Properties and nature of Be stars
XX. Binary nature and orbital elements of
 Cas
P. Harmanec1,2,
P. Habuda3,
S. Stefl2,
P. Hadrava2,
D. Korèáková4,2,
P. Koubský2,
J. Krtièka4,2,
J. Kubát2,
P. Skoda2,
M. Slechta2,
and
M. Wolf1
1
Astronomical Institute of the Charles University,
V Holesovièkách 2, CZ-180 00 Praha 8,
Czech Republic
2
Astronomical Institute of the Academy of Sciences,
CZ-251 65 Ondrejov, Czech Republic
3
Faculty of Mathematics and Physics of the Charles University,
Ke Karlovu 3, CZ-121 16 Praha 2, Czech Republic
4
Department of Theoretical Physics and Astrophysics,
Faculty of Science, Masaryk University, CZ-611 37 Brno, Czech Republic
An analysis of accurate radial velocities (RVs) of the Be star
 Cas
from 295 Reticon spectrograms secured between October 1993 and May 2000
allowed us to prewhiten the RVs for the long-term changes
and to obtain the first orbital RV curve of this star. The orbital period
is 203.59 days and the orbit has an eccentricity of 0.26. The orbital motion
is detectable even in the published velocities, based on photographic
spectra. This implies that
Cas
is a primary component of
a spectroscopic binary. The secondary has a mass of about 1 solar mass,
appropriate for a white dwarf or a neutron star, but it could also be
a normal late-type dwarf. The ultimate solution of the dispute whether
the observed X-ray emission is associated with the secondary or with
the primary will need further dedicated studies.
Accepted by Astronomy and Astrophysics Letters
Preprints from
hec@sunstel.asu.cas.cz
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