= Algol mass-ratio stability limit
{c}
{title2=$q_{\rm crit}\simeq2/3$}
A simplified conservative model with a fully convective donor gives long-lived stable <Roche-lobe overflow> only for donor-to-accretor mass ratio $q<2/3$. This follows from the <Roche-lobe radius response exponent> and the donor's adiabatic <stellar radius response exponent> $-1/3$. The boundary is model-dependent; radiative donors, evolved core structure and mass or angular-momentum loss change it. https://arxiv.org/abs/1008.2620[Van Rensbergen and collaborators' Algol population study] includes reported Algol mass ratios above $0.7$ and discusses observational uncertainties.
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