Title: Granulation in red giants: observations by the kepler mission and three-dimensional convection simulations
Authors: Mathur, S ×
Hekker, S
Trampedach, R
Ballot, J
Kallinger, Thomas
Buzasi, D
Garcia, R. A
Huber, D
Jimenez, A
Mosser, B
Bedding, T. R
Elsworth, Y
Regulo, C
Stello, D
Chaplin, W. J
De Ridder, Joris
Hale, S. J
Kinemuchi, K
Kjeldsen, H
Mullally, F
Thompson, S. E #
Issue Date: Nov-2011
Publisher: University of Chicago Press for the American Astronomical Society
Series Title: Astrophysical Journal vol:741 issue:2 pages:-
Article number: 119
Abstract: The granulation pattern that we observe on the surface of the Sun is due to hot plasma rising to the photosphere where it cools down and descends back into the interior at the edges of granules. This is the visible manifestation of convection taking place in the outer part of the solar convection zone. Because red giants have deeper convection zones than the Sun, we cannot a priori assume that their granulation is a scaled version of solar granulation. Until now, neither observations nor one-dimensional analytical convection models could put constraints on granulation in red giants. With asteroseismology, this study can now be performed. We analyze similar to 1000 red giants that have been observed by Kepler during 13 months. We fit the power spectra with Harvey-like profiles to retrieve the characteristics of the granulation (timescale tau(gran) and power P-gran). We search for a correlation between these parameters and the global acoustic-mode parameter (the position of maximum power, v(max)) as well as with stellar parameters (mass, radius, surface gravity (log g), and effective temperature (T-eff)). We show that tau(eff) alpha v(max)(-0.89) and P-gran alpha v(max)(-1.90) which is consistent with the theoretical predictions. We find that the granulation timescales of stars that belong to the red clump have similar values while the timescales of stars in the red giant branch are spread in a wider range. Finally, we show that realistic three-dimensional simulations of the surface convection in stars, spanning the (T-eff, log g) range of our sample of red giants, match the Kepler observations well in terms of trends.
ISSN: 0004-637X
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Institute of Astronomy
× corresponding author
# (joint) last author

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