COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2791

                                       Konkoly Observatory
                                       Budapest
                                       13 September 1985

                                       HU ISSN 0374 - 0676


           LIGHT CURVE VARIATION OF PZ CASSIOPEIAE

  The semi-regular variable star PZ Cassiopeiae was investigated using the
patrol plates of Odessa astronomical observatory seven-camera astrograph
obtained in 1957-1983. They were exposed through a yellow filter on the
emulsion ZP-3. The exposure time was 30 min.
  The times of light extrema observed are given in Table I. For them the
following elements were obtained (L.S. Kudashkina, Astron.Tsirk. No. 1351, 1984):
            Max JD = 2436809.6 + 801.3d E
            Min JD = 2437164.1 + 801.3d E
  The diagram for residuals (O-C) for the above elements is shown in Figure 1.
Maximum and the subsequent minimum have the same cycle number. Qualitative
similarity of (O-C) curves for maximum and minimum shows that cycle duration
is changing, possible in a regular way. The dependence of duration of the
ascending and descending branches on cycle number (which corresponds to the
nearest maximum) is shown in Figure 2. As these two curves are opposite in
phase, cyclicity (about 18 years) cannot be excluded. Ascending branch is
shorter than the descending one during half of this cycle but in the second
half of the cycle the situation is inverse.

                         Table I

     E   Max         O-C     Min       O-C

     0   2436900     91     2437180    16
     1      7600    -10        7940   -25
     2      8320    -22        8700   -67
     3      9000    -214       9610:   42
     4      9840    -175    2440520    151
     5   2440800    -16        1220    49
     6      1600    -17        1980    8
     7      2680:    162       2800    27
     8      3400     180       3600:   26
     9      4120     99        4360:  -16
    10      4800    -23        5260:   83
    11      5660     36


  Author is grateful to Yu.S. Romanov and I.L. Andronov for useful discussions.


                               [FIGURE 1]
                               [FIGURE 2]



L.S. KUDASHKINA
Odessa State University             
T.G. Shevchenko Park
Odessa 270014 USSR