COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1427

                                                     Konkoly Observatory
                                                     Budapest
                                                     1978 May 15


          THE ORBITAL PERIOD VARIATION OF SZ Psc

The eclipsing and spectroscopic binary SZ Psc (HD 21913) is
known to show large period and light curve variations (Jakate et al.
1976). These authors found that the orbital period was decreasing
with a period derivative P = -(6.0+-0.5)*10^-8 days/day.
   Further observations made in the fall of the 1976 by Eaton
(1977) and in the fall of 1977 by the present authors at Catania
and Torino Observatory, show that the period is presently increasing.
   In Table 1 we give the observed epochs (t_obs) of primary
minima and O-C values computed according to the linear relation

          t_E = JD 2442308.946 + 3.9658663*E.


  t_obs        E      O-C     Remarks

25509.3950   -4236   -.1412   Jensch (1934)
25644.2780   -4202   -.0976   Jensch (1934)
25834.5070   -4154   -.2302   Jensch (1934)
25838.5040   -4153   -.1991   Jensch (1934)
25866.4230   -4146   -.0411   Jensch (1934)
26191.5220   -4064   -.1432   Jensch (1934)
26334.3650   -9028   -.0714   Jensch (1934)
27036.3650   -3851   -.0297   Jensch (1934)
27397.3800   -3760    .0915   Jensch (1934)
27421.2320   -3754    .1483   Rugemer (cfr.Jensch 1934)
27421.2530   -3754    .1693   Rugemer (cfr.Jensch 1934)
28000.2550   -3608    .1548   Gaposchkin (1943)
29935.8580   -3120    .4150   Gaposchkin (1952)
35741.8190   -1656    .3477   Jakate et al. (1976)
36114.5740   -1562    .3112   Jakate et a1. (1976)
42308.7671       0   -.1789   Jakate et al. (1976)
43117.7800     204   -.2027   From Eaton (cfr. IBVS 1297, 1977)
43998.5020     300   -.2039   present paper


   The mean period and starting epoch we assumed have been 
obtained by linear least square analysis of the observed epochs given
in Table 1. The epoch from Eaton's observations is largely uncertain
since only a limited portion of decreasing primary eclipse was observed. 
The epoch from Catania and Torino observations was determined 
as the average between the time of eclipse start and end. The
trend of O-C values shows that the non linear elements given by
Jakate et al. (1976) (represented by the continuous line in Fig. 1)
does not fit in with the present observations. It seems that the
period variations of SZ Psc may be better represented by a classical
sinusoidal curve. The amplitude of the O-C curve is about 0.6 day,
which is one of the largest known for eclipsing binaries.

                     [FIGURE 1]


                    S. CATALANO, A. FRISINA, M. RODONO

                    Osservatorio Astrofisico Catania


                          F. SCALTRITI

                    Osservatorio Astronomico Torino, Italy



References:

Jakate, S., Bakos, G.A., Fernie, J.D., Heard, J.F. 1976, Astron. J. 81, 250 [BIBCODE 1976AJ.....81..250J ]
Eaton, J.A. 1977, I.B.V.S. 1297
Jensch, A. 1934, Astron. Nachr. 252, 393 [BIBCODE 1934AN....252..393J ]
Gaposchkin, S. 1943, Harvard Ann. 113, No. 2
Gaposchkin, S. 1952, Harvard Ann. 118, No. 6