A MAGYAR MITTEILUNGEN
TUDOMÁNYOS AKADÉMIA DER
CSILLAGVIZSGÁLÓ STERNWARTE
INTÉZETÉNEK DER UNGARISCHEN AKADEMIE
KÖZLEMÉNYEI DER WISSENSCHAFTEN
BUDAPEST-SZABADSÁGHEGY
Nr. 57
MERLE F. WALKER
(Lick Observatory, U.S.A)
PHOTOELECTRIC OBSERVATIONS OF VV PUPPIS
Budapest, 1965
Contributions from the Lick Observatory, No. 179
Mitteilungen der Sternwarte Budapest, Nr. 57
PHOTOELECTRIC OBSERVATIONS OF VV PUPPIS
MERLE F. WALKER
LICK OBSERVATORY, UNIVERSITY OF CALIFORNIA
Received November 12, 1964
I. INTRODUCTION AND OBSERVATIONS.
The variability of VV Puppis was discovered by Van Gent (1931), who
found that the period of variation is 100 minutes. Subsequent photometric
observations by various observers indicated that the behavior of the star is
quite complex, but it was supposed that the object was an ultra-short period
RR Lyrae variable; a summary of these photometric investigations is given by
Herbig (1960). In 1960, spectroscopic observations by Herbig (1960) indicated
that instead of being a pulsating variable, the object is actually an ultra short-
period binary system, perhaps similar to the UX UMa class of binaries. Accurate
photoelectric observations of VV Pup are clearly of importance to permit a more
detailed comparison of this system with other short-period binaries.
Photometric observations were obtained on three nights in 1964, February
10, March 15, and March 20 (UT), using the 120-inch reflector. The photometer
employed a 1P21 photomultiplier tube, refrigerated with dry ice, and the
following filters: Yellow, Corning 3384, standard optical thickness; Blue, 1 mm
Schott BG 12 plus 2 mm Schott GG13; Ultraviolet, Corning 9863, standard optical
thickness. On February 10 and March 15, the measures were made using a
focal plane diaphragm 13" in diameter; on March 20 a diaphragm 11" in
diameter was used. Owing to the short period of VV Pup, continuous observations
were made, using an offset eyepiece to keep the star centered in the
diaphragm. Sky measurements were made each 5 minutes during continuous
monitoring in one color, and before or after each deflection during the three-
color measurements. No comparison stars were observed during the observations
of the variable. Before and after the measures of VV Pup, observations
of stars having known magnitudes and colors on the U, B, V system of Johnson
and Morgan (1953) were obtained, and these measurements were used
to determine the extinction and to convert the observations of VV Pup to
the U, B, V system. The observations are listed in Tables 1-3, and are plotted
in Figures 1-3.
The observed times of maximum light have been used to derive the
following improved elements for the light-variation:
Max = JD 2427889.6474 + 0d.0697468256 E.
These elements were used in computing the phases of the observations in
Tables 1-3 and Figures 1-3. The epoch used in the above elements is that
given by Thackeray, et al. (1950), and the improved value of the period is only
very slightly different from that given by him. This result probably tends
to confirm the constancy of the period reported by the earlier observers (see
Herbig 1960), but it must be kept in mind that phase shifts in the time of
maximum light of up to 0.1P have been reported (Herbig 1960), so that the
apparent agreement with the older elements could be fortuitous; a large number
of maxima should be observed to derive a definitive set of elements.
The light-curves indicate that in yellow light, the system is constant
within 0.1 mag. from phase 0.2P to 0.7P, just one-half of the period. In blue
and ultraviolet light, the brightness decreases by about 0.1 mag. from 0.2P
to 0.7P if the average of the first and second cycles observed on March 20 is
used. During the first cycle on this night, the brightness in blue and ultraviolet
remained constant from 0.2P to 0.4P, decreasing to a minimum at 0.7P thereafter.
Fig.1. Photoelectric observations of VV Pup on February 10, 1964 in yellow
light. Circles represent observations shifted one cycle to the left. Phases
computed from the elements given in the text.
