COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 1128

                                 Konkoly Observatory
                                 Budapest
                                 1976 April 26


    RECENT PHOTOELECTRIC OBSERVATIONS OF UX URSAE MAJORIS



   Eclipses of the nova-like variable UX Ursae Majoris have
been observed since its discovery (Beliavski 1933). From visual
observations Zverev and Kukarkin (1937) established that the
system had the relatively short period of 4h43m. Since then a
number of observers including Krzeminski and Walker (1963),
Mandel (1965), Nather and Robinson (1974) and Africano and
Wilson (1976) have pointed out that the observed time of minimum 
varies with respect to the computed time in a cyclic way
with a period of about 29 years.
   At least three mechanisms have been invoked to explain
this phenomenon: mass transfer or the presence of an unseen
third companion (Nather and Robinson 1974); apsidal motion
(Africano and Wilson 1976). As the latter have pointed out,
however, more observations are needed to determine how exactly
the variation repeats. Such are given here.
   Three times of minima were recently determined from 
photoelectric observations made in blue light with the #2, 
90-centimeter telescope at Kitt Peak and are presented in Table I.

                  Table I

              Observations
     JD_hel Minimum        O-C
      2440000+            (day)
  
      2804.8971          -0.0010
      2806.8638          -0.0010
      2807.8471          -0.0011

   The residuals, second column, have been computed from
Mandel's (1965) ephemeris for the times of eclipse. The phase
corresponding to the observed times, again from a relation
given by Mandel, is 0.73.
   Because of cycle to cycle variations in the light curves
at minimum, one would like to have at least six minima from
which to determine a mean value for the residuals. Since this
condition is not met by the present observations, likely lower
weight should be given the location of the point determined by
the present results in the O-C versus phase diagram (see, for
example, Figure 1 of Africano and Wilson 1976). However, the
point lies close to the predicted curve and is in keeping with
the suggestion that the cyclic behaviour of the residuals has
a geometric cause.




                         G.S. MUMFORD
                        Tufts University
                        Medford, Ma. USA


References:
Africano, J., and Wilson, J. 1976, Pub. A. S. P. 88, 8 [BIBCODE 1976PASP...88....8A ]
Beliavsky, S. 1933, N. N. V. S. 4, 196
Krzeminski, W., and Walker, M. F. 1963, Ap. J. 138, 146 [BIBCODE 1963ApJ...138..146K ]
Mandel, O.E. 1965, Perem. Zvezdy 15, 474 [BIBCODE 1965PZ.....15..474M ]
Nather, R.E., and Robinson, E.L. 1974, Ap.J. 190, 637 [BIBCODE 1974ApJ...190..637N ]
Zverev, M., and Kukarkin, B. 1937, N. N. V. S. 5, 125