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Astron. Astrophys. 334, 863-872 (1998)

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The active RS Canum Venaticorum binary II Pegasi *

I. Stellar and orbital parameters

S.V. Berdyugina 1, 2, S. Jankov 3, I. Ilyin 1, I. Tuominen 1 and F.C. Fekel 4

1 Astronomy Division, University of Oulu, P.O. Box 333, FIN-90571 Oulu, Finland (e-mail: sveta@ukko.oulu.fi)
2 Crimean Astrophysical Observatory, P.O. Nauchny, Crimea, 334413 Ukraine
3 Universidade de São Paulo, Depto. de Astronomia, C.P. 30627, São Paulo 01051, Brazil
4 Center for Automated Space Science and Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37203, USA

Received 11 December 1997 / Accepted 5 March 1998

Abstract

A detailed model atmosphere analysis of high-resolution and high S/N CCD spectra of II Peg has yielded for the first time a self-consistent set of fundamental parameters of the primary component: [FORMULA] =4600 K, log g =3.2, [M/H]=-0.4 , [FORMULA] =2.0 km s-1. In addition, 121 new high quality radial velocity measurements 1 allowed us to determine improved orbital parameters, resulting in a new orbital ephemeris of [FORMULA] =2449582.9268+6.724333E. The position of the primary of II Peg in the HR diagram with the new parameters corresponds to a K2 IV star with mass [FORMULA] 0.8 [FORMULA]. The evolved character of the star is confirmed by the C/N ratio, which is reduced significantly relative to the solar value. The unspotted V magnitude of the star of 6 [FORMULA] 9 is estimated from the observed variations of the TiO bands and quasi-simultaneous photometry. The blend of Li I 6707 Å is suspected to vary in equivalent width due to spot modulation. The lithium abundance for the unspotted star, Li/H=1.0 [FORMULA] 0.1, is found to be consistent with other post-main sequence chromospherically active stars. Combining all parameters, the radius R  [FORMULA]  3.4 [FORMULA] and the inclination i   [FORMULA]   [FORMULA] of the primary are estimated with the assumption that its rotational axis is perpendicular to the orbital plane. The secondary is probably a M0-M3 V star with a mass of about 0.4 [FORMULA].

Key words: stars: binaries: spectroscopic – stars: fundamental parameters – stars: abundances – stars: activity – stars: individual: II Peg

* based on observations collected at the Nordic Optical Telescope (NOT), La Palma, Spain; the 2.6 m telescope of the Crimean Astrophysical Observatory, Ukraine; the 2.7 m and 2.1 m telescopes of the McDonald Observatory, USA; the coudé feed telescope of the Kitt Peak National Observatory, USA

Send offprint requests to: S.V. Berdyugina

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© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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