The initial rise in brightness after 0.7P is nearly as rapid as the decline
before 0.2P. However, near the top of the rise differences in the shape of
maximum occur. Symmetric maxima and maxima with a sharp peak both
before and after the midpoint of the maximum at phase O.OP have been
observed. The light-curves also show that the height of the maximum decreases
with decreasing wavelength and increases with increasing brightness of the
system at minimum light. The heights of maximum, measured from the light
level at 0.65P, together with the date of observation and the minimum bright-
ness of the system in yellow (V) light, are listed in Table 4. The width of the
maximum appears to be the same in yellow and blue light; the number of
observations in ultraviolet light is too small to make a definitive measurement
possible. Color measurements are difficult owing to the rapid variations in
brightness of the system. However, by using smoothed curves and interpolating
Fig.2. Photoelectric observations of VV Pup on March 15, 1964, in yellow, blue,
and ultraviolet light. Symbols and phases as in Figure 1.
Fig. 3. Photoelectric observations of VV Pup on March 20, 1964, in yellow, blue,
and ultraviolet light. Symbols and phases as in Figure 1.
between successive observations, the approximate values of the colors
at different phases and for different values of the V magnitude at minimum
have been derived and are listed in Table 5. The color variations, of course,
reflect the shape of the light curve as a function of wavelength and magnitude
at minimum discussed above. Thus, Table 5 shows that B-V increases slightly
between phases 0.2P and 0.7P while U-B remains constant during this
interval. Both B-V and U-B become appreciably redder during maximum
due to the decrease in amplitude of the maximum with wavelength.
The light-curves show the existence of rapid, intrinsic variations throughout
the 100-minute cycle. The amplitude and frequency of these variations
appears to be a maximum during maximum light. Rapid fluctuations during
maximum have been noted previously (Thackeray et al. 1950; Oosterhoff
and Thackeray 1960). These variations have been studied on February 10
in yellow light, and on March 20 in blue light between phases 0.05P and 0.17P,
in order to determine whether rapid periodic variations occur similar to those
found previously in DQ Her (Walker 1956, 1958, 1961). The detection of a
rapid, periodic variation with an amplitude of the order of 0.05 mag. would
only be possible during maximum light; at minimum, such a variation would
be obscured by the noise owing to the faintness of the star. A number of maxima
and minima were found during maximum light. These were measured and are
identified in Tables 1 and 2 by a plus sign for a maximum and a minus sign
for a minimum. Attempts to represent them with a uniform period were only
partially successful. Most, but not all, of the variations could be represented
by a period of about 67 seconds. Departures from that period could result
from disturbances in the times of maximum and minimum due to the poor
signal-to-noise ratio even during maximum light, but it is also entirely possible
that the apparent periodic occurrence of these maxima and minima was only
fortuitous. The observations suggest, however, that a periodic variation may
be detectable in this object, and it is clearly of importance to obtain additional
observations in order to determine if this variation really exists. Another
feature of the light-curve, repeated during the two successive cycles observed
on February 10, is a small minimum which occurred at phase 0.225P. Apart
from these variations, the intrinsic variability of the system appears to be
completely random.
Table 1
VISUAL OBSERVATIONS
Helioc JD Helioc V Helioc JD Helioc V
2438000+ Phase Mag. 2438000+ Phase Mag.
