Gem (75Gem = HR2973 = HD62044;
) belongs to the
class of RS CVn
stars. These stars are close binaries with usually one evolved component
(sub-giant or giant) with signatures of strong activity in one or both
components.
Gem is classified as K1III and as a single-lined
binary. These and a number of further parameters of the star are listed in
Strassmeier et al. (1993, Star No. 73).
For a RS CVn star, it has an untypically long period of 19.6 days, a
fact that might lead to some other, untypical properties
(Hatzes 1993).
The latest orbit calculations were done by Bopp & Dempsey (1989). They found a marginally eccentric orbit, but note that the orbit may be circular. They remark that there is no significant change of the orbit over the time span available to them (1902-1988).
Twenty-six new radial velocities (RVs) were obtained in 3 runs in 1993, 1994 and 1995. The SOFIN high resolution echelle spectrograph was used, yielding additional to the high resolution high S/N spectra (typically S/N > 200).
The new radial velocities
offer some
prospects: first,
they extend the time base of RVs of Gem by another 7 years; thus, they
allow for further improvement of the orbital period. They are
far more accurate than any previously published radial velocities (see below).
Thus, they are used to check the non-circularity of the orbit and to determine
accurate values for all other orbital parameters. Furthermore,
due to the high resolution and the high S/N ratio the spectra might allow for
the detection of spectral lines belonging to the secondary. Additionally, some
old RVs not used by Bopp & Dempsey are supplemented. Altogether, a new orbit
determination is worthwhile, especially as a preparation of the spectra for
surface (Doppler) imaging, where the shifts due to the orbital motion and the
line profile
distortions due to star spots need to be separated with high accuracy. Surface
images from the SOFIN spectra will be discussed in a forthcoming paper.