COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                   Number 2872

                                  Konkoly Observatory
                                  Budapest
                                  3 March 1986

                                  HU ISSN 0374 - 0676



          U CEPHEI:  AN UNUSUAL DEVELOPMENT




   The eclipsing binary U Cephei, BD+81 25, was observed on
the night of August 13, 1985 at the Stephen F. Austin State
University Observatory. The observations were made with the
46cm reflector, which uses a Starlight-1 photometer with an
uncooled EMI 9798A phototube. The observations of U Cephei
were made as part of our study of the W Serpentis star
systems, described elsewhere (Wilson, Rafert and Markworth,
1985).
   During that night, 208 observations in the natural V and
R system of the telescope/photometer combination were made,
centered approximately on mid-eclipse. Normals of these
observations, which are presented in Figures 1 and 2, were
used to determine two new timings of primary minimum. The
comparison star used was BD +81 30. The observations were
automatically recorded with our digital data acquisition
system, which uses a Commodore C-64 for photometer control,
and a Rockwell AIM-65 for telescope control. The two
computers communicate over a parallel data link in order to
synchronize their operation.
   As the eclipses of U Cephei are rather asymmetric, the
quoted timings of minimum below were calculated by fitting
the bottom of the eclipse curve (i.e., before the inflexion



points) by a parabola (Method I). As can be seen in either
of the figures, the total portion of primary minimum appears
to have a slight slope, so we also calculated timings of
minimum with the data at the bottom of the eclipse excluded
(Method II). The excluded data was centered upon the timing
of minimum found by Method I +/- 0.015 in phase. For these


                       [FIGURE 1]

 FIGURE 1. The differential V magnitudes for U Cephei in the
 sense (variable-comparison). Each point is a normal of two
 observations.


                        [FIGURE 2]

 FIGURE 2. The differential R magnitudes for U Cephei in the
 sense (variable-comparison). Each point is a normal of two
 observations.


least squares fits, the quoted error was determined by
standard error propagation techniques. For either method, we
obtain rather sizeable residuals (O-C) from the ephemeris
2438291.5330 +2.4930475 quoted by Olson, et.al. (1981).
O-C's were calculated from Method I. Numerical results are
presented in Table I.


    Because of the apparent slope to the data in the extreme
bottom of the eclipse, we also applied a linear least squares


                    Table I

                 JD (2440000+)     JD(2440000+)
       Filter      Method I         Method II      O-C
         V        6291.7430        6291.7428     0.0206
                      .0099            .0184
         R        6291.7414        6291.7541     0.0190
                      .0097            .0084

fit to just this data. Surprisingly, the slope (delta
mag/delta phase) of this portion of the light curve is 1.34
in the Visual, and 0.91 in the Red. These slopes are larger
than the error in the slopes (as determined from the errors
of the coefficients) by a factor of about 3. Alternatively,
the total portion of primary eclipse can be considered to
have both a "high" and a "low" part, although this is not so
clear in the Red. Nonetheless, in the Visual, there is a
fairly well defined drop of 0.06 magnitudes.
    This evidence suggests that U Cephei could be involved
in a high level of mass transfer, during which a gas stream
from secondary to primary, or an uneclipsed portion of a gas
disk around the primary component may have been visible
following second contact.
   This material is based upon work supported by the
National Science Foundation under Grant Number AST840-1479.


   J.B. RAFERT                        N.L. MARKWORTH
   E. SMITH

Florida Institute of Technology       Stephen F. Austin State
Department of Physics and             University
Space Sciences                        Department of Physics and
Melbourne, Florida 32901              Astronomy
USA                                   Nacogdoches, Texas 75962
                                      USA

References:

Olson, E.C., Crawford, R.C., Hall, D., Louth, H., Markworth,
    N.L., and Piirola, V., 1981, Publ. Astron. Soc. Pacific,
    93, 464. [BIBCODE 1981PASP...93..464O ]

Wilson, R.E., Rafert, J.B., and Markworth, N.L., 1985, "The
    W Serpentis Stars", Communications of the I.A.P.P.P.,
    No. 16, 1. [BIBCODE 1984IAPPP..16....1W ]