Asteroseismic measurement of core and envelope rotation rates for 2006 red-giant branch stars

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.