Has a star enough energy to excite the thousand of modes observed with CoRoT?

Abstract

The recent analyses of the light curves provided by CoRoT have revealed pulsation spectra of unprecedented richness and precision-in particular, thousands of pulsating modes and a clear distribution of amplitudes with frequency. In the community, some scientists have started doubting the validity of the classical tools to analyze these very accurate light curves. This work provides the asteroseismic community with answers to this question showing that (1) it is physically possible for a star to excite at a time and with the observed amplitudes such a large number of modes; and (2) that the kinetic energy accumulated in all those modes does not destroy the equilibrium of the star. Consequently, mathematical tools presently applied to the analyses of light curves can a priori be trusted. This conclusion is even more important now, when a large amount of space data coming from Kepler is currently being analyzed. The power spectrum of different stellar cases and the non-adiabatic code GraCo have been used to estimate the upper limit of the energy per second required to excite all the observed modes and their total kinetic energy. A necessary previous step for this study is to infer the relative radial pulsational amplitude from the observed photometric amplitude, scaling our linear pulsational solutions to absolute values. The derived upper limits for the required pulsational energy were compared with (1) the luminosity of the star; and (2) the gravitational energy. We found that both upper energy limits are orders of magnitude smaller. © 2010. The American Astronomical Society. All rights reserved.