COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1503

                                Konkoly Observatory
                                Budapest
                                1978 November 13




         AN INCREASE IN THE PERIOD OF SW LACERTAE ?



   The W Ursae Majoris-type eclipsing binary system SW Lac (BD+37d4717)
is known for the depths of its eclipse curves, the variation in the shape
of its light curve, and its period behavior. Frasinska and Kreiner
(IBVS No. 1285, 1977) noted that after increasing during the interval 1893-
1968, the period decreased by 1.2 sec in the interval 1969-1973.
   One secondary and three primary eclipse curves of SW Lac were observed
photoelectrically in 1977 with the 40 cm telescope at North Georgia College,
Dahlonega. The photometer houses a thermoelectrically-cooled EMI 6256
photomultiplier and standard B and V filters. BD+37d4715 was observed as the
comparison star. The bisection-of-chords method was utilized to determine
the following epochs of minimum light.


JD Hel.
2443400+     Min.    O-C
--------------------------
59.7476       I    -0.1099
60.5490       II   -0.1103
87.6504       I    -0.1104
88.6128       I    -0.1102
--------------------------

The O-Cs were formed from the ephemeris given by Bookmyer (Astr. J. 70, 415,
1965). These O-Cs, and those formed from all other epochs of minimum light
observed photoelectrically within the past 15 or 16 years, are plotted versus
Hel. JD in Figure 1. Also included are 2 normal points representing 16
times of minimum light observed visually early in this season (BBSAG No. 38,
1978).
                          [FIGURE 1]

  Examination of the O-C curve shows there may have been a recent
increase in the period of SW Lac. Additional observations are needed
to confirm this. The following ephemeris,

       JD Hel. Min.I = 2443459.74760 + 0.3207216d E

is given to predict epochs of minimum light in the near future.
  The use of the observing facilities and the assistance of Dr. D.
Kinkaid, Dr. M. Davis, and students in the Department of Physics at North
Georgia College are acknowledged.


                           DANNY R. FAULKNER
                           BEVERLY B. BOOKMYER
                           Dept. of Physics and Astronomy
                           Clemson University
                           Clemson, SC 29631 USA