COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                   Number 2142

                                Konkoly Observatory
                                Budapest
                                1982 May 11

                                HU ISSN 0374-0676



     NEW MINIMUM TIMES OF THE W UMA STAR SW LACERTAE




SW Lac is well known to have a variable period (see
e.g. Panchatsaram and Abhyankar, 1981 and the references
therein). In 1977, a sudden period change was observed
(Mikolajewska and Mikolajewski, 1981).
We made new photoelectric measurements of SW Lac in 1980
with the 75 cm telescope of the Wilhelm Foerster Observatory 
Berlin and in 1981 with the 106 cm and the 36 cm
Cassegrain telescopes of the Observatorium Hoher List. The
75 cm telescope is equipped with a single channel, uncooled
photometer with an 1P21 photomultiplier, standard UBV 
filters and an integrating amplifier. As integration time we
used 10 seconds. The 106 cm telescope is equipped with a
double beam, uncooled photometer with two 1P28B photomultipliers,
standard UBV filters and integrating amplifiers.
The 36 cm telescope has an uncooled, single beam photometer 
with an 1P21 photomultiplier, standard UBV filters
and a usual DC amplifier.
From our B and V measurements, we determined five times
of secondary minima by the Pogson method. They are listed
in the table. The O-C values are calculated with the 
ephemeris of Kreiner and Frasinka (1977):

  t_min,hel = 2442697.404d + 0.320724716d * E.       (1)

Table : New photoelectric minima times of SW Lac
Jul. Date_hel   C    n     E           O-C   telescope

2444 444.5211d  b   67
                        5447.5      - 0.0307d  75 cm
     444.5213   v   67
     816.5570   b   19  6607.5      - 0.0356  106 cm
     852.4793   b   58
                        6719.5      - 0.0349   36 cm
     852.4784   v   58
     853.4400   b   48
                        6722.5      - 0.0352   36 cm
     853.4414   v   49
     854.4045   b   22
                        6725.5      - 0.0348   36 cm
     854.4021   v   25


C: colour, n: number of individual measurements, E:
epoch according to (1). The error of each individual
determination is about 0.0005d, E and O-C are calculated
for the unweighted mean values of the minima times in
b and v.

                      [FIGURE 1]

The figure shows the resulting O-C diagram of all 
(photoelectrical) minima which were collected from Panchatsaram
and Abhyankar (1981), Aslan et al. (1981), Pohl and Gulmen 
(1981), Margrave (1982) and the values of the table.
Since the period jump in 1977, no further period change
occured. A discussion of the lightcurves will be given
elsewhere.




                  U. HOPP
                  Institut fur Astronomie und Astrophysik, 
                  Technische Universitat Berlin, 
                  Ernst Reuter Platz 7
                  D 1000 Berlin 10, FRG


                  M. HOFFMANN
                  Observatorium Hoher List
                  D 5568 Daun/Eifel, FRG
                  
                  S. WITZIGMANN
                  Wilhelm Foerster Sternwarte
                  Munsterdamm 90
                  D 1000 Berlin 41, FRG




References:
Aslan, Z., Asir, A., Engin, S., Tufekcioglu, Z., Yilmaz, N.:
        1981, Inf.Bull.Variable Stars No. 1908
Kreiner, J.M., Frasinka, Z.: 1977, Inf. Bull. Variable Stars No. 1285
Margrave, T.E.: 1982, Inf. Bull. Variable Stars No. 2086
Mikolajewska, J., Mikolajewski, M.: 1981, 
	Inf. Bull. Variable Stars No. 1953
Panchatsaram, T., Abhyankar, K.D.: 1981, Bull. astr. Soc.
        India 9. 31 [BIBCODE 1981BASI....9...31P ]
Pohl, E., Gulmen, O. 1981, Inf. Bull. Variable Stars No. 1924