COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3443

	                                         Konkoly Observatory
        	                                 Budapest
                	                         9 March 1990
	
          	                                 HU ISSN 0374 - 0676


              OBSERVATIONS OF FOUR DHK RED VARIABLES

  Kaiser has found light variations in a number of stars not officially
designated as variables (Kaiser et al. 1990; see that reference for positions,
magnitudes, etc.). I have used the Harvard College Observatory photographic
plate collection to investigate the light changes of the red variables DHK 6, 8,
10, and 12. Figure 1 is a finding chart for DHK 10, which is not included in
the BD or SAO atlases. Light curves for all four stars appear in Figure 2.

DHK 6 = BD +23 3694, HD 344531, IRC +20415, NSV 12178 (Vul)

  DHK 6 is an independent discovery by Kaiser of a variable first reported by
Strohmeier et al. (1956) as BV 142. The spectral type is M0. Estimates on 116
blue plates of the Damon patrol series from 1972-1988 produce a light curve with
significant variations but no clear periodicity, supporting the tentative NSV
classification of type Lb (Kholopov et al. 1982).

DHK 8 = BD -2 5597, SAO 145577, IRC +00507 (Aqr)

  The spectral type is M5. Estimates on 124 blue plates of the Damon patrol
series, 1970-1988, indicate that this variable is type SR. Seven pairs of
maxima or minima yield a well-defined mean period of 343 +/-12 days (standard
deviation).

DHK 10 = IRC 00085, NSV 2622 (Ori)

  This is an independent discovery of a variable first reported by Neugebauer
and Leighton (1969) as varying from 6.10-6.69 in the I band. The spectral type
is M4. Estimates on 89 blue plates of the Damon patrol series, 1972-1988,
suggest periodic behavior, but each cycle differs in shape, amplitude, and
length. This variable is probably type SR, but the period is poorly defined at
about 200 +/-100 days.


                              [FIGURE 1]

 Figure 1. Finding chart for DHK 10.  A = BD -4 1235, SAO 132515, 6.4 m_v
                                      B = BD -4 1233, SAO 132509, 9.0 m_v


DHK 12 = BD +29 3730, HD 18680, SAO 68801, IRC +30391, NSV 12387 (Cyg)

  This is an independent discovery by Kaiser of a variable first reported by
Lee (1970), who measured a mean magnitude of 7.62 V, +1.70 B-V, and spectral
type of M4.0 III. Estimates on 114 blue plates of the Damon patrol series,
1972-1988, do not show variations significantly greater than the observational
scatter.
  However, variability is confirmed by my photoelectric measures (Table I)
with a 28-cm Schmidt-Cassegrain telescope and Optec SSP-3 photometer, using Phi
Cyg (4.69 V, +0.97 B-V) as the comparison star. Each observation is the mean of
three or four differential measures, corrected for extinction and transformed to
the Johnson V system.

                     Table I

HJD 2447796.550   +2.992 DeltaV    +0.011 sigma1
        802.538   +3.009           +0.015
        310.594   +3.039           +0.011
        821.547   +3.138           +0.004
        861.503   +2.820           +0.003
        869.505   +2.890           +0.012


                               [FIGURE 2]

    Figure 2. Photographic light curves for DHK 6, 8, 10, 12.


  Together, the photoelectric and photographic observations suggest that the
amplitude does not exceed 0.4m. The above observations show the star dimming by
0.15m in 25 days and brightening by 0.32m during the 40-day observational gap,
after which it was dimming again. This suggests that the type is SRb with a
period of about 60 days, rather than the slow, irregular variation of type Lb.
However, more extensive photoelectric observations are needed to confirm the
classification and define the period.
  Some of the information in this report was obtained from the SIMBAD data
retrieval system, database of the Strasbourg, France, Astronomical Data Center.
I wish to thank curator Martha Hazen for extensive use of the Harvard College
Observatory photographic plate collection, for this and other variable star
projects. Daniel H. Kaiser, the discoverer, provided computer graphing of the
light curves.


                            DAVID B. WILLIAMS
                            9270-A Racquetball Way
                            Indianapolis, IN 46260
                            USA

REFERENCES

Kaiser, D. H., Baldwin, M. E., and Williams, D. B., 1990, 
  Inform. Bull. Var. Stars No. 3442.
Kholopov, P. N., editor, et al., 1982, New Catalogue of Suspected Variable
  Stars, Nauka, Moscow.
Lee, T. A., 1970, Astrophys. J. 162, 217. [BIBCODE 1970ApJ...162..217L ]
Neugebauer, G., and Leighton, R. B., 1969, Two-Micron Sky Survey, California
  Institute of Technology/NASA. [BIBCODE 1969tmss.book.....N ]
Strohmeier, W., Kippenhahn, R., and Geyer, E., 1956, Kleine Veroff. Bamberg
  No. 15.