Elusive Helium Stars in the Gap between Subdwarfs and Wolf–Rayet Stars II. Nonlinear Pulsations of Stripped Helium Stars
Year: 2025
Type: article
Abstract: It is shown for the first time that the stripped helium stars with masses (2–7) $$M_{\odot}$$ which are formed in close binary systems in the so-called case B of mass-exchange and retained low-mass hydrogen-helium envelopes, experience nonlinear radial pulsations. Pulsations are excited by the $$\kappa$$ -mechanism due to helium ionization. The region of pulsational instability extends over the Hertzsprung–Russell diagram from the red giant branch to the region of effective temperatures $$4.5\lesssim\log T_{\textrm{eff}}\lesssim 4.7$$ . Stellar luminosity variations must be observed mostly in the ultraviolet. The amplitudes of pulsations of the studied models reach $$\Delta(M_{\textrm{bol}})=0.8$$ and increase as the stellar radii $$R$$ decrease. The pulsation periods of stars with $$\log T_{\textrm{eff}}>4$$ range from 0.17 to 3.9 days and decrease with decreasing $$R$$ . The stars have substantially larger $$T_{\textrm{eff}}$$ than their companions, which could be Be stars. They are the components of relatively wide binaries with orbital periods up to several years. The number of pulsating moderate-mass stripped helium stars in the Galaxy is $${\simeq}1000$$ .
Source: Astronomy Letters
Authors: Yu. A. Fadeyev, A. G. Kuranov, L. R. Yungelson
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4412496949