COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2025

                                  Konkoly Observatory
                                  Budapest
                                  1981 October 13

                                  HU ISSN 0374-0676


     A LIGHT CURVE OF THE ECLIPSING BINARY LU LACERTAE



    The variability of LU Lac was detected by Miller (Miller 
and Wachmann, 1973), who found, that the object is an
eclipsing binary of W UMa type with a period just below 0.3d.
Photoelectric observations of LU Lac were obtained in five
nights between May and August, 1981. The star was measured
with the double beam photometer at the 1.06m telescope of
Hoher List Observatory. The light curve was completed only
in B, but some observations were also made in V to determine
at least the colour difference between the variable and the
comparison star. The latter, BD+50d3680, is a redder object
than LU Lac (Delta B-V ~ 0.7m). So significant second order extinction 
corrections had to be applied.

                         [FIGURE 1]

              Fig. 1: B light curve of LU Lacertae


Times of minimum light were found at

JD hel.2444726.5380 O-C +0.0042d       Ep.37526.5
       2444815.4282     +0.0010d          37824.0
       2444843.3680     +0.0029d          37917.5

The O-C's were calculated according to the light elements
given by Miller and Wachmann (1973)
JD hel. Min. I = 2433513.5649+ 0.29880135 E
The deviation of the observations from these elements are
still small. Figure 1 shows the B light curve of LU Lac
relative to the comparison star (normal observations).
Larger scatter around phase 0.25 results from observations
at greater atmospheric extinction, when the star became quite
faint for a 1m telescope (m_pg 14.6...15.5). The primary 
minimum is distinctly wider than the secondary minimum. So
LU Lac seems to be of W type with an occultation at the 
primary minimum, which is normal for contact binaries of its
period. A rectification of the light curve was tried with only 
a limited success. The eclipses are at least close to
completeness. The ratio of the radii has a lower limit k>=0.85
which indicates a mass ratio q>=0.75. As usual for short 
period W UMa stars the constancy of the light curve should be
checked at a later time.





                    M. HOFFMANN

                Observatorium Hoher List
                5568 Daun / Eifel, BRD





Reference:

Miller, W. J., Wachmann, A. A., 1973, Ric. Astron. 8, No. 12 [BIBCODE 1971RA......8..211M ]