COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2196

                                 Konkoly Observatory
                                 Budapest
                                 1982 September 6

                                 HU ISSN 0374-0676





 EVIDENCE FOR THE VARIATION OF BRIGHTNESS WITHIN THE PRIMARY
           MINIMA IN W UMa (BD + 56d1400)


  Photometry of the star was carried out in Izmir, at Ege 
University Observatory with the 48 cm Cassegrain reflector and EMI
9781 A unrefrigerated photomultiplier. The first complete light
curve was obtained on January 6, 1982 with excellent sky conditions 
(k_B = 0.16, k_V = 0.19). On January 7, 1982 only the primary
minimum was repeated. Until the end of February, 1982 the variable
star could not have been observed due to bad weather conditions.
In March 25/26/28, 1982 one light curve was completed. The last
uncomplete light curve in this season was obtained in April 6,
1982.
  In previous bulletins (I.B.V.S. Nos: 2083, 2102, 2151) timings
of primary and secondary minima, corresponding (O-C) values were
calculated and presented together with the figures. Intercomparison 
among the light curves obtained in January, March, April
1982 and particularly between January and April has resulted in
conspicious brightness variation (see Figure 1). The light curves
obtained on January 16/17 and the last one obtained on April,
1982 exhibit marked brightness difference within the first
minimum, whereas corresponding brightness difference is not so
conspicious within the secondary minimum. The brightness difference 
within the first minimum is about 0.05 - 0.06 magnitude.
In order to check if this value is correct from the point of
view of observational errors, the comparison star (BD+56d1399)
was re-examined and its brightness constancy was checked throughout 
the observations. It is clear that the comparison star exhibits 
no variation what so ever and its standard mean error
was calculated for the nights and amounted to 0.01 magnitude.
 
                          [FIGURE 1]

Figure 1. Differential brightness curves of W UMa obtained in
January, March and April 1982. Dots, crosses and open
circles correspond to the observations obtained on
16/17 January, 1982, 25/26/28 March, 1982 and April 6,
1982 respectively. The dimension of circles (open or
filled) correspond to the standard mean error of 0.01
magnitude.

Therefore the brightness variation within the primary minimum is
real and is about 0.05-0.06 magnitudes between January and April,
1982.

Acknowledgements: I would like to thank Dr. E. Hamzaoglu and
Mr. T. Eker for the observations of the star.


                     M. HAMZAOGLU
                     Ege University Observatory, P.K. 21
                     Izmir - Turkey


References:

Tunca, Z., Tumer, O., Evren, S., 1979, I.B.V.S. No. 1607
Hamzaoglu, E., Keskin, V., Eker, T., 1982, I.B.V.S. No. 2083
Hamzaoglu, E., Keskin, V., Eker, T., 1982, I.B.V.S. No. 2102
Hamzaoglu, M., Hamzaoglu, E., Eker, T., 1982, I.B.V.S. No. 2151