Radial pulsations of helium stars and a model for BX CIR

• Published in: Astronomy reports 2003-01, Vol.47 (1), p.68-74
• Main Authors: Fadeev, Yu A, Novikova, M F
• Format: Article
• Language: English
• Subjects: Astrophysics; Helium; Ionization; Luminosity; Stars & galaxies
• ISSN: 1063-7729; 1562-6881
• DOI: 10.1134/1.1538497

The results of hydrodynamical calculations of radially pulsating helium stars with masses 0.5M^sub ^≤M≤0.9M^sub ^, bolometric luminosities 600L^sub ^≤5×10^sup 3^ L^sub ^, and effective temperatures 1.5×10^sup 4^ K≤T^sub eff^≤3.5×10^sup 4^ K are presented. The pulsation instability of these stars is due to the effects of ionization of iron-group elements in layers with temperatures T2×10^sup 5^ K. The calculations were carried out using opacities for the relative mass abundances of hydrogen and heavy elements X=0 and Z=0.01, 0.015, and 0.02. Approximate formulas for the pulsation constant Q over the entire range of pulsation instability of the hot helium stars in terms of the mass M, radius R, effective temperature T^sub eff^, and heavy-element abundance Z are derived. The instability of BX Cir to radial pulsations with the observed period Π=0.1066 d occurs only for a mass M≥0.55M^sub ^, effective temperature T^sub eff^≥23000 K, and heavy-element abundance Z≥0.015. The allowed mass of BX Cir is in the range 0.55M^sub ^≤M≤0.8M^sub ^, which corresponds to luminosities 800L^sub ^≤M≤1400L^sub ^ and mean radii 1.7R^sub ^R2.1R^sub ^.[PUBLICATION ABSTRACT]