435.8612 .0795 15.84 435.8886 .4724 17.11
.8623 .0953 15.76 .8890 .4781 17.09
.8626 .0996 15.70 .8893 .4824 17.10
.8629 .1039 15.68 .8897 .4882 17.13
.8633 .1097 15.67 .8900 .4925 17.13
.8636 .1140 15.74 .8904 .4982 17.14
.8647 .1297 15.84 .8907 .5025 17.15
.8650 .1340 15.91 .8911 .5082 17.15
.8654 .1398 16.04 .8925 .5283 17.17
.8657 .1441 16.13 .8928 .5326 17.17
.8661 .1498 16.20 .8932 .5383 17.18
.8664 .1541 16.24 .8935 .5426 17.19
.8668 .1598 16.35 .8939 .5484 17.19
.8671 .1641 16.48 .8942 .5527 17.20
.8675 .1699 16.66 .8946 .5584 17.19
.8678 .1742 16.82 .8949 .5627 17.20
.8685 .1842 17.10 .8967 .5885 17.17
.8689 .1899 17.20 .8970 .5928 17.16
.8692 .1942 17.23 .8974 .5986 17.13
.8696 .2000 17.27 .8977 .6029 17.03
.8699 .2043 17.26 .8981 .6086 17.10
.8703 .2100 17.25 .8984 .6129 17.15
.8706 .2143 17.26 .8987 .6172 17.15
.8710 .2201 17.26 .8990 .6215 17.15
.8720 .2344 17.28 .8994 .6272 17.15
.8724 .2401 17.28 .9004 .6416 17.17
.8727 .2444 17.27 .9008 .6473 17.14
.8731 .2502 17.23 .9015 .6573 17.14
.8734 .2545 17.20 .9022 .6674 17.14
.8737 .2588 17.19 .9025 .6717 17.14
.8740 .2631 17.15 .9029 .6774 17.17
.8744 .2688 17.12 .9032 .6817 17.20
.8747 .2731 17.09 .9036 .6874 17.20
.8761 .2932 17.11 .9039 .6918 17.21
.8765 .2989 17.14 .9060 .7219 16.93
.8782 .3233 17.11 .9064 .7276 16.95
.8786 .3290 17.11 .9067 .7319 16.95
.8789 .3333 17.11 .9071 .7376 16.96
.8793 .3391 17.11 .9074 .7419 16.99
.8807 .3591 17.10 .9078 .7477 17.02
.8810 .3634 17.11 .9081 .7520 17.03
.8814 .3692 17.10 .9102 .7821 17.00
.8817 .3735 17.11 .9106 .7878 16.99
.8821 .3792 17.11 .9109 .7921 16.99
.8824 .3835 17.11 .9112 .7964 16.93
.8828 .3892 17.14 .9115 .8007 16.86
.8831 .3935 17.14 .9117 .8036 16.83
.8835 .3993 17.12 .9118 .8050 16.96
.8838 .4036 17.09 .9119 .8065 16.81
.8849 .4193 17.08 .9120 .8079 16.59+
.8852 .4236 17.08 .9121 .8093 16.69
.8856 .4294 17.08 .9122 .8108 16.76-
.8859 .4337 17.09 .9123 .8122 16.63
.8862 .4380 17.09 .9125 .8151 16.42+
.8865 .4423 17.09 .9127 .8179 16.57
.8883 .4681 17.08 .9127 .8179 16.72-
Table 1(Continued)
Helioc JD Helioc V Helioc JD Helioc V
2438000+ Phase Mag. 2438000+ Phase Mag.
435.9130 .8222 16.53 435.9404 .2151 17.34
.9132 .8251 16.33+ .9407 .2194 17.33
.9134 .8280 16.41 .9411 .2251 17.33
.9135 .8294 16.50- .9425 .2452 17.24
.9136 .8308 16.43 .9428 .2495 17.20
.9138 .8337 16.32+ .9432 .2552 17.17
.9139 .8351 16.39 .9435 .2595 17.16
.9140 .8366 16.44- .9439 .2653 17.14
.9143 .8409 16.33 .9453 .2853 17.10
.9146 .8452 16.20+ .9456 .2896 17.09
.9148 .8480 16.25 .9460 .2954 17.20
.9164 .8710 16.08 .9493 .2997 17.09
.9165 .8724 16.18- .9467 .3054 17.01
.9167 .8753 16.06 .9484 .3298 17.07
.9168 .8767 15.85+ .9487 .3341 17.09
.9170 .8796 16.06 .9490 .3384 17.11
.9172 .8824 16.17- .9494 .3441 17.18
.9175 .8868 16.07 .9497 .3484 17.18
.9220 .9513 16.17 .9501 .3542 17.17
.9224 .9570 16.13 .9504 .3584 17.15
