Paul G. Beck, Josefina Montalban, Thomas Kallinger, Joris De Ridder, Conny Aerts, Rafael A. García, Saskia Hekker, Marc-Antoine Dupret, Benoit Mosser, Patrick Eggenberger, Dennis Stello, Yvonne Elsworth, Søren Frandsen, Fabien Carrier, Michel Hillen, Michael Gruberbauer, Jørgen Christensen-Dalsgaard, Andrea Miglio, Marica Valentini, Timothy R. Bedding, Hans Kjeldsen, Forrest R. Girouard, Jennifer R. Hall, Khadeejah A. Ibrahim
When the core hydrogen is exhausted during stellar evolution, the central
region of a star contracts and the outer envelope expands and cools, giving
rise to a red giant, in which convection occupies a large fraction of the star.
Conservation of angular momentum requires that the cores of these stars rotate
faster than their envelopes, and indirect evidence supports this. Information
about the angular momentum distribution is inaccessible to direct observations,
but it can be extracted from the effect of rotation on oscillation modes that
probe the stellar interior. Here, we report the detection of non-rigid rotation
in the interiors of red-giant stars by exploiting the rotational frequency
splitting of recently detected mixed modes. We demonstrate an increasing
rotation rate from the surface of the star to the stellar core. Comparing with
theoretical stellar models, we conclude that the core must rotate at least ten
times faster than the surface. This observational result confirms the
theoretical prediction of a steep gradient in the rotation profile towards the
deep stellar interior.
View original:
http://arxiv.org/abs/1112.2825
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