A calibration of iota Pegasi system

Abstract

Recent observations provide determinations of individual masses, chemical composition and metallicity of the components of the spectroscopic and interferometric binary ιPeg (Boden et al. 1998). Using updated physics, to calibrate the system, we have computed using the stellar evolutionary code CESAM, evolutionary sequences of stellar models with the masses of ιPeg A 1.326 Msol and iota Peg B 0.819 Msol (Boden et al. loc.cit) and with different values of the mixing-length parameter α, the helium Y and the heavy element Z initial mass fraction with the constraint of the observed metallicity. Adopting effective temperatures and luminosities, as derived from observations with the bolometric corrections, and the empirical scale of temperatures of Alonso et al. (1995, 1996), we find α_A=1.46, α_B=1.36, Y=0.278, Z=0.017. The evolution time, including pre-main sequence, is found within 40 My < t_ev < 0.5Gy. The calibrated models of ιPeg. A and B are non homogeneous zero age main sequence stars with the evolutionary time t_ev=56 My. Due to the large uncertainties of their determinations, the values derived for the mixing-length parameters are smaller than the solar one but however marginally compatible with it. Our results ought to be improved as soon as a more accurate value of the magnitude difference in the V filter will be available. Detailed spectroscopic analysis for both components looks practicable, so it is urgently needed.