COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3487

                                             Konkoly Observatory
                                             Budapest
                                             29 June 1990

                                             HU ISSN 0374 - 0676


    THE DISAPPEARANCE OF MINIMA OF ECLIPSING BINARY SS Lac IN
                      OPEN CLUSTER NGC 7209


   The eclipsing binary SS Lac = BD+45d3782(9.4) = 125.1907 is situated in
open cluster NGC 7209. The variability of the star was found by Hoffmeister
(1921), more exact light elements are given by Dugan and Wright (1935):
             Min I = 2415900.76+14.41629d * E
The change of brightness of the variable happens in the interval 10.28 -
10.69 m(pg) with identical minima. The orbit of the system is eccentric, e =
0.11. All observations were made photographically and visually. The 
photometric parameters were derived from the photographic light curve by Dugan
and Wright (1935).
   UBVR photoelectric observations were carried out during 1984-89 on Mt.
Maidanak in the Uzbek SSR. Stars N1 and N3 from Hoag et al.'s (1961) catalogue 
were used as standard stars. We have got 192 measurements of the binary. 
The probable error of a single observation in V is 0.012m for U-B:
0.017m, for B-V: 0.012m, for V-R: 0.020m. The light curve of SS Lac based on
the above elements is shown in Figure 1. It shows full absence of the 
expected brightness weakening in both minima. For comparison the photographic
light curve of SS Lac is given in the lowest part of the Figure. The survey
of all observations of the star showed, that the minima were persistently
observed in 1890-1950. We have concluded that the minima of the binary began
to disappear in about 1952. The most probable reason of the disappearance of
the minima can be a sudden change in the orbital plane inclination or, less
probably, the disintegration of the binary. Both may be caused by the pas-
sage of a cluster member star near SS Lac. But this is not at all certain,
only a tantalizing possibility.


                              [FIGURE 1]


                       
                        MAMNUN M. ZAKIROV
                        and
                        ALIBEK A. AZIMOV

                  Astronomical Institute of the Uzbek Academy
                          of Science


References:
Dugan, R.S., and Wright, F.W.: 1935, AJ, 44, 150. [BIBCODE 1935AJ.....44..150D ]
Hoag, A.A., Johnson, H.L., Iriarte, B., Mitchell, R.I., Hallam, K.L.,
   Sharpless, S.: 1961, Naval Obs. Publ., XVII, part VII, 349. [BIBCODE 1961PUSNO..17....1H ]
Hoffmeister, C.: 1921, AN, 214, No.5113, S1. [BIBCODE 1921AN....214....1H ]