* Astronomy

Title: The CoRoT satellite in flight : description and performance
Authors: M. Auvergne, P. Bodin, L. Boisnard, J.-T Buey, S. Chaintreuil, CoRoT team

CoRoT is a space telescope dedicated to stellar seismology and the search for extrasolar planets. The mission is led by CNES in association with French laboratories and has a large international participation: the European Space Agency (ESA), Austria, Belgium and Germany contribute to the payload, and Spain and Brazil contribute to the ground segment. Development of the spacecraft, which is based on a PROTEUS low earth orbit recurrent platform, commenced in October 2000 and the satellite was launched on December 27th 2006.
The instrument and platform characteristics prior to launch have been described in ESA publication (SP-1306) . In the present paper we detail the behaviour in flight, based on raw and corrected data. Five runs have been completed since January 2007. The data used here are essentially those acquired during the commissioning phase and from a long run which lasted 146 days, these enable us to give a complete overview of the instrument and platform behaviour for all environmental conditions. The ground based data processing is not described in detail, the most important method being published elsewhere. It is shown that the performance specifications are easily satisfied when the environmental conditions are favourable. Most of the perturbations, and consequently data corrections, are related to Low Earth Orbit (LEO) perturbations: high energy particles inside the South Atlantic Anomaly (SAA), eclipses and temperature variations, and line of sight fluctuations due to the attitude control system. Stray light due to the reflected light from the earth, which is controlled by the telescope and baffle design, appears to be negligible.

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CoRoT: 300 days in orbits.
The CoRoT satellite celebrated its 300 days in orbit, since its launch from the Baïkonour cosmodrome on December 27, 2006. The satellite has just completed its first long sequence of observation (150 days) towards the galactic centre and was turned over towards the anti-centre, in order to turn its back to Sun on October 15. After the operations, it started its second long sequence of observation on October 23. This one should continue until next March.
Since the beginning of its mission, CoRoT observed 3 carefully selected areas of the sky:

* an area in the direction of the constellation of Monoceros (Unicorn) for 60 days,
* followed by a short period (26 days) and a long period (150 days) of pointings in the opposed direction, towards the constellation of Serpens Cauda (snakes tail).

CoRoT obtains "light curves", i.e. it measured the light emitted by many stars with an unequalled precision and duration. During each series of observations, more than 12 000 lightcurves were obtained, with practically uninterrupted data.


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This is an example for illustration. The data covers a 120 days period of uninterrupted observation.
Credit CNRS

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Title: The CoRoT primary target HD 52265: models and seismic tests
Authors: M. Soriano, S. Vauclair, C. Vauclair, M. Laymand

HD 52265 is the only known exoplanet-host star selected as a main target for the seismology programme of the CoRoT satellite. As such, it will be observed continuously during five months, which is of particular interest in the framework of planetary systems studies. This star was misclassified as a giant in the Bright Star Catalogue, while it is more probably on the main-sequence or at the beginning of the subgiant branch. We performed an extensive analysis of this star, showing how asteroseismology may lead to a precise determination of its external parameters and internal structure. We first reviewed the observational constraints on the metallicity, the gravity and the effective temperature derived from the spectroscopic observations of HD 52265. We also derived its luminosity using the Hipparcos parallax. We computed the evolutionary tracks for models of various metallicities which cross the relevant observational error boxes in the gravity-effective temperature plane. We selected eight different stellar models which satisfy the observational constraints, computed their p-modes frequencies and analysed specific seismic tests. The possible models for HD 52265, which satisfy the constraints derived from the spectroscopic observations, are different in both their external and internal parameters. They lie either on the main sequence or at the beginning of the subgiant branch. The differences in the models lead to quite different properties of their oscillation frequencies. We give evidences of an interesting specific behaviour of these frequencies in case of helium-rich cores: the ''small separations'' may become negative and give constraints on the size of the core. We expect that the observations of this star by the CoRoT satellite wi ll allow choosing between these possible models.

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The Corot space telescope started its first observing run, on 3 February 2007
After analysis and characterization of the first images of the exoplanet channel, the Corot instrument was switched to the scientific observing mode for a 2-month period of time, until 2 April.
Saturating magnitude, focus and chromatic dispersion, line of sight modelling : all the parameters are nominal or compliant with adjustment precision.
Three days of operations have been devoted to generate and check with care the set of aperture masks uploaded to calculate on board the light curves of the 12 000 stars selected.
These light curves will be subsequently corrected from the instrument noises, and be distributed to the scientific community as level-1 products.
It will take several weeks to accurately isolate these noises and optimise the correction algorithms. The Corot labs are already at work....

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