Adiabatic Mass Loss In Binary Stars. IV. Low and Intermediate Mass Helium Binary Stars

TL;DR

This paper models adiabatic mass loss in low and intermediate-mass helium binary stars, providing new stability criteria that differ from classical models and have implications for understanding various binary systems and their evolution.

Contribution

It presents detailed adiabatic mass loss models for helium stars, deriving updated critical mass ratios for binary stability that improve upon classical polytropic assumptions.

Findings

Critical mass ratio q_crit ranges from 1.0 to 2.6 on He-MS.

q_crit exceeds 10 after early He-HG, indicating increased stability.

Results inform binary evolution and population synthesis for supernovae and gravitational wave sources.

Abstract

The unstable mass transfer situation in binary systems will asymptotically cause the adiabatic expansion of the donor star and finally lead to the common envelope phase. This process could happen in helium binary systems once the helium donor star fills its Roche-lobe. We have calculated the adiabatic mass loss model of naked helium stars with a mass range of 0.35\,$M_{\odot}$ to 10\,$M_{\odot}$, and every mass sequence evolved from the He-ZAMS to the cooling track of white dwarf or carbon ignition. In consideration of the influence of stellar wind, massive helium stars are not considered in this paper. Comparing stellar radius with the evolution of the Roche-lobe under the assumption of conservative mass transfer, we give the critical mass ratio $q_{\textrm{crit}}=M_{\textrm{He}}/M_{\textrm{accretor}}$ as the binary stability criteria of low and intermediate-mass helium binary stars. On He-MS, the result shows $1.0<q_{\textrm{crit}}<2.6$, which is more unstable than the classical result of polytropic model $q_{\textrm{crit}}=3$. After early He-HG, the $q_{\textrm{crit}}$ quickly increases even larger than 10 (more stable compared with widely used result $q_{\textrm{crit}}=4$), which is dominated by the expansion of radiative envelope. Our result could be useful for these quick mass transfer binary systems such as AM CVns, UCXBs, and helium novae, and it could guide the binary population synthesis for the formation of special objects such as SNe Ia and GW sources.