stars are Population II cepheids. Several cepheids which changed their period more than once have very interesting gradual, "stepwise" O-C variations. The original value of the period changed at a certain moment and in a short or somewhat longer time the period returned to its original value. Such a rejump may take place so suddenly (e.g. SU Cyg in Fig. 44) that the value of the intermediate period cannot be determined. If the rejump of the period is slower (e.g. V 532 Cyg in Fig. 31) the two opposite period jumps are well observable. In the case of SZ Tau there are two intermediate periods before returning to the original value of the period. These stepwise period changes can best be seen in DT Cyg (see Fig. 16). DT Cyg has changed its period and returned to the original period at least four times. This kind of period change may well have an important role in checking the recent theory on the evolution of cepheids. Arp (1960) showed the path of cepheid evolution between the blue giants and the red supergiants to be very close to a period-equals-constant line for cepheids in Small Magellanic Cloud. Later, Efremov (1968a) constructed the composite colour-magnitude diagram for the galactic groups of stars containing cepheids. His composite diagram shows that the slope of the evolutionary path is close to the slope of lines of constant period for the galactic cepheids, as well. The stepwise O-C diagram can be interpreted as a result of the evolution of the cepheid along the line of a given (constant) period. The deviations from this constant period are marks of small period fluctuations. The existence of this kind of O-C diagram is observational evidence supporting the hypothesis on the evolution of cepheids along the lines of constant period. It is noteworthy that among RR Lyrae variables such kinds of period changes are very rare. Among the 195 field RR Lyrae variables investigated by Tsessevitch (1966), only two stars (UY Boo, AT Ser) showed a return to the earlier period. Among 117 investigated RR Lyrae stars in the globular cluster M3, three variables (V54, V81, V110) showed rejump of the period (Szeidl 1965). There is another phenomenon observable for SU Cyg (a cepheid with a rejumping period), which leads us to treat secular variations of the light curves. Secular variations of the light curves The difference between the O-C values before the period jump and after the rejump for maximum brightness (\Delta(O-C)_{max}) differs remarkably from \Delta(O-C)_{med} for median brightness in the case of SU Cyg (see Fig. 44). The time difference between the moments of a maximum and the preceding median brightness were equal to about 0.43d until the period jump and after the rejump became 0.35d . This means that the ascending branch of the light curve became considerably steeper than before the period jump. Secular variation in the shape of the light curve can be observed in the case of FF Aql as well. As is shown in Fig. 63, the moments of the median brightness either repeat themselves with a period somewhat less than the period determined from the maxima or they are repeated with the period valid for the maximum but with a period jump and rejump at an unknown time between J.D. 2426000 and J.D. 2433000. In the case of FF Aql the ascending branch of the light curve has become less steep either suddenly or continuously. The third case of the observed secular light curve variations is the amplitude decrease of AS Per. This very slight decrease (about 0.01 mag/year in B) may not mean that AS Per evolves out of the instability strip because the calculated decay time of the pulsation is not more than several years (Christy 1966). Moreover, the period of the light variation of AS Per is constant. This means that the star is in a quiet stage of its evolution. The physical causes of above-mentioned sudden period changes and secular light curve variations are not yet known. Cepheids with small amplitude The first problem connected with these cepheids is the separation of cepheids with apparently small amplitude (photometric effect because of a companion) from the group of cepheids with really small amplitude. Cepheids with a nearly symmetrical light curve are undoubtedly true members of the group containing cepheids with small amplitude, since cepheids with large amplitude and nearly symmetrical light curve do not exist (except some cepheids with