Elusive hot stripped helium stars (Yungelson)

Elusive hot stripped helium stars in the Galaxy [@yungelsonElusiveHotStripped2024]

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Stripped Helium Star Properties

• nonDegenerate Matter He-cores of which retained a $\lesssim 1M_{\odot }$ hydrogen-helium envelope. This chemical abundance is formed by numerous aspects \begin{list}{-}{}
• the retreat of an H-burning convective core in MS
• Mixing!
• Mass loss during RLOF
• Stellar wind from a post RLOF remnant

\item Masses of $(1-7)M_{\odot }$ \item None have been identified \item Most are lower mass $(\gtrsim 2M_{\odot })$ \item Their formation is heavily constrained by runaway-RLOF \item Likely progenitors of both hydrogen-poor and hydrogen-rich core-collapse SNe, occurring when their CO core exceeds $\approx 1.4M_{\odot }$ \item stars with mass $\lesssim 2M_{\odot }$ with hydrogen-depleted envelopes are sdO/B-type subdwarf and stripped stars with mass $\gtrsim 7M_{\odot }$ are Wolf-Rayet stars. This gap is believed to be filled with HeS stars \item \end{list}

Case B RLO

“At solar metallicity $Z=Z_{\odot }$ this results in the formation of a system with a He white dwarf component, if the ZAMS donor mass is $\lesssim 2.5M_{\odot }$ or a hot $(\log (T_{eff}\lesssim 4.4))$ stripped helium star (HeS) component, if the donors ZAMS mass is higher and the mass-loss by its stellar wind does not prevent RLOF”