A Space-Based Probe of Stellar Interiors

FCOMP-01-0124-FEDER-009292 & PTDC/CTE-AST/098754/2008

Principal investigator
Margarida S. Cunha

The ultimate goal of the present project is to make a major contribution to the understanding of stellar structure and evolution. To that end we will study stellar oscillations in low- and intermediate-mass stars, at different evolutionary stages, spanning from pre-main sequence to early post-main sequence. These will include both classical pulsators, and solar-like pulsators (e.g. Cunha et al, 2007). The studies will be centered primarily on targets of the on-going french-led space mission CoRoT and of the NASA mission Kepler, that will be launched in March 2009. The quality and statistical relevance of the data to be acquired by these satellites are expected to change drastically the deepness of our understanding of stellar evolution. The access to these data is guaranteed by the active participation of the team in both missions. In particular two team members are Co-Is of the mission CoRoT, one is Co-I of the mission Kepler, and the whole team participates in the Kepler Asteroseismic Science Consortium (KASC). Given the skills of its members, we argue that our team is in a position to have a leading role in some of the major developments expected in this field of research.

Our attention will be focused on the understanding of particular aspects of the physics of stellar interiors considered of primary importance for the correct modeling of stars. These include the study of mixing and segregation processes, such as convection, overshooting, diffusion and double-diffusive processes (semiconvection and thermohaline diffusion), and rotational induced mixing. Moreover, we will consider some of the implications that planets may have on stellar evolution, providing a link between stellar and planetary physics. Our strategy will consist on addressing some of the most important issues that require to be investigated, from the moment the data on a star is acquired to the moment the final inference on the physics takes place. The underlying philosophy is that the optimal scientific outcome depends on our ability to optimise each step involved in that process. With this strategy we will optimize also the efficiency of the team, which has proven strong observational and theoretical expertise.

We propose to organise our work in three different packages. The first of these comprises issues related to the acquisition of seismic data and their analysis, and will include all steps from the observed light curves to the extraction of mode amplitudes, frequencies, and regular frequency patterns, such as the large and small separations. Moreover it will include the acquisition and analysis of complementary non-seismic data on the seismic targets. Particular emphasis will be given to the development of new methodologies for data analysis, guided by specific challenges posed by space-based and ground-based data, as well as by the need to quantify the uncertainties on the parameters extracted from the data. The second package will comprise aspects related to the modelling of stars and their pulsations, and the development of new methodologies for seismic inference. The former will be focused on the inclusion, in stellar evolution and pulsation codes, of formulations of all aspects of the physics to be studied, while the latter will focus on the implementation of new strategies for confrontation between the data and the models, and on the development of diagnostic tools aimed at isolating the signatures on the data of particular regions of stellar interiors. The third package will comprise the confrontation between the outputs of the data analysis and the models and inference tools. From that confrontation we will derive a set of parameters for the best model of each star, typically the mass, initial hydrogen and helium abundances, mixing length and overshooting parameters, stellar age, and, in the case of Ap stars, will put constraints to the topology and magnitude of the magnetic field. Moreover, we expect to estimate the size of convective cores of stars slightly more massive than the sun and characterise the sound speed profile at the borders of the core directly from the seismic data. We will also test details of the physics characterising the borders of convective regions and regions of steep chemical gradients, formulations for rotational-induced mixing, and formulations of the coupling between convection and pulsation.

Asteroseismology is a young and very fast growing field of research. While this project deals with the study of a particular set of targets, it is important to note that the tests that these targets will provide on our stellar evolution tools, and on the formulations of particular physical processes, will impact on our future ability to model stars in general. This is even more true, as for the first time in asteroseismology short history, we will be in a position to study statistically relevant sets of pulsating stars.

Project members in CAUP:
- Ahmed Grigahcene
- Antonio García Hernández
- Isa Brandão
- Joana Sousa
- Margarida Cunha
- Mário João Monteiro
- Michael Bazot
- Sérgio Sousa
- Tiago Campante

Funding institution
Fundação para a Ciência e a Tecnologia

Start: 15 February 2010
End: 14 February 2013

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