Granulation in Red Giants: Observations by the Kepler Mission and Three-dimensional Convection Simulations
- Author(s)
- S. Mathur, S. Hekker, R. Trampedach, J. Ballot, T. Kallinger, D. Buzasi, R. A. García, D. Huber, A. Jiménez, B. Mosser, T. R. Bedding, Y. Elsworth, C. Régulo, D. Stello, W. J. Chaplin, J. De Ridder, S. J. Hale, K. Kinemuchi, H. Kjeldsen, F. Mullally, S. E. Thompson
- 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 thanthe Sun, we cannot a priori assume that their granulation is a scaled version of solar granulation. Until now, neither observations norone-dimensional analytical convection models could put constraints on granulation in red giants. With asteroseismology, this study can now beperformed. We analyze ~1000 red giants that have been observed by Keplerduring 13 months. We fit the power spectra with Harvey-like profiles to retrieve the characteristics of the granulation (timescale τgran and power P gran). We search for acorrelation between these parameters and the global acoustic-modeparameter (the position of maximum power, νmax) as well as with stellar parameters (mass, radius, surface gravity (log g), and effective temperature (T eff)). We show that τeff ~νmax^-0.89 and Pgran ~ νmax^-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 realisticthree-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.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- National Center for Atmospheric Research (NCAR), University of Amsterdam (UvA), University of Birmingham, University of Colorado, Boulder, Institut de Recherche en Astrophysique et Planétologie (IRAP), University of Toulouse, Katholieke Universiteit Leuven, Eureka Scientific Inc., Université Paris VII - Paris-Diderot, The University of Sydney, University of La Laguna, Institute of Astrophysics of the Canary Islands, Université de recherche Paris Sciences et Lettres, National Aeronautics & Space Administration (NASA), Aarhus University
- Journal
- The Astrophysical Journal
- Volume
- 741
- Pages
- 119
- ISSN
- 0004-637X
- DOI
- https://doi.org/10.1088/0004-637X/741/2/119
- Publication date
- 11-2011
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103004 Astrophysics
- Keywords
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/granulation-in-red-giants-observations-by-the-kepler-mission-and-threedimensional-convection-simulations(c55dbd01-6c0e-47ab-b236-5667fd1e9edd).html