COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1514

                                 Konkoly Observatory
                                 Budapest
                                 1978 December 15



         POSSIBLE ECLIPSES OF BETA CAPRICORNI


     Beta Capricorni (HR7776, V = 3.07, B8V+K0 II-III,
alpha=20h15m24s, delta=-15d06' (1900)) is a triple system with a late
B star and unseen companion of period 8.68 days orbiting a late
type giant in 1374 days (Sanford 1939). Recently Evans and
Fekel* have derived a visual orbit for the long period system
by combining occultation, speckle, and spectroscopic observations. 
With the speckle observation excluded, the derived long
period orbital inclination is 90d. The best compromise with the
inclusion of the lone speckle point is an inclination of 84d.
From occultation observations the limb darkened angular diameter
of the K0 II-III star is 3 arc milliseconds. The minimum separations 
of the components of the long period orbit on the sky are
of the same order with the exact values depending on the true
value of the inclination. The possibility of eclipses, perhaps
only grazing or coronal, arises and Table I gives the predictions
for i = 84d.

                    Table I
           Predicted Eclipse Circumstances
      ----------------------------------------------
      Eclipsed components    Date    rho     Theta
                                  (arc ms) (degrees)
      ----------------------------------------------
      short period pair 1979.Mar 30  6.5      122.8
      K0 II-III         1981 Aug 20  3.0      302.8
      ----------------------------------------------

The former event should best be observed at short wavelengths
(lambda < 4200 A). Complications may arise because of the duplicity
of the visual secondary, B8V star, which should have an orbital
angular diameter of 0.7 arc milliseconds, though in which relative 
direction this pair will be elongated at the time of the
eclipses it is impossible to say.
     From occultation observations the visual components have
equal magnitudes at about 4230A. The magnitude difference
Deltam = m_B8 - m_K0 in Stromgren b = 1.1 and in y = 1.8.
     We suggest that photometric observers, particularly those
in the southern hemisphere, should search for eclipses. The
first possible eclipse occurs early in the observing season
for beta Cap and will be difficult for northern observers.
     The solution of Evans and Fekel has position angles 
decreasing with time. Radick has made an independent solution
which is closely similar to this in which he finds an inclination 
of 89d +- 6d using the spectroscopic, occultation and
speckle data and 89d +- 1.4d if the single speckle observation
is omitted. Both give a very elongated orbit with only small
changes in position angle but he prefers a solution in which
position angles increase with time. Of course if the inclination 
is exactly 90d the two solutions coalesce and the eclipses
should be the more striking.




                        DAVID S. EVANS
                        Department of Astronomy
                        University of Texas at Austin
                        Austin, Texas 78712

                        FRANCIS C. FEKEL
                        Department of Astronomy
                        University of Texas at Austin
                        Austin, Texas 78712

                        RICHARD RADICK
                        Department of Astronomy
                        University of Illinois
                        Urbana, Illinois 61801




Reference:

* Evans, D.S. and Fekel, F.C., in press, Astrophysical Journal 1979 [BIBCODE 1979ApJ...228..497E ]