COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3253

                                                    Konkoly Observatory
                                                    Budapest
                                                    21 October 1988

                                                    HU ISSN 0374 - 0676


          1987 PHOTOMETRY OF XY URSAE MAJORIS

XY UMa (= +55d1317, SAO 27143, #69 in the catalog of
Strassmeier et al., 1988) is the most active member of the
short-period RS CVn group (Budding and Zeilik, 1986). Geyer
(1980) has observed the system since 1955; he attributes its
photometric distortion wave to starspot activity on the primary
star.
   Aside from Geyer's persistent scrutiny, few complete light
curves are available to track the magnetic activity cycles of
this system. Zeilik et al.(1983) observed XY UMa in Jan-Feb
1982; Jassur (1986) in March 1979; Lorenzi and Scaltriti (1977)
present Oct-Dec 1975 Observations, but in general, their coverage
is incomplete.
   We conducted observations on 27 and 28 Feb 1987 and 29 Mar
and 2 Apr 1987 (U.T.) to complete the light curve. We used the
61-cm telescope operated by San Diego State University on Mt.
Laguna, California. The photoelectric photometer uses an EMI
6256 phototube operated at 1300 volts and cooled to -23 degC. The
photometer was fitted with an OG-515 filter for V-band. Each
observation consisted of three separate 60-second observations
through n 19 arcsec aperture. Phases were calculated from the
ephemeris given in Strassmeier et al.(1988). The comparison
star for all observations was SAO 27139 (Geyer's comparison star)
and the check star was SAO 27151. Figure 1 shows the light
curves in the instrumental V-band system, in the sense of
comparison star-variable.


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


   We analyzed the light curve by the technique of Budding and
Zeilik (1987), in which we parameterize starspot indices by
fitting a dark, circular spot to the distortion wave. We assumed
a spot temperature = 0 K (completely black), a choice that
minimizes the effective area. Figure 2 shows the observed points
(open circles) compared to the theoretical light curve (solid
line) for an unspotted system. The delta magnitudes have been
converted to relative intensity units, normalized so that the
shoulders of the light curves have a value ~1.0. Figure 3 has
the distortion wave (circles) extracted from Figure 1 and shows
the starspot fit (solid line). We assume that the primary star
is the active one. We optimized a fit with a single spot group
located at longitude 269 deg +/- #6 deg, latitude = 40 deg +/- #36
deg with a radius of 9.2 deg +/- #4.0 deg. Note the large correlated
error in the latitude, which also affects the value of the radius.
The longitude, though, is well-determined and further confirms the
notion that the active regions tend to appear at quadrature in
the short-period RS CVn systems. Budding and Zeilik (1987) find
two spots at longitude 81.4 deg +/-3.2 deg and 13.0 deg +/-0.3 deg at
a fixed latitude of 45 deg. Since 1982, the two spots have merged
(or one has disappeared). The total spotted area has also decreased
significantly.

   We thank Ron Angione for scheduling the observing time at Mt.
Laguna.


P. HECKERT                        M. ZEILIK

Dept. of Chemistry and Physics    Institute for Astrophysics
Western Carolina University       University of New Mexico
Cullowhee, N. C. 28723            Albuquerque, N. M. 87131



REFERENCES:

Budding, E. and Zeilik, M., in Cool Stars Stellar Systems and the Sun, edited by
   M. Zeilik and D. Gibson (Springer-Verlag, 1986), pp. 290-293. [BIBCODE 1986LNP...254..290B ]
Budding, E. and Zeilik, M., Ap.J., 319, 827-835 (1987). [BIBCODE 1987ApJ...319..827B ]
Geyer, E H., in Close Binary Stars: Observations and Interpretation, edited by
   M.J. Plavec, D.M. Popper, and R.K. Ulrich (Reidel, Dordrecht), pp. 423-427
   (1980). [BIBCODE 1980IAUS...88..423G ]
Jassur, D.M.Z., Astrophys. and Space Sci., 128, 369-375 (1986). [BIBCODE 1986Ap&SS.128..369J ]
Lorenzi, L. and Scaltriti, F., Acta Astronomica, 27, 273 (1977). [BIBCODE 1977AcA....27..273L ]
Strassmeier, K.G., Hall, D.S., Zeilik, M., Nelson, E., Eker, Z., Fekel, F. C.,
   Astron, Astrophys Suppl. Ser. 72, 291-345 (1988). [BIBCODE 1988A&AS...72..291S ]
Zeilik, M., Elston, R., and Henson, G., A.J., 88, 532-534 (1983). [BIBCODE 1983AJ.....88..532Z ]