The latest scientific results of CoRoT 28/07/2008
The latest scientific results of CoRoT
CoRoT has now been for more than 575 days orbiting around the Earth. The satellite, the instrument and the ground segment perform very well. Five observations have been already completed. The sixth and current observation which started on April 14th will end in September, after almost 150 days of fixed pointing. In autumn, the programme will continue with two shorter sessions of approximately 25 days each. The latest scientific results are shortly presented below both on the Exoplanet and Seismology programmes.
CoRoT finds transiting planet in synchronous orbit
The most recent discovery of the CoRoT exoplanet programme was just presented during the last astronomy conference at St-Andrews (Scotland). CoRoT-Exo-4b is a Jupiter-like planet (0.72 Jupiter masses, 1.17 Jupiter radii) ; the discovery is important as it was found that the star host rotates synchronously with the planet's orbit and also that the planet's orbit is one of the longest period of transiting* planet ever found yet.
Thanks to CoRoT's continuous coverage over several months, the scientific team was able to track variations in the host star's brightness as dark spots on its surface rotate in and out of view, and deduce its rotation period. They found that the star (1.16 Solar masses), is rotating synchronously with the planet's orbit; this is somewhat surprising as the planet is thought to be too low mass and too distant from its star to have had much effect on its rotation. It is not known yet if the system formed this way (about 1 billion years ago) or if the synchronization happened later.
The planet's orbit (9.2 days) is one of the longest period of transiting planets found yet; CoRoT-Exo-4b occupies a previously empty region on the mass-period relation for transiting planets; According to Dr. C. Moutou from LAM laboratory, it is an important discovery ; by populating this region of the mass-period diagram, CoRoT will likely allow to go further in the study of the interaction between the giant planets and the stars and in the understanding of the mechanisms that drive the contraction and formation of the planets.
Transiting planets*: a transit is a tiny dips in a star's flux when a planet passes in front of it; it is used by CoRoT to detect extrasolar planets and measure, in combination with complementary ground-based observations, their radii and masses. Because it is free of the perturbing effect of the Earth's atmosphere, the satellite is expected to detect planets down to 1.5 Earth radii.
The ground-based follow-up of the CoRoT detection was done with the spectrographs SOPHIE at the Observatoire de Haute Provence (France), HARPS at La Silla observatory (Chile) and UVES on the Very Large Telescope (Chile), the 1 m telescope at the Wise Observatory (Israel), the Euler telescope at La Silla, and the 3.6 m Canada-France-Hawaii telescope.
On the seismology side
In the meanwhile, the analysis of the data of the programme of seismology is speeding up. The scientists have presented the first results in several international conferences, as for instance in Phuket (Thailand), in Wroclaw (Poland) and in Liège (Belgium). The quality of the data and the newness of the results have impressed the audiences, and excitation is growing among the specialists. Some guesses about theoretical interpretations start to be discussed. Let's for instance cite:
- the discovery of oscillations in all the stars which resemble the Sun, as expected but with different amplitudes, which question the present representation of the energy exchanges;
- the clear measurement of oscillations in tens of faint giant stars comes as a wonderful confirmation of hopes motivated by the few previous detections (less than 10) established mostly from the ground and set the stage for the development of this specific field;
- for the brightest ones, CoRoT has detected very low frequency coherent pulsations, which will allow to probe the structure of the internal layers;
- in many stars we are now able to measure the period of rotation, and try to understand their evolution. Before, only an upper limit was accessible through a measurement of a projected rotation velocity;
- the total number of stars observed reaches now more than 50 000. Automatic tools are then necessary to analyse such a large set of light curves. At least half of the stars have measurable variations. These variations are being classified, using a learning machine, and if some have an already known behavior, others look quite weird.
- Transiting exoplanets from the CoRoT space mission IV: CoRoT-Exo-4b: A transiting planet in a 9.2 day synchronous orbit : S. Aigrain, A. Collier Cameron, M. Ollivier, et al., A&A submitted
- Transiting exoplanets from the CoRoT space mission V. CoRoT-Exo-4b: Stellar and planetary parameters : C. Moutou, H. Bruntt, T. Guillot, A. Shporer, E. Guenther, et al, A&AL