COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1237

                                                    Konkoly Observatory
                                                    Budapest
                                                    1977 February 10


      PERIOD CHANGES OF THE EARLY TYPE ECLIPSING
               BINARY SZ CAMELOPARDALIS

Five new minima of the eclipsing binary SZ Cam (HD 25638,
Sp. O9.5 V + B2?) were obtained photoelectrically with the 60cm
telescope at Skalnate Pleso Observatory in intermediate passband 
filters (halfwidth 195 A) centered at 4700 and 5200 A.
   All available minima are listed in Table 1.


                   Table 1

J.D. hel.    Minimum      E      O-C     Observer
2400000+                         days

27533.5191    prim.    0        0        Wesselink
40897.5387    sec.     4952.5   0.1114   Olsen
40911.0264    sec.     4957.5   0.1070   Kitamura-Yamasaki
40915.0722    prim.    4959     0.1052   Kitamura-Yamasaki
40924.5237    sec.     4962.5   0.1122   Olsen
41666.6009    sec.     5237.5   0.1249   Chochol
42762.2083    sec.     5643.5   0.1751   Chochol
42775.7037    sec.     5648.5   0.1784   Chochol
43076.5917    prim.    5760     0.1930   Chochol
43134.6074    sec.     5781.5   0.1927   Chochol

Predicted times of minima were calculated according to
Wesselink's ephemeris, (Wesselink, 1941):

        Min.= JD 2427533.5191+2.6984166 E.

   We assume that the secondary minimum is at the phase 0.5.
   As it is seen in the Figure, the original Wesselink's 
period does not agree with our measurements. The same problem
is with the revised period of Kitamura and Yamasaki (1972):
2.6984378 days. The new ephemeris as derived from Skalnate Pleso
measurements is:

           Min. = JD 2441666.6009+2.69854365 (E+0.5).

   It seems that there occurred an abrupt change of the period
around the year 1972. The increase of the period is probably due
to the change in the rate of mass transfer between the components.
The effects of mass transfer are seen quite well on the spectrograms 
taken in the years 1972-1975 in coude focus of the Ondrejov
2 m telescope.
   The interpretation of spectroscopic and photometric observations 
will be published in a forthcoming paper.


                        [FIGURE 1]

  O-C for SZ Cam based on the original Wesselink's period.



                        DRAHOMIR CHOCHOL

              Astronomical Institute Slovak Academy of
            Sciences, Tatranska Lomnica, Czechoslovakia


References:

1. Wesselink, A.J. 1941, Leiden Ann. 17, No. 3 [BIBCODE 1941AnLei..17C...1W ]
2. Kitamura, M., Yamasaki, A., 1972, Tokyo Astr. Bull. 220, 2563 [BIBCODE 1972TokAB.220.2563K ]