a period of 9-10 days for which the symmetrical light curve is caused by the presence of a bump). In order to decide whether a cepheid with small amplitude and light curve consisting of a steep rising branch and a less steep descending branch belongs either to large amplitude variables with apparently decreased amplitude or to small amplitude variables, spectroscopic observations of good quality are necessary. Spectroscopic observations are recommended in the cases of IR Cep and V 508 Mon. The second and more important problem concerning the small amplitude cepheids is their evolutionary status. According to Efremov (1968b) these stars have not yet reached the red supergiant stage, they are just crossing the instability strip for the first time. A great many arguments support this hypothesis. However, the theoretical calculations on the crossing time predict far fewer small amplitude cepheids compared with the other classical cepheids (Hofmeister 1967). If the first crossing were slower, the number of observable small amplitude cepheids would be greater. According to the theory of cepheid evolution the period of a cepheid must increase during the first crossing of the instability strip. During a given time interval the calculated change in the period is about a hundred times larger at the first crossing by comparison with other crossings of larger serial numbers in the case of low and intermediate cepheid masses (Hofmeister 1965). The cepheids with periods of less than five days are not massive for cepheids. The period changes determined from the O-C diagrams show much less difference between the ratios of period variation for small amplitude cepheids (first crossing) and large amplitude cepheids (second, third and other crossings). Let \DeltaP be the difference between the new and old values of the period at any period change. The relative change of the period is |\DeltaP|/P \approx 0.00011 for small amplitude cepheids averaged from 14 individual values. Seven variables showed no period changes. The three small amplitude cepheids showing both period jump and rejump are considered as cepheids with constant period, as well. The value |\DeltaP|/P for large amplitude classical cepheids is equal to 0.000007 (averaged from 17 values). Thus the relative period variation for small amplitude cepheids is only 10-20 times larger compared with the relative period variation for large amplitude classical cepheids. This can be explained in two different ways. Either the small amplitude cepheids evolve more slowly than predicted by the theory or the period variation does not mean the evolution of the cepheids - if these variables evolve along a path close to the lines of constant period. The latter case is more probable on the basis of O-C diagrams showing a rejumping period. Of course, in this case the rapid evolution (i.e. the short crossing time) at the first crossing takes place without greater period changes. However, the individual changes in period of small amplitude cepheids are usually much larger than in the case of large amplitude ones. The instability of the period Parenago (1956) suggested a new quantity \Delta E*|\Delta P|/P , which is characteristic of the instability of the period. Here \Delta E is the number of epochs during which the period remained constant. Table 44 gives a short summary on the instability of the period for different groups of cepheids. The successive columns contain the following data: 1. Name of the group 2. Average value of \Delta E*|\Delta P|/P 3. Average value of \Delta E 4. Average value of period of cepheids on which basis the preceding parameters are derived 5. Number of investigated cepheids in this group 6. Abbreviation of the name of the group in Table 45. Table 44 Group \overline{\Delta E*|Delta P|/P} \overline{\Delta E} \overline P n Abbrev. Classical cepheids 0.03 4000 4.1d 17 I with large amplitude Classical cepheids 0.26 2400 3.1 14 Is with small amplitude W Vir type variables 0.15* 5500 2.6 6* II The asterisks in Table 44 denote that AU Peg is omitted from among W Vir stars because its extremely large period changes would distort the statistics. Parenago derived 3-4 times larger values for \Delta E*|\Delta P|/P. He obtained 0.10 and 0.54 for the I and II groups, respectively. This systematic difference between his results and mine can be understood easily. The average period of cepheids