COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                         Number 2535

                                             Konkoly Observatory
                                             Budapest
                                             15 June 1984

                                             HU ISSN 0374-0676


            IRVBU OBSERVATIONS OF W URSAE MAJORIS

  Observations of W Ursae Majoris, on March 5-6, 1984, with the Kitt Peak
Automated Filter Photometer, on the no. 20.9 meter telescope, resulted in
15925 IRVBU observations in a single observing session. The time of midprimary
minimum was determined by finding the midpoints of chords connecting equal
values of the light level. The lower part of the light curve was symmetric
in all spectral bands. It will ultimately be possible to determine an improved 
time of minimum with the aid of light synthesis modelling. The heliocentric
midprimary time was JD 2445765.7385. The O-C residual from the ephemeris of
Hamzaoglu et al. (I.B.V.S. No. 2102) is -0.0025d. Total phase was covered
by approximately 90 observations in each spectral band. To within observational
error, primary minimum is of constant brightness, in contrast to secondary
minimum.
  There was a detectable O'Connell Effect, in the sense that the maximum
following primary minimum (Max I) was higher than the preceding one. The
magnitude difference of the two maxima, as a function of spectral band, was
as follows:

Spectral band                Max. II - Max. I

  I                               .019
  R                               .013
  V                               .010
  B                               .021
  U                               .023

  Secondary minimum was asymmetric in the sense that egress phase light
levels were below ingress phase levels, for equal displacements from
midsecondary minimum, adopted as 1/2 period from midprimary. Annular phase
of secondary minimum was not at a constant light level, but was 0.03
magnitudes brighter at second contact than third.
 A detailed description of the light curves will appear in a separate
publication.


                ALBERT P. LINNELL*

             Dept. of Physics and Astronomy
          Michigan State Univ., E. Lansing, Mich.
*
 Visiting Astronomer, Kitt Peak National Observatory, which is operated by
the Association of Universities for Research in Astronomy, Inc., under
contract with the National Science Foundation.