This diagram is used to determine the fundamental parameters of the stars; each point being a potential target of CoRoT. The red ones are dwarf stars, the green ones are giant stars, less favourable for the search of exoplanets with the transit method.
Paris Observatory / LESIA
For the sismology program it is necessary to :
Know precisely the effective temperatures, luminosities, surface gravity values, rotation velocities, and the surface abundances of the chemical elements of all the potential target stars of the mission.
Identify the multiple and double systems
Pick out all the particularities of the stars observed (for instance a high level of magnetic activity).
Detect the presence of sources near the target stars.
The knowledge of this information requires a ground-based observation program which has three constituents : Photometry, Spectroscopy, and Imaging with all the results gathered in a database.
The transits are easier to detect around dwarf stars.
If the density of the stars is too low, the number of possible targets is too low. If it is too high, the images of the nearby stars overlap and pollute the observation.
The image here gives a representation of bright stars, potential targets of CoRoT in the region of the star HD49933, and a possible position for the detectors.
The colour of the symbol is related to the surface temperature of the star, the size, and its brightness.
Among these stars, CoRoT will only observe five per detector.