COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 298

                                    Konkoly Observatory
                                    Budapest
                                    1968 September 10


     OBSERVATIONS OF PRIMARY MINIMUM OF UX URSAE MAJORIS


Photoelectric observations of the short-period Algol-type eclipsing variable UX
UMa have been obtained on two nights in 1967 and eight nights in 1968 for the
purpose of deriving accurate times of primary minimum. The observations were
made using the 24-inch reflector of the Lick Observatory and a photometer
employing a 1P21 photomultiplier tube refrigerated with dry ice. All
observations were made through a blue filter composed of 2 mm Schott GG 13 plus
1 mm Schott BG 12.

The observed times of primary minimum are listed in Table 1, together with the
residuals between the observed times and those calculated from the elements
derived by Johnson, et al. (1954):

Minimum=JD_hel 2427341.2221+0.^d196671379E.

Table 1

Observed minima of UX Ursae Majoris, 1967-1968

Helioc. JD     O-C       Helioc. JD    O-C
              (day)                   (day)
2439000+                2439000+
528.94283    -0.00463   978.72946    -0.00544
529.92653    -0.00428
966.73241    -0.00554   244000+
972.82988    -0.00488   004.88711    -0.00508
975.77969    -0.00514   026.71741    -0.00531
977.74635    -0.00519   028.88097    -0.00513

Comparison of the present residuals with those obtained for earlier
observations using the same elements (see Krzeminski and Walker 1963) shows
that the period, which apparently increased from 1937 to 1953 and then
decreased from 1953 to 1962, has continued to decrease since 1962, but at a
slower rate. It appears just possible that the variation in the residuals
might be periodic with a period of about 10^4 days. Accurate observations of
the times of primary minimum of UX UMa are needed every one or two years so
that we may follow and eventually interpret the changes in period.


                              MERLE F. WALKER^*
                 Lick Observatory, University of California

References:

Johnson, E.L., Perkins, B., and Hiltner, W.A. 1954, Ap.J. Suppl., 1, 91 (No.
   4).
Krzeminski, W., and Walker, M.F. 1963, Ap.J., 138, 146.

* On leave, 1968/1969, at Cerro Tololo Inter-American Observatory, La Serena,
   Chile