COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                   Number 1978

                                 Konkoly Observatory
                                 Budapest
                                 1981 June 19

                                 HU ISSN 0374-0676


         LIGHT CURVES OF DD Com AND TY UMa


    DD Com is an eclipsing binary of W UMa type. It has
been discovered by Hoffmeister (1964). A photographic light
curve has been published by Meinunger and Wenzel (1968). The
object has been observed on April 12, April 13, May 13, 1980
and February 11 and February 13, 1981 with the double beam
photometer at the 1.06m telescope of Hoher List Observatory.
Comparison star has been a 13th magnitude star 11mm left and
13mm above DD Com in the finding chart by Hoffmeister.
    The star showed minima at                               

JD hel.2444342.3845   Ep.24379.0   O-C -0.001d
       2444373.48        24494.5        0.00
       2444647.6750      25513.0       +0.010
       2444649.6925      25520.5       +0.008

The previously known light elements by Meinunger and Wenzel
can be slightly modified:
    JD hel. min. I = 2437779.410 + 0.2692061d E
    Light curves from the B and V measurements are shown
in Figs. 1 and 2. Not only the minima differ well in brightness, 
but also the first maximum is considerably brighter
than the second maximum. These asymmetries have decreased
between 1980 and 1981, however. It is concluded that DD Com
is a more active contact binary, similar to VW Cep.
    TY UMa has been discovered by Beljawsky (1933) and
was observed by several authors since then. But only very
shortly ago (Broglia and Conconi, 1981) the correct period
(0.35d) of this W UMa type eclipsing binary has been 
announced.


                        [FIGURE 1]

 Fig. 1   B light curve of DD Com. Dots: 1980 data, crosses:
          1981 data

                        [FIGURE 2]

             Fig. 2   V light curve of DD Com

                        [FIGURE 3]

             Fig. 3   B light curve of TY UMa

                        [FIGURE 4]

             Fig. 4   V light curve of TY UMa


    Observations of TY UMa could be obtained on February
13, 1981. BD+56d1572 served as comparison star. The observing 
instrument was again the 1.06m telescope of Hoher List
Observatory with its double beam photometer. The following
minima times have been determined:
     JD hel. 2444649.389     min.II
             2444649.564     min. I
Although both minima are 7 minutes early with respect to the
new light elements by Broglia and Conconi, a period change
since 1967 cannot be derived from this result yet. Figures 3
and 4 show the light curve of TY UMa in B and V. Especially
the V curve shows minima with constant intervals. So this is
another W UMa system with complete eclipses.
     Fourier coefficients for the light outside the eclipses 
(phases 0.16...0.34, 0.66...0.84) have been calculated:
     lB = 0.9031 + 0.0157 cos Theta - 0.0920 cos 2Theta
             - 0.0017 sin Theta - 0.0158 sin 2Theta         
     lV = 0.8729 + 0.0283 cos Theta - 0.1059 cos 2Theta
             + 0.0115 sin Theta - 0.0094 sin 2Theta
There are a positive cos Theta term and a larger sin 2Theta term.
They are in contradiction to a light curve free of complications. 
A detailed analysis should be postponed until reliably 
undistorted light curves of TY UMa are available.





                       M. HOFFMANN
                   Observatorium Hoher List
                   5568 Daun / Eifel, BRD





References:
Beljawsky, S., 1933, Variable Stars 4, 196
Broglia, P., Conconi, P., 1981, Inf. Bull. Variable Stars No. 1949 [BIBCODE 1981IBVS.1949....1B ]
Hoffmeister, C., 1964, Astron. Nachr. 288, 49 [BIBCODE 1964AN....288...49H ]
Meinunger, L., Wenzel, W., 1968, Veroff. Sternw. Sonneberg
           7, H. 4, 389 [BIBCODE 1968VeSon...7..385M ]