October 28, 2011

COROT and asteroseismology

Who does remember that CoRoT (Convection, Rotation & planetary Transits) was, at first, an asteroseismology mission? When the proposition was firstly submitted to CNES, during the symposium on scientific forecasting in Saint-Malo (in French), France, in 1993, the first exoplanets were not even discovered yet... The November issue of the magazine Pour La Science reminds the advances in stellar physics made by CoRoT and its American counterpart Kepler.
Oscillation d'une étoile. Crédits : CNES.
Oscillation of a star - credit: CNES

The knowledge about our star, the Sun, is now remarkable: mass, age, composition, physical structure, pressure and temperature profiles, rotation speed profile depending on latitude, magnetic field, ...
It is the result of almost 40 years observing the Sun, in particular the luminosity oscillations, from the ground and the space (more than 10 years with SOHO for example).
Fortified by this experience, the astronomers had the idea of applying the helioseismology technique to other stars.

Indeed, we do know since the beginning of the 20th century that some variable stars have vibration patterns. But we had to wait until 1999 to indisputably discover the first sunlike oscillations in another star.

Those variations are generally very low and the observations, only from the ground at the time, experienced corresponding limitations: atmospheric fluctuations, limited duration which make the long-period phenomena undetectable...

Nevertheless, when CoRoT was launched in late 2006, oscillations were detected in various stars from the ground. Promising results were separately obtained by the Canadian micro-satellite MOST (Microgravity and Stellar Oscillations), launched in 2003. However, the physical interpretation is still delicate because of the too low signal-to-noise value and the too short duration of the observations. The uncertainty over the age of most stars of the principal sequence is still between 30 and 50% for example.

The data from CoRoT and then from Kepler (since 2009) are stirring up the discipline. CoRoT provides light curses of hundreds bright stars with a photometric accuracy in the millionth and thousands more in the ten thousandths, for continuous durations which can reach 180 days. The stellar physics thus soared!



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