The long-period RS Canum Venaticorum binary IM Pegasi. I. Orbital and stellar parameters

New high-resolution and high signal-to-noise ratio spectroscopic observations carried out in 1996-1997 are analysed. A total of 85 new high quality radial velocity measurements are used for determining the new orbital parameters: T_conj=HJD2450342.883+24.64880E, e=0.0, gamma =-14.09 {km s(-1) }, K₁=34.39 {km s(-1) }. A model atmosphere analysis of the averaged spectrum of the star has yielded a self-consistent set of fundamental parameters of the primary component: {T_eff}=4450 K, {log g=2.4, [M/H]=0.0, {xi_t }=1.6 {km s(-1) }, {v sini=26.5 {km s(-1) }. The primary is found to be a typical K2 III giant with the mass of about 1.5 M_⊙ which has undergone the first convective mixing on the Red Giant Branch ([C/H]=-0.32, [N/H]=0.30, C/N=1.15). The unspotted V magnitude of the star of 5fm 55 is estimated from the observed variations of the TiO band and quasi-simultaneous photometry. Combining all parameters, the radius and inclination of the primary as well as a probable spectral class of the secondary are estimated. based on observations collected at the 2.6\,m telescope of the Crimean Astrophysical Observatory, Ukraine and the Nordic Optical Telescope (NOT), La Palma, Spain