COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2169

                                  Konkoly Observatory
                                  Budapest
                                  1982 June 23

                                  HU ISSN 0374-0676





          1982 UBVR PHOTOMETRIC OBSERVATIONS OF XY UMa



   As part of our program of photometric observations of RS CVn stars, we
have observed the short-period (0.48 day) system XY UMa (SAO 27143). The
primary star is G2-G5; the secondary K5 (Geyer, quoted by Lorenzi and Scaltriti,
1977). The observations were made in the UBVR instrumental bands on two nights
in January and February of 1982. UNM's Capilla Peak Observatory's 61-cm 
telescope employing a computer-controlled, single-channel, photon-counting photometer
with an EMR 641A phototube (cooled to -20dC) was used for all observations.
   The results of our observations are shown in Figures 1-4. The error in
any data point is +-0.01 magnitude. SAO 27139 (+54d1278) was used as the 
comparison star, and the phases were calculated using HJD=2435216.5086 + 0.478995E
(Wood, Oliver, Florkowski, Koch, 1980). Table 2 gives a phase log for the
observations.

                               [FIGURE 1]
                               [FIGURE 2]
                               [FIGURE 3]
                               [FIGURE 4]

   XY UMa has been found to exhibit large and long-term changes in its light
curve and system brightness. Geyer (1977) and Geyer and Metz (1977) attribute
the variability to starspot activity of the hotter component. Geyer's light
curves show strong asymmetries, even the disappearance of the secondary eclipse
in 1975. Our light curves are similar to the observations made by Geyer in
1976. Both primary and secondary eclipses are asymmetric with the secondary
becoming more pointed at longer wavelengths. Also, the light curve is depressed
around phase 0.25 relative to phase 0.75 by 0.04 magnitude at U, 0.03 at B, 0.02
at V, and 0.01 at R. This would indicate a distortion wave of small amplitude
with a minima at about phase 0.25.


                    Table 1

                XY UMa 1982 Phase Log
               Date     Phase
               1-31     0.04 -> 0.20
               2-20     0.12 -> 0.62



   M. ZEILIK, D. BATUSKI, R. ELSTON, G. HENSON, P. SCHMOLKE, P. SMITH

                    Capilla Peak Observatory

               Department of Physics and Astronomy

                   University of New Mexico

                  Albuquerque, New Mexico 87131

                            U.S.A.





References;

Geyer, E.H., 1977, Astrophys. and Space Sci., Vol. 48, 137. [BIBCODE 1977Ap&SS..48..137G ]
Geyer, E. H. and Metz, K., 1977, Astrophys. and Space Sci., Vol. 52, 351. [BIBCODE 1977Ap&SS..52..351G ]
Lorenzi, L. and Scaltriti, F., 1977, Acta Astron., Vol. 27, 273. [BIBCODE 1977AcA....27..273L ]
Wood, F., Oliver, J., Florkowski, D., Koch, R., 1980,Pub. of the University
   of Pennsylvania Astronomical Series, Vol. XII.