Determine evolutionary state (RGB vs core He-burning) for ambiguous giant components

Ascertain whether the stellar components in the eclipsing binary systems Gaia DR3 3157581134781556480 (J0656), 5966976692576953216 (J1705), 1969468871480562560 (J2107), and 2002164086682203904 (J2236) are first-ascent red giant branch stars or core helium-burning stars, given that their measured dynamical masses and radii are each consistent with both evolutionary phases according to MIST evolutionary tracks.

Background

The authors construct age posteriors for each component of the eight detached eclipsing binaries by comparing their precise dynamical masses and radii to MIST evolutionary tracks. For several stars, the measured mass–radius pairs are consistent with either first-ascent red giant branch (RGB) or core helium-burning evolutionary phases, producing bimodal age posteriors.

Within the sample, the systems J0656, J1705, J2107, and J2236 have one or both components whose radii are compatible with either phase, implying genuine evolutionary-state ambiguity from mass–radius constraints alone. The authors note that, absent additional diagnostics, the two possibilities carry equal prior likelihood in their analysis.

References

For stars where the measured mass and radius could be consistent with either the first ascent up the red giant branch (RGB) or the core He-burning sequence, there are two possible stellar ages. Although the relative amplitudes of the corresponding peaks in the age posteriors differ, we do not know a priori whether a given star is a first ascent RGB star or a core He-burning star, and both have equal probability.

— Precise and Accurate Mass and Radius Measurements of Fifteen Galactic Red Giants in Detached Eclipsing Binaries  (2409.02983 - Rowan et al., 2024) in Section 6: Comparisons to Evolutionary Tracks