Determine the validity domain of the analytic near-critical disc approximation

Determine the domain of validity of the analytic, steady-state accretion-disc model for near-critical stellar rotation across different stellar masses, accretion rates, and radiative regimes.

Background

The disc prescription is derived by neglecting the term proportional to the difference between the squared angular velocity and the squared Keplerian angular velocity. This approximation is intended for stars at or only slightly above critical rotation, but the paper does not establish whether it remains reliable across the broader range of stellar masses, accretion rates, and radiative conditions relevant to binary evolution.

References

Although this approximation is supported by existing numerical studies and by order-of-magnitude checks, its domain of validity across stellar masses, accretion rates, and radiative regimes remains to be established.

— Disc-mediated angular momentum transport resolves the mass-gain problem in rotating binaries  (2609.30230 - Ljung et al., 24 Sep 2026) in Section 4.4, Current modelling challenges and next steps

We note that the implementation for this is rudimentary and further investigation is needed to determine whether this disc model could also be used to model the behaviour of Be stars, what other mechanisms need to be accounted for, and what timescales and magnitudes would be needed to reproduce the observed lifespans of Be-star discs.

— Disc-mediated angular momentum transport resolves the mass-gain problem in rotating binaries  (2609.30230 - Ljung et al., 24 Sep 2026) in Section 2.1, Implementing the disc model in MESA