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Astron. Astrophys. 318, 791-796 (1997)

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1. Introduction

The RS CVn system [FORMULA] Geminorum (HD62044, HR 2973) is a well-known RS Canum Venaticorum binary system with a period of 19.605 days (Bopp & Dempsey 1989). The visible primary is a red giant of spectral type K1 III. The secondary is not observed directly and does not eclipse the primary. Photometric observations have revealed the existence of large starspots (Hall 1978; Henry et al. 1995). The distance is 55.6 pc (Hoffleit & Jaschek, 1982). The Ca II H and K emissions, UV line emission, and X-ray emission of [FORMULA] Gem show the usual manifestations of high chromospheric and coronal activity. A summary of the characteristics together with added references to the activity of [FORMULA] Gem may be found in Strassmeier et al. (1988, 1993).

[FORMULA] Gem has previously been observed in X-rays (Ariel V: Pye & McHardy 1983; HEAO 1: Walter et al. 1980; Einstein Observatory: Majer et al. 1986; EXOSAT: Singh et al. 1987; ROSAT: Dempsey et al. 1993) and found to be a copious emitter of X rays. The results of the previous observations are summarized in Table 1. The radio emission at 5 GHz appears to be around 0.7 mJy during quiescent periods (Drake et al. 1989), but varies considerably.


Table 1. Summary of results from previous observations

Previous studies of active binaries may be explained by assuming the presence of a low temperature (a few MK) component and a persistent high temperature ([FORMULA] 20 MK) component (Majer et al. 1986; Schmitt et al. 1990). Two temperatures are also apparent from analyses with continuous temperature distributions which show two more or less pronounced peaks. According to Mewe (1991), this occurs because these stars may have two loop systems. There is a system with many small loops at low temperature, together with fewer, more extended loops at high temperature. The EXOSAT Observations of [FORMULA] Gem by Singh et al. (1987) was in accordance with these findings, showing a component of 8 MK and another of 40 MK.

The present study is based on ROSAT observations of [FORMULA] Gem. It is of particular interest to explore the temperature structure of the system and the variability of the X-ray emission with time.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998