COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 2820

                                           Konkoly Observatory
                                           Budapest
                                           20 November 1985

                                           HU ISSN 0374 - 0676



            NEW MINIMUM TIMES AND PERIOD OF SW LACERTAE


  The W UMa-type star SW Lac (BD+37deg4717) is well known to have a variable 
period (see e.g. Panchatsaram and Abhyankar, 1981). The system was
observed on September 30 and October 1-4, 1983, at Kryonerion Observatory,
Greece. The observations were made with a 48-inch Cassegrain reflector
and a two-beam multi-mode photometer. The two intermediate pass-band
filters used were selected to be in close accordance with the standard
U,B,V colour system.


  Six times of minima observed during this season were calculated by
the folding paper method and they are listed in Table I. The successive
columns contain the heliocentric times of minima, the differences (O-C)1
and (O-C)2, the filter used and remarks.




                          Table I


 HJD              (O-C)1        (O-C)2      Filter   Rem.
 2440000+                          
    5608.4174     -0.0445       +0.0002     B,V      Min II
    5609.3794     -0.0447       +0.0001     B,V      Min II
    5611.3038     -0.0446       +0.0001     B,V      Min II
    5611.4638     -0.0450       -0.0002     B,V      Min I
    5612.2660     -0.0446       +0.0002     B,V      Min II
    5612.4259     -0.0450       -0.0003     B,V      Min I


  The (O-C)1 values have been calculated with the ephemeris of Kreiner
and Frasinska (1977)



     Min I = JD Hel 2442697.404 + 0.320724716d E           (1)

while the (O-C)2 values have been computed with a new ephemeris


    Min I = JD Hel 2444499.5264 + 0.3207204d E              (2)
                            +-6         +-2


which has been determined by least squares method and by using the times
of minima listed in Table I, the ephemeris given by equation (4) of
Mikolajewska and Mikolajewski (1981) and the last three mean minimum
times of those given by Hopp et al. (1982).

   It results from the above equations (1) and (2) and equation (4) of
Mikolajewska and Mikolajewski (1981) that the period of SW Lac is undergoing 
fluctuations around an average value. A sudden period change in
1977 announced by Mikolajewska and Mikolajewski (1981) and another jump
in the period in 1979 was noticed by Evren et al. (1985). Our computations 
show that the new ephemeris given by equation (2) holds good for
the time interval 1980-83. A discussion of the light curves and the
determination of the elements of the system will be given elsewhere.



                       P.G. NIARCHOS

                       Department of Astronomy
                       University of Athens
                       Panepistimiopolis
                       GR-15771 Zografos
                       Athens, Greece.




References :


Evren, S., Akan, M.C. and Ibanoglu, C. : 1985, I.B.V.S. No. 2781.
Hopp, U., Hoffmann, M. and Witzigmann, S. : 1982, I.B.V.S. No. 2142.
Kreiner, J.M.,  Frasinska, Z. : 1977, I.B.V.S. No. 1285.
Mikolajewska, J. and Mikolajewski, M. : 1981, I.B.V.S. No. 1953.
Panchatsaram, T. and Abhyankar, K.D. : 1981, Bull. astr. Soc. India
   9, 31. [BIBCODE 1981BASI....9...31P ]