COMMISSIONS 27 AND 42 OF THE IAU
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3891

                                           Konkoly Observatory
                                           Budapest
                                           7 June 1993

                                           HU ISSN 0374 - 0676


     PRECISION UBVRI OBSERVATIONS OF THE VERY SHORT PERIOD
                 ECLIPSING BINARY BC GRUIS


As a part of our current study of very short period eclipsing binary systems,
we have obtained complete U,B,V,R,I light curves of the tenth magnitude (V)
variable, BC Gruis (S 6498 Gru).  The system was discovered by Hoffmeister
(1963) in his photographic search for variable stars in southern star fields.
Included in his paper is a finding chart for the variable.  Later, 16 times of
minimum light were published by Meinunger (1979) along with an early period
determination of P = 0.26617 d.  Gomez et al.  (1988) published a V light curve
of BC Gru, from their photoelectric observations, showing it to be a W UMa
system with rather shallow eclipses.  Also, they report that they have 15
unpublished epochs of minimum light and give an improved ephemeris, with a much
longer orbital period than Meinunger (1979).


    JD Hel. Min. I = 2447375.7828(1) + 0.30731(1)d * E.      (1)

Plewa and Kaluzny (1992) reported on their 1986 U,B,V,R,I photoelectric
observations and published U,V,I light and U-B, R-I, V-R and B-V color curves.
From their five timings of minimum light they found a period similar to that of
Gomez et al.  (1988), P = 0.30735(2) d.

The present observations of BC Gru were made on 4 - 11 August, 1991 inclusive.
The Yale 1M Ritchey-Cretien Telescope at Cerro Tololo InterAmerican Observatory
was used.  The photometry was done in the Johnson-Cousins' system with standard
U,B,V,R_c,I_c filters using the Automated Single Channel Aperture Photometer
with a dry-ice-cooled Hamamatsu R943-02 Ga-As photomultiplier tube.  The
coordinates of the check, comparison, and the variable star are given in Table
I.  About 550 observations were taken in each pass band.


                                [FIGURE 1]

 Fig. 1 - Light curves of BC Gru as defined by the individual observations.


               Table I

Star         R.A.            Dec.
             (2000)          (2000)
BC Gru       22h 44m 45.1s   -48d 09'50"
Comparison   22  44  45      -48  07 22
Check        22  45  33      -48  08 45

Four mean epochs of minimum light were determined from our observations made
during one secondary and three primary eclipses.  These were determined from an
iterative technique based on the Hertzsprung method (1928), except for the
earliest timing in B which was done by the method of bisection-of chords.  The
epochs of minimum light are given in Table II.

                      Table II

 JD HEL.
2440000+       Minimum   Cycles       (O-C)_2    (O-C)_3
    8473.7799(4)  I      -16.0        -0.0019    0.0005
    8474.7021(3)  I      -13.0        -0.0018    0.0006
    8478.6964(3)  I        0.0        -0.0031    0.0008
    8479.7726(3)  II       3.5        -0.0026    0.0003

All published timings, including those of Meinunger (1979) were introduced into
a least squares solution with visual and photoelectric epochs assigned weights
of as 0.1 and 1.0, respectively, to obtain the following ephemeris:

      JD Hel. Min. I = 2448473.782(11) + 0.3073577(7)d * E.    (2)

The O-C residuals calculated from equation (2) appear as (O-C)_2 in Table II.
Using available photoelectric epochs only, we calculated the improved
ephemeris,

       JD Hel. Min I = 2448478.7795(2) + 0.30735687(4)d * E.     (3)

Ephemeris (3) was used to calculate (O-C)_3 in Table II and to phase our
present observations.  From our ephemerides (2) and (3).  we find that the
epoch given in equation (1) is a secondary rather than a primary eclipse.
Also, it has a high O-C residual, (O-C)_3 = +0.036.

The B, V, R, and I light curves of BC Gru defined by individual observations
are presented in Figure 1 as delta m versus phase.  A very preliminary analysis
of the observations shows this system to be of W-type in very shallow physical
contact (if at all in contact) with a difference in component temperatures of
delta T ~ 400K with a large mass ratio of q ~ 0.8.  Much of the preliminary
analyses was done by Mr.  Kirk Becker as a part of his undergraduate research
project.  Further results and a complete analysis of the observations will be
published elsewhere.


                 RONALD G. SAMEC*
                 Department of Physics and Astronomy
                 Millikin University
                 Decatur, IL 62508

                 KIRK BECKER
                 J. I. Holcomb Observatory
                 Butler University
                 Indianapolis, IN 46208 USA

* Visiting Astronomer.  Cerro Tololo Inter-American Observatory.  National
Optical Astronomy Observatories, which are operated by the Association of
Universities for Research in Astronomy. Inc. under contract with the National
Science Foundation.

References:

Gomez, M., Lapasset, E., Ahumada, J., Claria, J.J., and Minniti, D. 1988, Bol.
   Asoc. Argentina Astron. 34, 119 [BIBCODE 1988BAAA...34..119G ]
Hertzsprung, E. 1928, Bull. Astron. Inst. Netherlands 4, 179 [BIBCODE 1928BAN.....4..172H ]
Hoffmeister, C. 1963, VSS 6(1). 36
Meinunger, I. 1979, VSS 9(2) 114
Plewa, T. and Kaluzny, J. 1992, AA 42, 103 [BIBCODE 1992AcA....42..103P ]