COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 1284

                                                         Konkoly Observatory
                                                         Budapest
                                                         1977 May 26


            BD -3d5357 AN UNUSUAL ECLIPSING BINARY

We have found that the star BD -3d5357 (alpha_1950 = 21h58m01s, 
delta_1950 = -2d59' ;
mv=9.4; type K0 in the SAO catalogue) is a unique eclipsing binary containing a
red giant (~G8 III) and what is probably a hot subdwarf. This remarkable
system was initially noted as an ultraviolet source during analysis of data
from the S2/68 sky survey experiment on the TD-1 satellite. Subsequent
photometric and spectroscopic observations made at Mount Wilson, Palomar, and
Mount Laguna observatories in 1975 and 1976 have since revealed a clearer
picture of the system.
   The hot secondary is extremely blue; the satellite ultraviolet continuum
is consistent with a 38000 K black body. The eclipses in U are 1.2m deep, yet
they are barely visible in V. The UV continuum is clearly visible on our
spectrograms. The spectrum has strong Ca II H and K in emission and a very
strong H-alpha emission. We note the presence of a very strong "reflection
effect" in the system.
    Ingress and egress take only 24 minutes although the period is 9.2 days.
The U light curve is shown in Figure 1. The heliocentric times of mid-eclipse
have been found to be

           JD_hel = 2442752.9577 + 9.207755d E
                         +-.0005  +-.000010.

   The 17 radial velocities obtained in 1975 and 1976 give a preliminary value
of K1=27+-3 km sE-1 for the G8 star, but we have not yet been able to detect
lines of secondary. Therefore, we can only state that the data are consistent
with M_sd ~0.5 M_sun, R_sd ~0.1 R_sun, M_G8 ~2M_sun, R_G8 ~6R_sun. A wider
range of masses and radii are possible but all plausible models conform to the
hot subdwarf-G subgiant model. The radius of the G star is about one-half the
Roche radius.

                          [FIGURE 1]

                 Figure 1. The U light curve.


   A brief description of the eclipses is given in Tables 1 and 2.

                   Table 1

           Light Curve Description

   Filter    Eclipse    Outside     Phase of
              Depth    Variation    Maximum

     U        1.2m       0.22m       0.53p
     B        0.4        0.33        0.55
     V        0.15       0.35        0.66


             Table 2

        Eclipse Description

Eclipse         Phase     Hours:Minutes
Portion        Fraction

Ingress/       0.00175p      00:24
Egress
Eclipse        0.0625        13:48
Duration
Totality       0.0590        13:02

   Table 3 is a summary of UBV photometry of nearby field stars obtained in
1976 at Palomar Observatory with the 20-inch (50-cm) telescope on moderately
good photometric nights. BD -3d5358, the comparison star, has a close (~20
arc-sec) companion which was excluded from the photometer diaphragm. BD
-3d5362 was the check star.

                 Table 3

            Nearby Field Stars

  Star       V       B-V      U-B    n

-3d5353     9.07   +0.42    -0.03    3
-3d5355    10.91   +0.62    +0.08    3
-3d5358    10.39   +0.64    +0.12    1
-3d5359    10.38   +0.50    +0.01    3
-3d5361     9.39   +1.29    +1.27    3
-3d5362     9.58   +1.12    +0.79    2

   A more detailed analysis of the light curve and spectroscopic orbit will be
published elsewhere.


      M.M. DWORETSKY                     H.H. LANNING

      Department of Physics and          Hale Observatories
      Astronomy                          Pasadena
      University College London          California
      London WC1E 6BT                    U.S.A.


                   P.E. ETZEL and D.J. PATENAUDE

                   Mt. Laguna Observatory-Astronomy
                   Department
                   San Diego State University
                   San Diego
                   California, U.S.A.