Core-Envelope Coupling in Intermediate-Mass Core-Helium Burning Stars. (arXiv:1911.01443v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tayar_J/0/1/0/all/0/1">Jamie Tayar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beck_P/0/1/0/all/0/1">Paul G. Beck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pinsonneault_M/0/1/0/all/0/1">Marc H. Pinsonneault</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garcia_R/0/1/0/all/0/1">Rafael A. García</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mathur_S/0/1/0/all/0/1">Savita Mathur</a>
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.
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.
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