COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 1022

                                 Konkoly Observatory
                                 Budapest
                                 1975 July 23

        MINIMA OF THE ECLIPSING VARIABLE U SAGITTAE


Three heliocentric times of minimum light of the eclipsing variable 
U Sagittae have been observed in the ubvy photometric system
in the years 1972-1973. BD+19d3976 (7.9, A0) was employed as the 
comparison star. The observed epochs of minimum light were obtained by
"folding" the photometric observations on the descending branch onto
the observations of the ascending branch of the light curve. The observations 
normally covered about half the light curve of primary minimum.
(i.e., halfway between first and second contact to halfway between
third and fourth contact).


The following table lists the observed minima:
------------------------------------------------------
Minima (hel.)              Minima (hel.)
      vby                        u           T_u-T_vby
------------------------------------------------------
JD 2441514.8172            JD 2441514.8179   +0.0007
      1896.8270                  1896.8274   +0.0009
      2207.8444                  2207.8447   +0.0003
------------------------------------------------------


Column one lists the average minima observed in the violet, blue, and
yellow filters (vby). In all these minima the times of minimum determined 
from observations in the three colours were in good agreement.
A typical residual is +-0d0001. The light minima observed in the ultraviolet 
(u), however, were always found to occur later (column two).
The differences between the time of the observed minimum in the ultraviolet 
(Tu) and the mean time observed in the other three colours (T_vby)
are given in the last column. The average difference, 0.0005d, corresponds 
to a delay of about 93 seconds. Although this time delay  is
small, we are confident that it is real because the c_1 index(c_1=(u-v)-(b-v),
which involves the u observations, exhibits a different behaviour at
second contact compared to third contact. This difference is not 
observed in the m_1 index (m_1=(v-b) -(b-v)) which does not include the u
magnitude in its definition. There appears to be more ultraviolet
light on the descending branch of the light curve than on the ascending 
branch at comparable phases (as determined from the observed time
of minimum from the visual, blue, and violet observations).


Department of Physics and Astronomy
Brigham Young University                     D.H. McNAMARA
                                             KENT A. FELTZ, JR.