COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3596

                                               Konkoly Observatory
                                               Budapest
                                               3 May 1991

                                               HU ISSN 0374 - 0676


                  NEW PERIOD FOR GS Cep

    The eclipsing binary GS Cep (BD +57d2885) has been
observed photoelectrically at the N. Copernicus Observatory
and Planetarium in Brno with a 40 cm reflector. As already
noted by Hanzl (1990), most of the minima as predicted by the
ephemeris given in GCVS (Pri.Min. = HJD 2426350.375 + 0.772002d*E
did not appear. It was only possible to satisfy the measurements 
from the years 1988 and 1989 with a different period,
the preliminary value of which was 1.47162d [please note that
the date in Hanzl (1990), Table II, should read 715 instead of
716]. In order to check the new period, recent measurements
have been done during this year in V and B colours (by D.H.).
The results obtained are given in Table 1 (where also the times
of minima as reported by Hanzl (1990) are repeated). A new
ephemeris was calculated using LSM:

   Pri.Min. = HJD 2447414.4350 + 1.471625d*E
                          +-28        +-6


                   Table 1
              Photoelectric Data

 Time of minimum   Filter  Epoch     O - C
  HJD 2440000+

  7414.4346          V       0      -.0004
      .4346          B              -.0004
      .4359          U              +.0009
  7776.4546          V     246      -.0002
      .4539          B              -.0009
  8060.4838          V     439      +.0054
      .4845          B              +.0061
  8085.4996          V     456      -.0024
      .4936          B              -.0024
  8088.4365          V     458      -.0027
      .4358          B              -.0034
  8102.4205          V     467.5    +.0008
      .4198          B              +.0001


                         Table 2
                     Sonneberg Plates

HJD                              HJD
2400000+      Epoch      O-C     2400000+      Epoch      O-C

38242.524    -6232.5    -.007    41593.459    -3955.5     .032
38371.271    -6145.0    -.029    41596.385    -3953.5     .019
38410.297    -6118.5    -.001    41604.449    -3948.0    -.011
38557.507    -6018.5     .047    42306.408    -3471.0    -.017
38579.531    -6003.5    -.003    42359.363    -3435.0    -.040
38649.375    -5956.0    -.062    42601.506    -3270.5     .021
38813.272    -5844.5    -.240    42713.362    -3194.5     .033
39025.441    -5700.5     .004    42807.268    -3130.5    -.244
39053.389    -5681.5    -.009    42988.506    -3007.5    -.017
39059.378    -5677.5     .094    43008.394    -2994.0     .004
39063.395    -5674.5    -.303    43016.490    -2988.5     .006
39145.368    -5619.0    -.006    44116.492    -2241.0    -.030
39331.534    -5492.5    -.001    44195.280    -2187.5     .025
39359.469    -5473.5    -.027    44456.446    -2010.0    -.023
39443.363    -5416.5    -.016    44823.482    -1760.5    -.157
39671.467    -5261.5    -.013    44846.430    -1745.0    -.019
39685.482    -5252.0     .022    45138.502    -1546.5    -.065
39819.380    -5161.0     .001    45556.496    -1262.5    -.012
40145.382    -4939.5     .038    45674.271    -1182.5     .032
40173.311    -4920.5     .006    45935.436    -1005.0    -.016
40201.260    -4901.5    -.005    45946.374     -997.5    -.115
40476.461    -4714.5     .002    46373.289     -707.5     .029
40501.442    -4697.5    -.035    46648.464     -520.5     .010
40504.426    -4695.5     .006    46704.350     -482.5    -.026
40749.496    -4529.0     .051    46707.346     -480.5     .027
40827.448    -4476.0     .006    47094.342     -217.5    -.015
40914.297    -4417.0     .029    47139.224     -187.0    -.017
41512.483    -4010.5     .000


    It can be seen from the column O-C that the fit is very
good. The secondary minimum agrees with the ephemeris too,
i.e., the orbit is probably circular. The depths of the
primary and secondary minima are 0.4m (in both colours) and
0.3m, respectively; the width of both is 0.14d.


                       [FIGURE 1]

 Figure 1   O-C values for the star GS Cep. Dots ([dot]) represent 
 photographic and crosses (+) photoelectric observations


    For many years, the times of minima have been reported as
satisfactorily fitting the GCVS ephemeris [determined by
Strohmeier et al. (1962)]. Mr. Lichtenknecker kindly sent us
the list of all published photographic and visual minima. Some
of these 58 minima do agree with our ephemeris - among them
also one of two photographic minima observed by P. Frank (in
Huebscher et al. 1989). Two of us (P.N. , P.H. ) estimated the
brightness of the star on about 600 plates of the Sonneberg
Observatory collection, and found 55 plates with a lower
brightness than the rest. These times are listed in Table 2 and
illustrated in Figure 1 along with our measurements. With the
exception of nine of them, they agree with the new ephemeris
(O-C <= 0.050d). The older - mostly incorrect - visual data
probably can be explained by the low  amplitude of minima,
which is not suitable for visual estimations. The original
Bamberg data produced a rather suspicious light curve. The
reason why it shows such a large amplitude ( 0.9m in the
primary minimum) and why the period seemed well determined
remains unknown.


                              D. HANZL, P. NOVAK, P. HAJEK

                        N. Copernicus Observatory and Planetarium
                               Kravi Hora, 616 00 Brno


                                     Pavel MAYER

                        Department of Astronomy and Astrophysics
                                  Charles University
                               Svedska 8, 150 00 Praha 5
                                    Czechoslovakia


References:

Hanzl, D.: 1990, I.B.V.S., No. 3423.
Huebscher, J., Lichtenknecker, D., Wunder, E.: 1989, BAV Mitt. 52.
Strohmeier, W., Knigge, R., Ott, H.: 1962, Bamberg Veroff. 5, N. 15.