Asteroseismic measurement of core and envelope rotation rates for 2006 red-giant branch stars
Year: 2024
Type: article
Abstract: Mixed modes of RGB stars enable us to study the internal physics from core to surface, such as differential rotation. However, envelope rotation rates have been measured for only a dozen RGB stars so far. The limited sample hinders the theoretical interpretation of angular momentum (AM) transport in post-main-sequence phases. We apply a new approach to calculate the asymptotic frequencies of mixed modes, which accounts for the near-degeneracy effects and leads to more proper measurements of envelope rotation rates. By fitting these asymptotic expressions to the observations, we obtain measurements of the properties of g modes in about 2500 stars. Among these, we measured the core and envelope rotation rates in 2006 stars, doubling the size of pre-existing catalogues. We find a bimodal distribution of the core rotation rates, implying that some stars could experience a different AM transport. We also increase the sample of stars with measured envelope rotation rates by two orders of magnitude, and find a decreasing trend between envelope rotation rates and evolution, implying that the envelopes slow down with expansion, as expected. We find that the core-to-envelope rotation ratios are of about 20 and show a large spread with evolution. Several stars show core-to-surface ratios between 1 and 2, suggesting peculiar AM transport in their progenitors. We also discovered more stars below the degeneracy sequence, providing the opportunity to study stellar mergers.
Authors: Li, Gang, Deheuvels, Sébastien, Ballot, Jérôme
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6893075136
FWCI:
Cites:
Cited by:
Related to: