MILESTONES 2010
1.- The 11-year activity cycle of the Sun is a consequence of a dynamo process occurring beneath its surface. We analysed photometric data obtained by the CoRoT space mission, showing solar‐like oscillations in the star HD49933, for signatures of stellar magnetic activity. Asteroseismic measurements of global changes in the oscillation frequencies and mode amplitudes reveal a modulation of at least 120 days, with the minimum frequency shift corresponding to maximum amplitude as in the Sun. These observations are evidence of a stellar magnetic activity cycle taking place beneath the surface of HD49933 and provide constraints for stellar dynamo models under conditions different from those of the Sun. This work was published in Science.
Time evolution (beginning February 6, 2007) of the mode amplitude (top), the frequency shifts using two different methods (central), and a starspot proxy (bottom) built by computing the standard deviation of the light curve. All of them are computed using 30 -day long subseries shifted every 15 days (50% overlapping).
2. - We have presented some of the first detailed modelling of an evolved solar-type star using the Kepler data (Metcalfe et al. 2010). Intricate comparison of stellar models has revealed stellar properties, such as radius, and age, with a precision of 2% and 15% or the Kepler target KIC 11026764. The models clearly showed that without diffusion of He there are severe discrepancies in the data fitting, while including it leads to an excellent match to the seismic data. We are now beginning to truly test stellar models using asteroseismic data.
An echelle diagram (frequency versus frequency modulo the characteristic frequency spacing) showing the seismic data in black and white in the background, and the frequencies of the two best stellar models (blue and red) that clearly match the observational data. The excellent match between the models and the data are what allows us to determine the radius to a 2% precision and the age to 15% precision.
3. - Discovery of the planet CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a ‘temperate’ photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn. The global analysis, the photometric follow-up and the discovery publication in the journal Nature was led by our group. Its publication in March 2010 generated an enormous interest in media world-wide since CoRoT-9b has been the first undoubtable planet with characteristics very similar a planet in our Solar System.