COMMISSION 27 OF THE I. A. U.
                   INFORMATION BULLETIN ON VARIABLE STARS
                               Number 3570

                                                         Konkoly Observatory
                                                         Budapest
                                                         8 March 1991

                                                         HU ISSN 0374 - 0676


                  1988 AND 1989 PHOTOMETRY OF UZ LIBRAE


   UZ Librae (=#102 in the catalog of Strassmeier et. al. 1988) is most likely
an FK Comae star with a 4.75 day rotational period and a low mass companion.
Bopp et al. (1984) report 1983 photometry and spectroscopy. Grewing et al.
(1989) deduce the properties of individual components of the UZ Lib system from
spectroscopic and photometric data and update both the photomeric and orbital
periods.
   We present UBV photometry of UZ Lib from May 1988 and May through
July 1989. We used the 24" telescope updated by San Diego State University at
Mt. Laguna, CA. Our comparison and check stars are BD -07d4044 and BD -08d
3998. The data are in the Johnson UBV system and in the sense star - comp. We
computed the orbital phase using Phi=2445428.88 +4.767885E after Grewing et al.
(1989).
   The DeltaV light curves (see Figures 1 and 2) for both years have a double
peaked structure indicating the existence two starspot groups. The starspot
group at phase 0.2 appears to be the larger because the minimum on the light
curve is deeper.  The DeltaV light curves show an amplitude of variability of
about 0.2 magnitudes in 1988 and 0.3 magnitudes in 1989. The minimum light
phase 0.2 is fainter in 1989 than in 1988: therefore that spot group grew
between 1988 and 1989. In addition, the fainter minimum light in 1988 indicates
that the starspots were distributed more evenly over the surface of the star in
1988 than in 1989. The large amplitude of variability combined with the changes
from 1988 to 1989 suggest that UZ Lib has a high level of chromospheric
activity and changes rapidly.
   The double peaked light curves are similar to the double peaked curves seen
for the particularly active chromosphere star, BD+61d1211 during 1981 and 1982.
For BD+61d1211, these double peaked curves represent a transition period when
one spot group was breaking up and a new spot group was forming (Heckert
1990). Continued annual light curves will tell us if these double peaked light
curves in UZ Librae also represent the transition period between two spot
groups.


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


   Little color change is seen in either DeltaU-B or in DeltaB-V (See Figure 3
and 4). While the changes are small and therefore difficult to interpret, both
indices show UZ Lib becoming more red during minimum light as one would expect
if cooler starspots cause the photometric variations.
   Ron Angione scheduled very generous amounts of time on the Mt. Laguna 24"
telescope for this work. Western Carolina University provided travel funds for
PAH through a faculty research grant and additional funds. MAH received
travel support from Sigma Xi. The Research Corporation also provided partial
support for the writing of this paper.


         PAUL A. HECKERT                     MARY ANN HICKMAN
         Western Carolina University         Agnes Scott College
         Cullowhee, NC 28723                 Decatur, GA 30030
         USA                                 USA



REFERENCES:

Bopp, B.W., Goodrich, B.D., Africano, J.L., Noah, P.V., Meredith, R.J. Palmer,
       L.H., and Quigley, R.J., 1984, Astrophys. J., 285, 202. [BIBCODE 1984ApJ...285..202B ]
Grewing, M., Bianchi, L., and Garrido, R., 1989. Astron. and Astrophys., 223, 172. [BIBCODE 1989A&A...223..172G ]
Heckert. P.A., 1990, Inf. Bull. on Var. Stars, no. 3446.
Strassmeier, K.G., Hall, D. S., Zeilik, M., Nelson, E., Eker, Z., and Fekel, F.C.,
       1988, Astron. and Astrophys. Suppl. Ser., 72, 291. [BIBCODE 1988A&AS...72..291S ]