.9227 .9613 16.18 469.7941 .5949 16.43
.9231 .9670 16.04 .7948 .6049 16.53
.9234 .9713 15.98 .8031 .7239 16.41
.9237 .9756 15.94 .8047 .7468 16.10
.9251 .9957 15.98 .8069 .7784 15.57
.9254 .0000 16.02 .8076 .7884 15.59
.9258 .0058 15.97 .8149 .8931 14.82
.9259 .0072 16.05 .8159 .9074 14.57
.9261 .0101 16.11 .8194 .9576 14.77
.9264 .0144 16.01 .8208 .9777 14.76
.9265 .0158 15.93 .8239 .0221 14.75
.9270 .0230 15.94 .8281 .0823 14.76
.9272 .0258 15.87 474.6940 .8475 16.29
.9275 .0301 15.96 .6948 .8590 16.13
.9279 .0359 15.95 .7071 .0354 15.52
.9282 .0402 15.89 .7074 .0397 15.54
.9286 .0459 15.86 .7184 .1974 16.96
.9289 .0502 15.87 .7242 .2805 16.97
.9293 .0559 15.89 .7261 .3078 16.91
.9296 .0602 15.94 .7320 .3924 17.02
.9315 .0875 15.75 .7375 .4712 17.02
.9317 .0903 15.82 .7435 .5572 17.07
.9326 .1032 15.86 .7502 .6533 17.00
.9328 .1061 15.95 .7608 .7608 16.99
.9339 .1219 15.92 .7675 .9013 16.28
.9344 .1291 15.96 .7678 .9056 16.16
.9348 .1491 16.14 .7680 .9085 16.07
.9361 .1534 16.20 .7742 .9974 15.85-
.9364 .1577 16.26 .7746 .0031 15.65+
.9367 .1620 16.23 .7817 .1049 15.86
.9374 .1721 16.56 .7820 .1092 15.78-
.9376 .1749 16.64 .7883 .1996 16.99
.9379 .1792 16.88 .7912 .2411 16.98
.9383 .1850 17.23 .7978 .3358 17.30
.9386 .1893 17.52 .8041 .4261 17.17
.9397 .2050 17.35 .8102 .5136 16.95
.9400 .2093 17.35
Table 2
BLUE OBSERVATIONS
Helioc JD Helioc B Helioc JD Helioc B
2438000+ Phase Mag. 2438000+ Phase Mag.
469.7962 .6250 16.42 474.7194 .2117 16.83
.7969 .6350 16.44 .7223 .2533 16.93
.8009 .6924 16.44 .7236 .2719 16.89
.8026 .7167 16.42 .7261 .3078 16.97
.8047 .7468 15.98 .7307 .3737 16.90
.8066 .7741 15.89 .7334 .4124 16.92
.8081 .7956 l5.82 .7358 .4468 16.95
.8094 .8142 15.67 .7390 .4927 17.04
.8125 .8587 15.27 .7423 .5400 16.99
.8132 .8687 15.11 .7452 .5816 17.05
.8135 .8730 15.04 .7482 .6246 17.14
.8164 .9146 14.62 .7515 .6719 17.06
.8176 .9318 14.85 .7550 .7221 16.96
.8220 .9949 15.03 .7553 .7264 17.10
.8257 .0479 14.86 .7557 .7322 17.23
474.6955 .8690 16.19 .7567 .7465 17.18
.6966 .8848 15.94 .7570 .7508 17.11
.6984 .9106 15.88 .7589 .7780 17.01
.6987 .9149 16.05 .7591 .7809 16.97
.6996 .9278 15.97 .7594 .7852 16.78
.6998 .9307 15.88 .7598 .7909 16.91
.7001 .9350 15.82 .7601 .7952 16.82
.7005 .9407 15.82 .7605 .8010 16.78
.7008 .9450 15.82 .7615 .8153 16.78
.7081 .0497 15.80 .7619 .8211 16.70
.7084 .0540 15.69+ .7643 .8555 16.51
.7086 .0569 15.74 .7646 .8598 16.49
.7088 .0597 15.77- .7650 .8655 16.47
.7091 .0640 15.71 .7653 .8698 16.41
.7092 .0655 15.64+ .7666 .8884 16.28
.7094 .0683 15.78 .7690 .9229 16.09
.7095 .0698 15.83- .7692 .9257 16.06
.7099 .0755 15.78 .7695 .9300 16.00
.7100 .0769 15.77+ .7723 .9702 15.92
.7103 .0812 15.82 .7726 .9745 15.83
.7106 .0855 15.89- .7730 .9802 15.89
.7109 .0898 15.87 .7759 .0218 16.07
.7114 .0970 15.84+ .7761 .0246 15.95+
.7116 .0999 15.93 .7764 .0289 16.09
.7121 .1070 16.10- .7765 .0304 16.24-
