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Journal Article

Constraining the rotation profile in a low-luminosity subgiant with a surface rotation measurement


Bellinger,  Earl P.
Stellar Evolution, Stellar Astrophysics, MPI for Astrophysics, Max Planck Society;

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Wilson, T. A., Casey, A. R., Mandel, I., Ball, W. H., Bellinger, E. P., & Davies, G. (2023). Constraining the rotation profile in a low-luminosity subgiant with a surface rotation measurement. Monthly Notices of the Royal Astronomical Society, 521(3), 4122-4130. doi:10.1093/mnras/stad771.

Cite as: https://hdl.handle.net/21.11116/0000-000D-A76C-E
Rotationally induced mode splitting frequencies of low-luminosity subgiants suggest that angular momentum transport mechanisms are 1–2 orders of magnitude more efficient in these stars than predicted by theory. Constraints on the rotation profile of low-luminosity subgiants could be used to identify the dominant mechanism for angular momentum transport. We develop a forward model for the rotation profile given observed rotational splittings, assuming a step-like rotation profile. We identify a consistent degeneracy between the position of the profile discontinuity and the surface rotation rate. We perform mock experiments that show the discontinuity position can be better constrained with a prior on the surface rotation rate, which is informed by star spot modulations. We finally apply this approach to KIC 12508433, a well-studied low-luminosity subgiant, as an example case. With the observed surface rotation prior, we obtain a factor of 2 increase in precision of the position of strong rotation gradient. We recover the literature values of the core and surface rotation rates and find the highest support for a discontinuity in the radiative zone. Auxiliary measurements of surface rotation could substantially improve inferences on the rotation profile of low-luminosity subgiants with already available data.