The active RS Canum Venaticorum binary II Pegasi. I. Stellar and orbital parameters
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: {T_eff}=4600 K, {log g=3.2, [M/H]=-0.4, {xi_t }=2.0 {km s(-1) }. In addition, 121 new high quality radial velocity measurements allowed us to determine improved orbital parameters, resulting in a new orbital ephemeris of T_conj=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 ~0.8 M_⊙. 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 6fm 9 is estimated from the observed variations of the TiO bands and quasi-simultaneous photometry. The blend of Li{ i 6707 Angstroms is suspected to vary in equivalent width due to spot modulation. The lithium abundance for the unspotted star, Li/H=1.0±m0.1, is found to be consistent with other post-main sequence chromospherically active stars. Combining all parameters, the radius R ~ 3.4 R_⊙ and the inclination i ~ 60° 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 M_⊙.
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 Table 2 is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- June 1998
- Bibcode:
- 1998A&A...334..863B
- Keywords:
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- STARS: BINARIES: SPECTROSCOPIC;
- STARS: FUNDAMENTAL PARAMETERS;
- STARS: ABUNDANCES;
- STARS: ACTIVITY;
- STARS: INDIVIDUAL: II PEG