investigated by Parenago is longer than 10 days (for both I and II groups), and it is well known that the longer the period, the greater its instability. Summary of the observations The fundamental parameters of the light variation of the observed cepheids are summarized in Table 45. The successive columns contain the following data: 1. Name of the cepheid 2. Period of light variation 3-4. The moments of the normal maximum and normal median brightnesses derived from the observations listed in Table 3 5-7. The maximum and minimum magnitudes and the amplitude in V 8-10. The corresponding quantities for B as under 5-7 11-13. The corresponding quantities for U as under 5-7 14. Type of cepheid Acknowledgements I am indebted to Dr. Bela Szeidl, Director of the Konkoly Observatory, for suggesting this investigation, for many valuable discussions and for his continuous interest. I should like to thank the night assistants of the Konkoly Observatory for helping in the observations. My special thanks are extended to Drs Table 45 Summary of the observations Name Period Norm.Max. Norm.Med. V_{max} V_{min} A_V B_{max} B_{min} A_B U_{max} U_{min} A_U Type Hel.J.D.2440000+ DQ And 3.200557d 1994.943 1994.620 11.27m 12.03m 0.76m 11.76m 12.84m 1.08m II FF Aql 4.470916 1576.428 1575.542 5.21 5.57 0.36 5.89 6.36 0.47 6.33m 6.91m 0.58m Is V 572 Aql 3.767697 1921.259 1920.415 11.01 11.42 0.41 11.87 12.50 0.63 II Y Aur 3.859502 1715.364 1715.010 9.17 9.99 0.82 9.87 11.04 1.17 I RT Aur 3.728190 1723.675 1723.247 5.01 5.82 0.81 5.43 6.60 1.17 5.72 7.08 1.36 I SU Cas 1.949322 1645.910 1645.532 5.76 6.13 0.37 6.32 6.88 0.56 6.79 7.42 0.63 Is SY Cas 4.071098 1682.236 1681.792 9.42 10.18 0.76 10.20 11.31 1.11 I XY Cas 4.501697 2006.786 2006.239 9.61 10.19 0.58 10.58 11.40 0.82 I BD Cas 3.650900 1932.032 1931.225 10.84 11.16 0.32 12.34 12.79 0.45 II BY Cas 3.223316 1774.189 1773.395 10.18 10.58 0.40 11.32 11.86 0.54 Is DF Cas 3.832472 1719.659 1719.230 10.53 11.12 0.59 11.49 12.36 0.87 I V 395 Cas 4.037728 1949.427 1949.027 10.39 10.95 0.56 11.39 12.20 0.81 I IR Cep 2.114124 1696.580 1696.248 7.58 7.98 0.40 8.28 8.86 0.58 8.70 9.39 0.69 Is* BD+56—2806 2.80591 2676.397 2675.735 9.26 9.56 0.30 10.07 10.53 0.46 Is SU Cyg 3.845492 1778.935 1778.589 6.45 7.17 0.72 6.83 7.86 1.03 7.17 8.34 1.17 I VZ Cyg 4.864453 1705.698 1705.089 8.60 9.24 0.64 9.32 10.29 0.97 9.74 11.00 1.26 I DT Cyg 2.499082 1737.798 1737.238 5.62 5.93 0.31 6.04 6.49 0.45 6.27 6.76 0.49 Is V 402 Cyg 4.364836 1698.635 1698.050 9.54 10.18 0.62 10.47 11.27 0.80 I V 532 Cyg 3.283612 1706.559 1705.882 8.97 9.31 0.33 9.90 10.41 0.49 Is V 1154 Cyg 4.925460 1494.442 1493.555 8.95 9.36 0.41 9.72 10.34 0.62 10.35: 11.26 0.91: Is Table 45 (cont.) Name Period Norm.Max. Norm.Med. V_{max} V_{min} A_V B_{max} B_{min} A_B U_{max} U_{min} A_U Type Hel.J.D.2440000+ V 1334 Cyg 3.333020d 1760.900 1760.240 5.78m 5.95m 0.17m 6.31m 6.52m 0.21m 6.48m 6.69m 0.21m Is AD Gem 3.787980 1694.911 1694.555 9.59 10.23 0.64 10.08 10.99 0.91 I BB Gem 2.308207 1839.700 1839.520 10.75 11.74 0.99 11.28 12.55 1.27 II DX Gem 3.137486 1866.668 1866.047 10.53 10.89 0.36 11.39 11.86 0.47 Is BL Her 1.3074502 1841.293 1841.180 9.78 10.60 0.82 10.02 11.13 1.11 II V Lac 4.983123 1907.688 1907.204 8.41 9.32 0.91 9.09 10.45 1.36 9.53 11.23 1.70 I Y Lac 4.323776 1746.745 1746.278 8.74 9.44 0.70 9.27 10.28 1.01 9.78 10.94 1.16 I BE Mon 2.705510 1880.240 1879.932 10.25 10.84 0.59 11.17 11.98 0.81 I V 465 Mon 2.713176 1698.687 1698.131 10.20 10.56 0.36 10.80 11.36 0.56 Is V 508 Mon 4.133608 1732.070 1731.528 10.32 10.74 0.42 11.05 11.68 0.63 Is* AU Peg 2.40142 1739.439 1738.920 9.11 9.46 0.35 9.78 10.29 0.51 10.11 10.80 0.69 II SX Per 4.289967 1847.979 1847.601 10.68 11.43 0.75 11.60 12.77 1.17 I AS Per 4.972516 1723.934 1723.397 9.14 9.97 0.83 10.39 11.59 1.20 I ST Tau 4.034299 1761.963 1761.507 7.79 8.55 0.76 8.47 9.58 1.11 8.95 10.23 1.28 I SW Tau 1.583584 1687.773 1687.418 9.37 10.16 0.79 9.82 10.88 1.06 10.05 11.26 1.21 II SZ Tau 3.148380 1659.194 1658.491 6.35 6.71 0.36 7.10 7.62 0.52 7.52 8.13 0.61 Is EU Tau 2.10248 1704.785 1704.360 7.94 8.28 0.34 8.57 9.03 0.46 9.02 9.60 0.58 Is T Vul 4.435462 1705.121 1704.584 5.40 6.06 0.66 5.90 6.83 0.93 6.14 7.30 1.16 I * Small amplitude, but non-sinusoidal light curve Katalin Barlai, Katalin Olah and Sandor Kanyo for useful discussions, and to Mrs. E. 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