.7127 .1156 16.05 .7769 .0361 16.12
.7130 .1199 16.00+ .7798 .0791 16.01
.7134 .1257 16.11 .7803 .0849 16.05
.7139 .1329 16.18- .7835 .1307 16.13
.7143 .1386 16.20 .7869 .1795 17.02
.7150 .1486 16.12+ .7928 .2641 16.99
.7154 .1544 16.34 .7963 .3143 17.06
.7157 .1586 16.45- .7993 .3573 17.22
.7157 .1586 16.42 .8028 .4075 17.09
.7158 .1601 16.39+ .8057 .4490 17.19
.7161 .1644 16.53 .8089 .4949 17.39
.7163 .1673 16.70 .8118 .5365 17.17
.7179 .1902 16.91
Table 3
ULTRAVIOLET OBSERVATIONS
Helioc JD Helioc U Helioc JD Helioc U
2438000+ Phase Mag. 2438000+ Phase Mag.
469.7975 .6436 15.67 474.7218 .2461 15.87
.8001 .6809 15.60 .7291 .3508 15.84
.8098 .8200 15.27 .7352 .4382 15.82
.8114 .8429 14.56 .7390 .4927 15.99
.8125 .8587 14.68 .7412 .5243 15.87
.8176 .9318 14.52 .7473 .6117 16.10
.8181 .9390 14.66 .7544 .7135 15.99
.8189 .9504 14.76 .7629 .8354 15.72
.8232 .0121 14.88 .7709 .9501 15.34
.8268 .0637 14.62 .7785 .0591 15.44
474.7022 .9561 15.07 .7851 .1537 15.73
.7032 .9794 15.24 .7942 .2842 15.96
.7037 .9866 14.95 .7945 .2884 16.13
.7043 .9952 15.11 .7948 .2928 16.21
.7046 .9995 15.13 .8007 .3774 16.10
.7050 .0052 15.16 .8070 .4677 16.14
.7205 .2275 15.89
Table 4
HEIGHTS OF MAXIMA OF VV PUP
Height of Maximum
Date Vmin (mag)
UT (mag)
V B U
1964
Feb. 10 17.1 1.4 - -
Mar. 15 16.4 1.8 1.6 1.0
Mar. 20 17.0 1.4 1.2 0.9
Table 5
COLORS OF VV PUP
B - V U - B
Phase
Vmin=16.4* Vmin=17.0** Vmin=16.4* Vmin=17.0**
0.2 - 0.00 - -1.1
0.5 - +0.05 - -1.1
0.7 +0.05 +0.05 -0.8 -1.1
1.0 +0.27 +0.30 -0.02 -0.8
* March 15, 1964
** March 20, 1964
II. DISCUSSION.
In color, shortness of period, and the occurrence of rapid intrinsic varia-
bility, VV Pup resembles the stars of the "UX UMa" class, which include:
UX UMa (Johnson, Perkins, and Hiltner 1954; Walker and Herbig 1954;
Krzeminski and Walker 1963), DQ Her (Walker 1956, 1958, 1961), RW Tri
(Walker 1963a), T Aur (Walker 1963b), WZ Sge (Krzeminski 1962), and U
Gem (Kraft 1962, Mumford 1962,1964). VV Pup also resembles these systems
in having, in blue and ultraviolet light, a shallow minimum near 0.7P. The
light-curve of VV Pup is particularly similar to that of U Gem, as noted by
Mumford (1964). This similarity is made more striking by the present obser-
vations. In both systems "minimum" light lasts just 0.55 of the period, with
some decrease in brightness between phases 0.2 and 0.7 in blue and ultraviolet
light (taking zero phase at maximum light). In both cases, the height of maxi-
mum decreases with decreasing wavelength, although the wavelength depend-
ence is smaller in U Gem than in VV Pup, the heights of maximum ranging
from 0.60 mag. in yellow and blue light to 0.50 mag. in ultraviolet light. The
colors of the two systems are also somewhat similar. At 0.7P, the colors of
U Gem are B-V = +0.5, U-B = - 0,7, and at 0.0P (maximum light),
B-V = +0.35, U-B = - 0,55 (Mumford 1964).
