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 \({\simeq}1000\) .
