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Astron. Astrophys. 347, 932-936 (1999)

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1. Introduction

IM Pegasi (HD 216489) is a long-period (24[FORMULA]6) single-line spectroscopic binary classified as an RS CVn type star by Hall (1976). It appears to have a circular orbit and almost synchronized rotation. The spotted K2 II-III primary shows significant light curve variations with the maximum amplitude in the V band of 0[FORMULA]3 (Strassmeier et al. 1997). IM Peg also shows rotational modulation of the Ca II infrared triplet, H[FORMULA], and Mg II h&k emission (Huenemoerder et al. 1990, Dempsey et al. 1993, 1996). From a single spectropolarimetric measurement, the magnetic field was clearly detected on the star by Donati et al. (1997).

The present paper is the first part of our study of the star. Here, we present our observations from 1996 and 1997 and determine new orbital elements and stellar parameters with better accuracy than those previously obtained. These new parameters are used in our subsequent papers where we study the spot distribution on the stellar surface with the surface imaging technique and chromospheric activity of the star.

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© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999