Red-giant seismic properties analyzed with CoRoT^*

B. Mosser¹, K. Belkacem^2,1, M.-J. Goupil¹, A. Miglio^2**, T. Morel², C. Barban¹, F. Baudin³, S. Hekker^4,5, R. Samadi¹, J. De Ridder⁵, W. Weiss⁶, M. Auvergne¹ and A. Baglin¹

¹ LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon cedex, France e-mail: benoit.mosser@obspm.fr
² Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
³ Institut d'Astrophysique Spatiale, UMR 8617, Université Paris XI, Bâtiment 121, 91405 Orsay Cedex, France
⁴ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁵ Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁶ Institut für Astronomie (IfA), Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria

Received: 11 January 2010
Accepted: 1 April 2010

Abstract

Context. The CoRoT 5-month long observation runs provide us with the opportunity to analyze a large variety of red-giant stars and derive their fundamental parameters from their asteroseismic properties.

Aims. We perform an analysis of more than 4600 CoRoT light curves to extract as much information as possible. We take into account the characteristics of both the star sample and the method to ensure that our asteroseismic results are as unbiased as possible. We also study and compare the properties of red giants in two opposite regions of the Galaxy.

Methods. We analyze the time series using the envelope autocorrelation function to extract precise asteroseismic parameters with reliable error bars. We examine first the mean wide frequency separation of solar-like oscillations and the frequency of the maximum seismic amplitude, then the parameters of the excess power envelope. With the additional information of the effective temperature, we derive the stellar mass and radius.

Results. We identify more than 1800 red giants among the 4600 light curves and obtain accurate distributions of the stellar parameters for about 930 targets. We are able to reliably measure the mass and radius of several hundred red giants. We derive precise information about the stellar population distribution and the red clump. By comparing the stars observed in two different fields, we find that the stellar asteroseismic properties are globally similar, but that the characteristics are different for red-clump stars.

Conclusions. This study demonstrates the efficiency of statistical asteroseismology: validating scaling relations allows us to infer fundamental stellar parameters, derive precise information about red-giant evolution and interior structure, analyze and compare stellar populations from different fields.