Seismology, rotation and convection with COROT – SIROCO

1 – Scientific background and objectives Our project is attached to the seismic part of the spatial mission COROT (COnvection, Rotation and planetary Transits). The launch of COROT in December 2006 has been a complete success. The duration of the mission will be a minimum of 2.5 years, including at least 5 sequences of continuous long run of 150 days each, measuring the micro-variations of the light emitted. With these observations, we will be able to detect with very high precision the many oscillation modes of stars. The asteroseismology method allows, by their analysis, to probe very precisely the physics of stellar interiors. The 3 partners of this project (some of them in the core of the scientific preparation of COROT for more than 10 years) decided to join their efforts and complementary competences to obtain the highest scientific benefits of the very precise data expected with this instrument in the forthcoming months. The core of our project is to develop new models including a more detailed physical description of the stellar interiors and the energetic of their oscillations, as well as appropriate seismic analysis tools. They will allow us to get the highest scientific return from the very precise observations of COROT during the period in which we have exclusive access to the data (from early 2007 to early 2011). 2 - Description of the project The three partners of this project are specialized in different aspects of stellar physics and asteroseismology and their contribution to the project will concern these expertises. To accomplish the different tasks of our projects, we need 3 2-year postdocs, one in each of our teams. The first group of tasks, which will be accomplished by the LESIA team, concerns the seismic interpretation of the COROT data for solar-type and intermediate-mass stars. The goal is to study the superficial convection in solar-type stars, the core convection and associated mixing in intermediate mass stars, the transport processes associated with rotation and the driving mechanisms in these stars. The second group of tasks, which will be accomplished by the GEPI team, concerns the seismic interpretation of the COROT data for massive stars. The goal is to determine the mode parameters of these COROT targets, to separate this information from their long-term and episodic variations in the case of Be stars, to study the transport processes associated with rotation and the driving mechanisms in these stars. The third group of tasks, which will be accomplished by the Toulouse team, concerns the detailed study of the physics of oscillation modes in rapidly rotating stars. These models will then be used to better interpret the observations by COROT. These three groups of tasks are highly complementary. We face a common problematic: interpret the seismic observations of COROT. A typical example of close link and transfer of competences between our teams concerns the transport processes and the role of rotation in stellar interior. Each team studies specific aspects of this problem and will benefit from the work of the others. We also plan to organize regular meetings (one for each long run of COROT observations) with the other international teams involved in COROT. The main goals are to reinforce the communication between the scientists of different teams and countries working on the seismic interpretation of the COROT targets and allow a better coordination of their work. 3 – Expected results The goal of this ANR project is first to provide tools and models and then with them to fully exploit the data of unprecedented quality obtained by COROT for all types of stars. Some of the tools available today are not adapted for such high-precision data and, in some cases, only very preliminary models exist to interpret the seismic data. Better tools and models are thus much needed for COROT to deliver a detailed picture of the interiors and transport processes of stars. This will represent a major step forward in our understanding of stars since such results currently exist only for our Sun. The outcome of our work combined with the COROT data will thus open a new area in stellar physics. We aim at providing first answers to central questions such as: - How can we describe convective envelopes and their interaction with oscillations ? - Extension of convective core: which part is due to rotation which part is due to thermal convection ? - Be stars: What is the origin of their mass loss, is it due to pulsation ? - Transport processes in radiative zones: what is the respective weight of the different processes ? - How the expected revision of stellar evolution theory impacts other fields in astrophysics ? Thanks to COROT and our project, France would then be the leader in the field of asteroseismology, both on the observational and modelling aspects.