COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1219

                                             Konkoly Observatory
                                             Budapest
                                             1976 December 16

SHORT TERM PERIODICITY OF V1500 CYGNI IN JULY - AUGUST OF 1976

TV photometric observations of V 1500 Cygni (Nova Cygni
1975) were carried out at the Crimean Astrophysical Observatory
using a 0.5 meter telescope and the television pick up tube LI-
217 with a multialkali input photocathode. Special combination
of glass filters allowed to register practically only the 
continuum radiation (see Fig. 1).
   Date of observations, number of TV pictures, duration of
patrol and moments of extreme value of light variation are listed 
in Table 1.

Date         Number of  Duration of       Moments
1976         pictures     patrol        J.D.hel= 2442...
                                       min.      max.

July 23-24     865        2h27m         -      983.377d
     28-29     259        2 01          -      988.474
     29-30     579        2 12          -         -
Aug. 2-3       847        4 46       993.394m   993.456

   Summary    2550       11h26m

    The following method has been used for photometric calibration 
of TV pictures. Images of 8 artificial stars of known brightness 
(calibrating marks) have been projected on to the input
photocathode of TV pick up tube during the exposures of the Nova.
One brightness step of these marks was 0.1m -:- 0.2m.
   Visual estimates of the brightness of Nova and the comparison
star 1 (see Fig. 2) have been made in the scale of artificial
star's magnitudes. The star 2 was used as a control star.
   The period of short term variations of Nova has been 
calculated using observed moments of extreme brightness (see Table 1)
and moments published by Semeniuk et al. (1). Determination of
the moments of minima was more accurate than that of maxima 
owing to the observed light fluctuation of the Nova at maxima. The
period has been found for the interval of July 2-August 2. It
appears to be slightly less than the published ones (1,2,3).
   Examination of the data obtained showed the forms of 
neighbouring maxima were different. That was the reason for doubling
of the value of the period. Fig. 3. shows the light-curves of
Nova constructed with the elements

          T_0 = 2442962d.404 + 0.27664d E.

   The accuracy of each mark on the graph is about +-0.05m.
Fig. 3 shows shows variability of the peak brightnesses of the
Nova. The mean amplitude of light variations is about 0.45m. It
is also possible that the distance between two maxima is not
constant.
   Numerous TV observations obtained during ten days show
that Nova Cygni 1975 is probably a close binary system with
the period of light variations about 6.5 hours.
   The authors are grateful to Drs. R.E. Gershberg and
N.M. Shachovskoj for discussions.


                            V.V. PROKOF'EVA
                            A.N. ABRAMENKO

                      Crimean Astrophysical Observatory
                      of the Academy of Sciences of the
                                U.S.S.R.



References:

1  Semeniuk, I., Kruszewski, A., Shwarzenberg-Czerny, A., IBVS No. 1157, 1976
2  Tempesti, P., IBVS No. 1052, 1975
3  Marcocci, N., Messi, K., Natali, G., Rossi, L., Nature 259, 185, 1976 [BIBCODE 1976Natur.259..186M ]


                         [FIGURE 1]

  Fig. 1. Response curve of TV apparatus for a star of type G2. Filled
  rectangles show emission lines observed in summer of 1976 in the
  spectrum of V 1500 Cygni.


                         [FIGURE 2]

  Fig. 2. The chart of V 1500 Cygni region; 1 - comparison star,
  2 - control star.


                         [FIGURE 3]

  Fig. 3. Television light - curves of V 1500 Cygni obtained on
  July 23 (crosses), 28 (rhombes), 29 (open circles) and August 2
  (filled circles). Ordinates are stellar magnitudes of Nova minus
  that of star 1.