ATMOSPHERIC PARAMETERS AND EVOLUTIONARY CP STARS. I.21 COM FROM THE OLD COMAE BERENICES CLUSTER

Abstract

On the basis of Hipparcos observations and complex observations carried outat the Shamakhy Astrophysical Observatory named after N. Tusi of the National Academy of Sciences of Azerbaijan, the main parameters of the atmosphere and the evolutionary status of the magnetic CP star 21 Com from the old Comae Berenices cluster have been determined.Almost all atmospheric parameters are determined taking into account the peculiarity effect - the presence of large chemical anomalies and a strong magnetic field (Be≈1000 G). By comparing the phase curves of the magnetic field (Be), brightness (V), and equivalent widths (Wλ) of the Sr, Cr, and Eu lines, which are the main peculiar elements of the star, we determined the phases (0.95) of the maximum peculiar (P) and normal (0.45) area (N) on the surface of the star.When constructing the phase curves, we used observational materials obtained at ShAO with the use of data taken from previously published works.
To determine the absolute magnitude (Mv = 0.565) and the evolutionary status of the 21 Com star, the parallax value (π) was taken from the Hipparcos observations. It was found that it is located closer to the upper boundary (TAMS) of the MS band, where old pro-evolved magnetic CP stars are located (17 Com A, HD144897, HD177765, HD 204411, etc.
The paper discusses the question of when (or at what stage of evolution) a magnetic star acquired its anomalous chemical composition and other peculiar features (a decrease in the rotation rate and balmer jumps, a strong magnetic
field, etc.)