COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3061

                                       Konkoly Observatory
                                       Budapest
                                       10 August 1987

                                       HU ISSN 0374 - 0676




      HD 185510: A CALCIUM-EMISSION BINARY WITH ECLIPSES OF
                   A SUBDWARF COMPANION

   HD 185510 is a K0 III-IV star with strong Ca II H and K emission
(Bidelman and MacConnell 1973). It is a light variable with a photometric
period of approximately 25 days (Henry, Murray, and Hall 1982). Radial
velocities and photometry obtained at SAAO (Balona, Lloyd Evans, and Koen:
to be published in SAAO Circulars) yield an orbital period of 20.658 days
and an improved photometric period of 25.4 days. The secondary star is a
B subdwarf (Fekel and Simon 1985), which is eclipsed at phase 0.40 in the
orbital ephemeris using T = 2,440,000.0. The eclipse of the hot star is
prominent in U - B (see Fig. 1), but is much smaller in B - V (depth of
0.02 to 0.03 mag). At these longer wavelengths the eclipse variations are
dominated by starspot activity on the primary star.


                          [FIGURE 1]

 Fig. 1. Photometry of HD 185510 from the SAAO. Zero phase
 corresponds to JD 2,440,000.0.

                          [FIGURE 2]

 Fig. 2. Low dispersion spectra of HD 185510 obtained with the
 ultraviolet cameras of IUE. The brights out-of-eclipse spectrum of the
 hot subdwarf is present in the upper curve, but there is no trace of
 this star in the lower spectrum, which was taken when the subdwarf was
 eclipsed by the primary. In both observations the Lyman-alpha line is
 contaminated by geocoronal emission and has been clipped. We identify
 the Mg II emission line in the long-wavelength region with the
 chromosphere of the late-type primary.


At far ultraviolet wavelengths the eclipse of the secondary star
appears to be total. Fig. 2 shows a recent out-of-eclipse spectrum of the
subdwarf that we obtained with the IUE satellite on JD 2,446,713.42
(corresponding to phase 0.98) and a follow-up observation made with the
same exposure time on JD 2,446,742.69 at the time of secondary eclipse.
The total eclipse of the subdwarf in the later observation is unmistakable. 
A third spectrum was kindly taken for us by Dr. Chris Shrader of
the IUE Observatory staff on JD 2,446,370.67 during ingress when the
subdwarf was not fully occulted. This observation appears to show
atmospheric eclipse effects due to the extended chromosphere and
transition region of the primary star.
  Ground-based observations of HD 185510 in the current observing
season were resumed at the SAAO in April 1987. Radial velocity
observations show no significant error in the orbital ephemeris, but an
uncertainty of several hours cannot be excluded as the semi-amplitude, K,
of the velocity curve is only 9.6 km s^1. Photometry near the time of the
eclipses of April 1-2 and April 22 showed no fading in U at 0.7627 and
0.3720 days, respectively, before the predicted dates of mid-eclipse.
Therefore, the phase of mid-eclipse may be somewhat later than 0.40. The
range of the 25-day photometric light wave in V is now 8.26 to 8.45 mag,
which is 0.05 mag brighter overall than in 1979-81. This suggests that
the spots on the K star have evolved since the earlier observations.
  Observations of HD 185510 from the SAAO are continuing. In addition,
IUE observations during the ingress and egress phases of the eclipse
predicted for 1987 October 25 are planned to study the atmospheric
structure of the K star. Additional photometry of HD 185510 from other
observatories at a range of longitude would be most valuable, as a
complete eclipse curve is needed to interpret the spectroscopic data.
observations should cover the hours before and after the photospheric
eclipse when the atmospheric eclipse will take place. Measurements at U
and B are most important for this purpose. Observations at longer
wavelengths (in V, R, and I) would also be useful for establishing the
location and geometry of the starspots on the active primary star. The
preferred local standard is HD 185587, V = 9.089, B - V = +0.182 and U - B
= -0.019, which lies 7 arcmin ESE. HD 185567, which is 8 arcmin SE of HD
185510 and is a better match in color and magnitude, may be variable
(Lloyd Evans, Koen, and Hultzer 1983).
T.L.E. wishes to thank Drummond Laing, Fred Marang, and Hartmut Winkler
for making photometric observations in 1987. T.S. and G.S. thank Chris
Shrader for assistance with the IUE observations.


L.A. BALONA            		THEODORE SIMON

T. LLOYD EVANS
                        	NASA/Goddard Space Flight Center
S A Astronomical Observatory    Code 681
P O Box 9              		Greenbelt, MD 20771
Observatory 7935       		U S A
South Africa

              GEORGE SONNEBORN

              IUE Observatory/CSC
              Goddard Space Flight Center
              Greenbelt, MD 20771
              U S A


References:

Bidelman, W.P., and MacConnell, D.J. 1973, A.J. 78, 687. [BIBCODE 1973AJ.....78..687B ]
Fekel, F.C., and Simon, T. 1985, A.J. 90, 812. [BIBCODE 1985AJ.....90..812F ]
Henry, G.W., Murray, S., and Hall, D.S. 1982, I.B.V.S. No. 2215.
Lloyd Evans, T., Koen, M.C.J., and Hultzer, A.A. 1983, SAAO Circ. 7, 82. [BIBCODE 1983SAAOC...7...82L ]