Core-Envelope Coupling in Intermediate-Mass Core-Helium Burning Stars

Abstract

Stars between two and three solar masses rotate rapidly on the main sequence, and the detection of slow core and surface rotation in the core-helium burning phase for these stars places strong constraints on their angular momentum transport and loss. From a detailed asteroseismic study of the mixed-dipole mode pattern in a carefully selected, representative sample of stars, we find that slow core rotation rates in the range reported by prior studies are a general phenomenon and not a selection effect. We show that the core rotation rates of these stars decline strongly with decreasing surface gravity during the core He-burning phase. We argue that this is a model-independent indication of significant rapid angular momentum transport between the cores and envelopes of these stars. We see a significant range in core rotation rates at all surface gravities, with little evidence for a convergence towards a uniform value. We demonstrate using evolutionary models that measured surface rotation periods are a biased tracer of the true surface rotation distribution, and argue for using stellar models for interpreting the contrast between core and surface rotation rates. The core rotation rates we measure do not have a strong mass or metallicity dependence. We argue that the emerging data strongly favors a model where angular momentum transport is much more efficient during the core He burning phase than in the shell burning phases which precede and follow it.

16 pages, 14 figures, Accepted for publication in ApJ

References in corpus (16)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• Slowing the Spins of Stellar Cores
• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• Target Selection for the SDSS-IV APOGEE-2 Survey
• Asteroseismic measurement of surface-to-core rotation in a main sequence A star, KIC 11145123
• The APOGEE red-clump catalog: Precise distances, velocities, and high-resolution elemental abundances over a large area of the Milky Way's disk
• Mixed modes in red giants: a window on stellar evolution
• The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
• Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry
• Impact on asteroseismic analyses of regular gaps in Kepler data
• Surface rotation of Kepler red giant stars
• Period spacings of $\gamma$ Doradus pulsators in the \textit{Kepler} field: Rossby and gravity modes in 82 stars
• Rapid Rotation of Low-Mass Red Giants Using APOKASC: A Measure of Interaction Rates on the Post-main-sequence
• Low-frequency variability in massive stars: Core generation or surface phenomenon?
• M Dwarf rotation from the $K2$ young clusters to the field. I. A Mass-Rotation Correlation at 10 Myr
• Constraining transport of angular momentum in stars: Combining asteroseismic observations of core helium burning stars and white dwarfs

Cited by in corpus (1)

• Asteroseismology of evolved stars to constrain the internal transport of angular momentum. III. Using the rotation rates of intermediate-mass stars to test the Fuller-formalism