The light and velocity variations of VV Pup have been explained by
Herbig (1960) in terms of a model in which the brighter star is the larger and
has a bright spot on its surface displaced about 45deg from the subsecondary
point on the preceding hemisphere of the star. In U Gem, the fact that an
eclipse is observed about 0.15P after maximum light suggests that in this
system the brighter object consists of a small, hot star surrounded by some
sort of extended atmosphere or cloud which possesses a markedly non-uniform
surface brightness. The present observations suggest that the brighter star
in VV Pup may have a similar structure. As mentioned in Section I, small
minima in the light curve occurred at phase 0.225P during two successive
cycles on February 10. These minima were not observed on March 20. Owing
to the fact that measures in three colors were made, the coverage of this parti-
cular part of the curve is not intensive. Nevertheless, it would seem that
sufficient observations were obtained that some indication of the minima should
be visible had it existed. Despite the absence of the minima of March 20,
it appears possible that these minima could represent the partial eclipse of
a small hot star as in U Gem. The occasional absence of the eclipse might be
explained by veiling of the star by the surrounding material. It is interesting
to note that the minima on February 10 are slightly asymmetric, the actual
point of minimum light lying near 0.215P. The end of the minimum occurs
at 0.270P. If we suppose that mid-eclipse occurs at 0.215P, then first contact
should occur at 0.155P. Examining the light-curves, we find that just at this
phase, on February 10, the slope of the descent from maximum light increases;
for phases less than 0.155P, the slope matches the reflected slope of the rise
to maximum light. The same phenomenon can be observed in the light-curve
of March 20, except that on this night the change in slope occurs at phase
0.145P. The existence of this effect would appear to strengthen somewhat
the supposition that the minima at 0.225P (or 0.215P) represent eclipses
even though the spectroscopic observations (Herbig 1960) predict that mid-
eclipse should come at 0.29P. Clearly, further observations to determine whe-
ther this minimum is an eclipse, or was only a transitory feature lasting for
only two or more cycles on February 10, are highly desirable.
It is a pleasure to thank Dr. G. Chincarini and Mr. R. Freedman for their
assistance in the reduction of these observations.
REFERENCES
Herbig, G. H. 1960 Ap. J,. 132, 76.
Johnson, H. L., and Morgan, W. W. 1953, Ap. J., 117, 313.
Johnson, H. L., Perkins, B., and Hiltner, W. A. 1954, Ap. J. Suppl.,1, 91 (No.4).
Kraft, R. P. 1962, Ap. J., 135, 408.
Krzeminski, W. 1962, Pub. A. S. P., 74, 66.
Krzeminski, W., and Walker, M. F. 1963, Ap. J.,138, 146.
Mumford, G. S. 1962, Sky and Tel., 23, 135.
------ 1964, Ap. J.,139, 476.
Oosterhoff, P. Th., and Thackeray, A. D. 1960, Sky and Tel., 19, 337.
Thackeray, A. D., Wesselink, A. J., and Oosterhoff, P.Th. 1950, B. A. N., 11, 193
(No. 413).
Van Gent, H. 1931, B. A. N., 6, 93 (No. 214).
Walker, M. F. 1956, Ap. J.,123, 68.
------- 1958, ibid., 127, 319.
------- 1961, ibid., 134, 171.
------- 1963a, ibid., 137, 485.
------- 1963b, ibid., 138, 313.
Walker, M. F., and Herbig, G. H. 1954, Ap. J., 120, 278.