COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2863

                                       Konkoly Observatory
                                       Budapest
                                       13 February 1986

                                       HU ISSN 0374 - 0676



          BP MUSCAE - UBV LIGHT CURVE AND EPHEMERIS


  BP Mus (CPD -71deg1392, CoD -71deg 0884) has been included in my
programme of neglected Southern eclipsing binaries in 1975. At that
time the depth of the primary minimum was not known and neither was
the existence of the secondary minimum. First reasonably successful 
observations were made in 1978 and 1979. Present results are
based on photoelectric measurements in the UBV system made with the
41 cm reflecting telescope and the 1P21 photomultiplier on Siding
Spring. Observations during 13 nights in May 1978, February 1979
and June-July 1979 are of variable quality and many measurements
had to be rejected as unreliable because of cloudiness, equipment
malfunction or full moon at the time of primary minimum.
Nevertheless, these observations of such a little known star as BP
Mus yielded the following interesting results.

1. A possible variation in the length of period since the primary
minimum occured 23 hours earlier than would be expected from the
ephemeris in the GCVS (see Kviz 1979). Individual observations in
the UBV filters are plotted in Fig. 1. using the ephemeris
T-min(HJD) = 43928.138 + 3.32046.E.

2. A secondary minimum with depth of 0.1 magnitude in V has been
detected close to the phase 0.5.

3. The brightness of the star outside minima seems to have dropped
by nearly 1 magnitude since the first Hoffmeister (1943a,b) 
observations (1936-38).

4. The flat bottom of the primary minimum seems to be distorted.
(See Fig. 2, 3, and 4). The distortion occured mainly in B and is
probably an indication of gaseous streams or a disk in the system.


Table I


Filter   16/17 Feb.1979     8/9 July 1979    Min I Min II

         a - b   BP Mus     a - b  BP Mus    

V        0.433   10.200     0.433  10.190    12.97 10.27 
B        0.570   10.525     0.568  10.491    14.23 10.54
U        1.272   10.785     1.278  10.786    15.45 10.79


                        [FIGURE 1]

 Fig.1. Light curve for BP Mus in the UBV system. Abscissae: Phase.
 Ordinates: Differential magnitudes (variable minus comparison a),
 scale is exact for B, -1.5 shift for V, +1.5 shift for U.

                        [FIGURE 2]

 Fig.2. Minimum of BP Mus in V, # 13/14 Feb. 79, + 23/24 Feb. 79,
 * 26/27 June 79, o 6/7 July 79.

                        [FIGURE 3]

 Fig.3. Minimum of BP Mus in B. Symbols as in Fig. 2. Distortion of
 the bottom is clearly visible.

                        [FIGURE 4]

 Fig.4. Minimum of BP Mus in U. Symbols as in Fig. 2.


  The measurements of BP Mus and comparison stars, a=HD111442,
sp. B9.5 V and b=HD111290., sp. B1 Ib/II were tied-in to the UBV
system by measurement of standard stars in the E and F Harvard
regions. Table I shows the differences in magnitudes between comparisons 
a and b, UBV magnitudes for BP Mus on these two nights and
the UBV magnitudes at primary and secondary minima.

The photographic magnitudes given in CGVS is 9.6 and in the 
fifth edition of the Finding List (Wood et al. 1980) it is 9.5. 
Although during minimum the equipment used was working at its
limits, the observations from 4 different nights agree reasonably
well and in B they indicate the distortion of the flat part of the
primary minimum. (Raw estimates of spectral types from colours give
A5 V and K2 III).

   Further observations of BP Mus are being carried out in other
photometric systems (UBVRI, Geneva) and some have already been
reduced. These will be published elsewhere. Individual numerical
values of the observations used in this paper may be obtained from
the author or from the archives in London (Royal Astronomical
Society), Strassbourg (Centre de Donnees Stellaires) or Odessa
(Odessa Astronomical Observatory). File numbers will be published
in the PASP.

   Observations at Siding Spring Observatory were partly supported
by the Australian Research Grant Commission which is greatly appreciated. 
I wish to thank Mr. K. J. Murray and Mrs. A. E. Harris for
their assistance with observations. I am also grateful to the
director and the staff of Mt. Stromlo and Siding Spring
Observatories for facilitating the observations.




                    ZDENEK KVIZ
                 School of Physics
             University of New South Wales
             P.O.Box 1, KENSINGTON, N.S.W.
                    AUSTRALIA





References:

Hoffmeister C. (1943a), Kleinere Veroff. Berlin-Babelsberg No. 27
               (1943b), AN 273, 88. [BIBCODE 1942AN....273...88H ]
Kviz Z. (1979), IBVS 1702.
Wood F.B. (1980), Pub. Univ. Pennsylvania, Astr. Ser.12
            (= Pub. Dpt. Astronomy, Univ. Florida 1.)


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