COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2781

                                       Konkoly Observatory
                                       Budapest
                                       27 August 1985

                                       HU ISSN 0374 - 0676


        NEW MINIMUM TIMES AND PERIOD CHANGES OF SW LACERTAE


  SW Lac is a W UMa type binary and well known to have a variable period
(see Panchatsaram and Abhyankar, 1981). A sudden period change in 1977 was
announced by Mikolajewska and Mikolajewski (1981).
  The photoelectric observations of the system were made on seven nights
from July 15 to 27, 1985 at the Ege University Observatory. The 48 cm Cassegrain
reflector equipped with an EMI 9781 A photomultiplier, B, V filters and a
usual DC amplifier were used at the observations. BD+37deg4715 and BD+37deg4711
were chosen as comparison and check stars, respectively.

  From these observations two times of secondary and six times of primary
minima were determined. They are listed in the following table. The O-C 
values are calculated with the ephemeris of Kreiner and Frasinka (1977);

           Min I= JD Hel. 2442 697.404+0.320724716d.E.
  Hopp et al. (1982) noted that no period change has been occurred since the
period jump in 1977. We collected all the available O-C values obtained since
June 1968 and plotted in Figure 1. Some of the O-C values obtained visually
and published in BBSAG were grouped and shown as circles in this figure.
From this figure it is seen that the variations of the O-C values against
the epoch numbers may be separated into two parts: viz. 1800<E<4300 and
4300<E<11200. In this case linear light elements agree well with the O-C
values. An application of the least squares to these parts gave the following
ephemeris:

           for the first segment, 1800<E<4300

           Min I= JD Hel. 2442 697.3885+0.320722939d.E
                                 +/-30     +/-1068
           for the second segment, 4300<E<11200

           Min I= JD Hel. 2442 697.4018+0.320719765d.E.
                                 +/-11          +/-124


It seems, from the Figure 1 that two jumps have been occurred in the period of
SW Lac: the first at about 1977 and the second about July 1979.
  Naturally, we are interested in the behaviour of light curves of the system.
For this reason the system will be monitored in coming months and the resultant
light curves and their variations will be presented and discussed elsewhere.


                                [FIGURE 1]


                       Table I
          New photoelectric minima times of SW Lac

   Hel. J.D.   O-C          E         Colour
   2446000+
   262.3636  -0.0560d       11115.5   b
      .3633    .0563        11115.5   v
   264.4470    .0573        11122     b
      .4467    .0576        11122     v
   270.3797    .0580        11140.5   b,v
   270.5404    .0577        11141     b
      .5408    .0573        11141     v
   271.5028    .0574        11144     b
      .5030    .0572        11144     v
   272.4656    .0568        11147     b
      .4655    .0570        11147     v
   273.4271    .0575        11150     b
      .4268    .0578        11150     v
   274.3887    .0581        11153     b
      .3891    .0576        11153     v



S. EVREN, M.C. AKAN and C. IBANOGLU

Ege University Observatory
Bornova - Izmir,
Turkey

References :

Hopp, U., Hoffmann, M. and Witzigmann, S.: 1982, Inf.Bull. Variable Stars No. 2142.
Kreiner, J.M. and Frasinka, Z.: 1977, Inf.Bull. Variable Stars No. 1285.
Mikolajewska, J. and Mikolajewski, M.: 1981, Inf. Bull Variable Stars No. 1953.
Panchatsaram, T. and Abhyankar, K.D.: 1981, Bull astr.Soc. India 9, 31. [BIBCODE 1981BASI....9...31P ]