COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 533

                              Konkoly Observatory
                              Budapest  
                              1971 March 25



      A PHOTOELECTRIC MINIMUM OF THE ECLIPSING
             BINARY SZ CAMELOPARDALIS


      A secondary minimum of SZ Cam has been observed
with the 40 cm reflecting telescope of the Copenhagen
University Observatory at Brorfelde. A standard V filter
was used. The comparison star w as BD +61d 669 (B2) and the
check star was BD +61d 673 (A0), The extinction coefficient
determined from 52 observations of the comparison star was
applied to all observations. A single observation consisted
of five integrations of 14 seconds duration followed by two
integrations of the light from the night sky. From ten 
observations of the check star the standard deviation of a
single difference, check star minus comparison star, was
found to be 0.003m. The minimum consists of 49 differences
variable star minus comparison star, fairly evenly distributed 
within an interval of 0.45d. A preliminary determination
of the heliocentric julian date of the minimum, made by
mirroring the ascending branch on the descending branch,
gives JD_hel = 2 440 897.538d. The O-C residual from the
ephemeris by Wesselink (1941) is +0.111d (E=4952.5).
      As pointed out by Koch (1970) the spectral type by
Morgan et al. (1955) - B0II-III - prompts a conjecture of
mass loss and period changes. It should, however, be noted
that Murphy (1969) classifies SZ Cam as an O9V star.
       Assuming that the secondary minimum is separated
from the primary minimum by half the period, as found by
Wesselink (1941), a lengthening of the period seems to have
taken place. The mean period from 1934 to 1970 has been
2.6984390d. An observation of a primary minimum is needed to
determine if the secondary minimum is still situated at
phase 0.5p.

1971 March 17              ERIK HEYN OLSEN
                    Copenhagen University Observatory
                          Brorfelde, Denmark



REFERENCES:

Koch, R.H. 1970, Observational "facts" of binary mass loss,
    in Mass Loss and Evolution in Close Binaries, IAU Coll,
    no. 6, Eds. K. Gyldenkerne and R. West, Copenhagen University 
    Observatory, p. 65. [BIBCODE 1970mlec.coll...65K ]
Morgan, W.W., Code, A.D., Whitford, A.E. 1955, Ap.J.Suppl. 2,
    41.  [BIBCODE 1955ApJS....2...41M ]
Murphy, R.E. 1969, A.J. 74, 1082. [BIBCODE 1969AJ.....74.1082M ]
Wesselink, A.J. 1941, Ann, Sterrew. Leiden 17, part 3. [BIBCODE 1941AnLei..17C...1W ]