Last news from the CoRoT satellite |
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Last news from the CoRoT satellite
The last results from the french satellite CoRoT, in orbit for more than 550 days, have been presented at various scientific conferences held recently. On his two principal missions, search for extrasolar planets and the physics of stars (study of the internal structure of stars by seismology), the satellite has obtained data with exquisite accuracy, first discoveries for most of them, of which some examples are presented here.
The researchers from Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA ) of Paris Observatory have instigated this space mission, financed essentially by France, with the collaboration of Autria, Germany, Belgium, Brazil, Spain, the European Space Agency (ESA), and realized by the CNES (Centre National d'Etudes Spatiales).
Figure 1: White light curve of CoRoT-Exo4. The curve has been normalised by its own median (Aigrain et al 2008)
Click on the image to enlarge itCoRoT discovers a new planetary system
CoRoT uses the transit method to detect extrasolar planets, measuring the darkening of a star when a possible planet, a companion, passes "in transit" in front of it. It thus detects the planet and determines, using complementary ground observations on large telescopes, its mass and its diameter. CoRoT discovered very recently CoRoT-Exo-4b. It is a gaseous giant planet similar to Jupiter: 0.72 times less massive and 1.17 times larger in diamter. Its period of rotation around its star is 9.2 days, which is the second longer period known to date for an exoplanet discovered by transit.
Figure 2: Light curve of CoRoT-Exo4 now folded and rebinned, according to the best transit model (Aigrain et al 2008).
Click on the image to enlarge it
Thanks to observations carried out over several months without interruption, the CoRoT team was able to characterize the variations of luminosity of the host star, which was attributed to the presence of dark spots on the surface, then to deduce its period of rotation. The team thus discovered that the star, whose mass is 1.13 times that of the Sun, formed with its planet a synchronous system. This result is new because the planet presents a too small mass and a too large distance compared to its star to have this kind of synchronous effect with its star.
Figure 3: Mass-Period diagram of the 35 exoplanets known by transit, showing the special position of CoRoT-Exo4b (diamond), from Moutou et al (2008).
Click on the image to enlarge itStellar seismology
Here are some examples of results raising new interrogations:
- CoRoT discovered oscillations similar to those already observed in the Sun, in all stars similar to the Sun; which shows the relationship between the Sun and these stars. The levels of the amplitude of these oscillations challenge the community on the current theory of energy transport.
- CoRoT measured the oscillations of tens of giant stars; it thus brings a bright confirmation to first results obtained by ground-based observations and opens a new field of investigation. For the brightest stars, CoRoT was able to detect very low frequencies which will make it possible to test the structure of their internal layers.
- In many stars, as in the star host of CoRoT-exo-4b, CoRoT is able to measure the period of rotation, thus helping to reach a new stage of knowledge on their evolution.
- To date, CoRoT observed more than 50.000 stars. Automatic tools are under development to be able to analyze such a large number of light curves.
- At least 50% of these stars have temporal variations, a characteristic that CoRoT was able to distinguish, whereas until now only 10% of stars were detected to be variables. These variations are being classified using a data-processing expert system.
The CoRoT satellite (Credit CNES).
References
Transiting exoplanets from the CoRoT space mission IV: CoRoT-Exo-4b: A transiting planet in a 9.2 day synchronous orbit
S. Aigrain et al.
Astronomy & Astrophysics, in pressTransiting exoplanets from the CoRoT space mission V. CoRoT-Exo-4b: Stellar and planetary parameters
C. Moutou et al.
Astronomy & Astrophysics, in pressContacts
Annie Baglin (Observatoire de Paris, LESIA, et CNRS)
Caroline Barban (Observatoire de Paris, LESIA, et CNRS)
