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1. Introduction

 

tex2html_wrap_inline1729 Gem (75Gem = HR2973 = HD62044; tex2html_wrap_inline1731) 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. tex2html_wrap_inline1733 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 tex2html_wrap_inline1737 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.


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