Description
(Text)
The study of stellar oscillations allows one to constrain the structure and dynamics of stellar interiors to a precision that cannot be achieved with other methods. This dissertation focuses on the measurements of the parameters (frequencies, amplitudes, linewidths, and rotational splitting) of the global modes of solarlike oscillations observed in the Sun and in the Sun-like star HD 52265. The thesis is organized in three main parts: (i) an implementation and validation of a global fit of stellar oscillation power spectra using solar observations, (ii) an application of this method to original 4-month-long CoRoT observations of the planet-hosting, solar-like star HD 52265, and (iii) an extension of the fitting method to time series with gaps. The main results concern HD 52265: the mode frequencies of the radial, dipole and quadrupole modes are measured with the highest precision achieved so far for a solar-type star and, for the first time, the effect of rotation on oscillationsin a solar-type star is measured unambiguously. Furthermore, the seismic constraint on the inclination angle of the stellar rotation axis allows us to estimate the absolute mass of the companion. Accordingly the seismic analysis strongly suggests that the companion is a planet and not a brown dwarf.
(Extract)
Helio- and asteroseismology are tools to investigate the interior structure and the evolution of the Sun and distant stars. Many stars of various types and evolutionary stages undergo global oscillations, which can be observed at the stellar surface in brightness or velocity. These oscillations, in particular their frequencies, contain precious information on stellar interiors, e.g. the sound speed. () The theory of stellar structure is a well-established branch in astrophysics (). Until only recently, tests of the theory of stellar structure and evolution relied mostly on the study of stellar clusters where stars are assumed to have the same age and chemical composition (). However, helio- and asteroseismology make possible the study of the structure of isolated stars and offer independent methods to test and refine the theory of stellar evolution. The confrontation of the measured oscillation frequencies and those calculated from models provide stringent constraints on the input physics of the models.
