Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02

摘要

Observations of giant stars indicate that the frequency of giant planets ismuch higher for intermediate-mass stars than for solar-like stars. Up to nowall known planets of giant stars orbit at relatively far distances from theirhost stars. It is not known whether intermediate-mass stars also had manyclose-in planets when they were on the main sequence, which were then engulfedwhen the star became a giant star. To understand the formation and evolution ofplanets it is therefore important to find out whether main-sequence stars ofintermediate-mass have close-in planets or not. A survey for transiting planetsof intermediate-mass stars would be ideal to solve this question, because thedetection of transiting planets is not affected by the rapid rotation of thesestars. As a first step for an efficient survey we need to identifyintermediate-mass stars in the CoRoT-fields, which can then be used as an inputlist. To compile the input list we derived the spectral types of essentiallyall O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02taken with the multi-object spectrograph AAOmega. We determined the spectraltypes by comparing the spectra with template spectra from a library. In totalwe identify 1856 A and B stars that have been observed with CoRoT. Given thenumber of planets that have been detected in these fields amongst late-typestars, we estimate that there are one to four transiting planets ofintermediate-mass stars waiting to be discovered. Our survey not only allows usto carry out a dedicated planet search programme but is also essential for anytypes of studies of the light curves of early-type stars in the CoRoT database.We also show that it would be possible to extend the survey to all fields thatCoRoT has observed using photometrically determined spectral types.