1201.3762 (W. A. Dziembowski)
W. A. Dziembowski
Lots of information on solar-like oscillations in red giants has been
obtained thanks to observations with CoRoT and Kepler space telescopes. Data on
dipolar modes appear most interesting. We study properties of dipolar
oscillations in luminous red giants to explain mechanism of mode trapping in
the convective envelope and to assess what may be learned from the new data.
Equations for adiabatic oscillations are solved by numerical integration down
to the bottom of convective envelope, where the boundary condition is applied.
The condition is based on asymptotic decomposition of the fourth order system
into components describing a running wave and a uniform shift of radiative
core. If the luminosity of a red giant is sufficiently high, for instance at M
= 2 Msun greater than about 100 Lsun, the dipolar modes become effectively
trapped in the acoustic cavity, which covers the outer part of convective
envelope. Energy loss caused by gravity wave emission at the envelope base is a
secondary or negligible source of damping. Frequencies are insensitive to
structure of the deep interior.
View original:
http://arxiv.org/abs/1201.3762
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