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Thierry Semaan’s thesis defense

Spectroscopic characterization and pulsational study of Be stars thanks to ground-based (VLT-GIRAFFE and X-SHOOTER) and space data ( CoRoT)
» Thursday 13 September 2012


  • Anne-Marie Hubert (GEPI - Observatoire de Paris)
  • Juan Zorec (Institut d’Astrophysique de Paris)

Be stars are early-type stars having near critical rotation. They are surrounded by an equatorial disc fed by discrete mass-loss ejections from the central star. Be stars are good laboratories to study, on one hand, the impact of rotation on pulsations and, on the other hand, the role of pulsation on the recurrent mass ejections. During this thesis we focused on faint Be stars located in the first exoplanetary fields of the CoRoT satellite. In a first step we have identified the stars presenting the Be phenomenon among all the variable stars observed by CoRoT. We have thus been able to provide a sample of forty Be stars. Thanks to ground-based spectroscopic observations at VLT with GIRAFFE and X-SHOOTER instruments we have studied the spectral properties of half of them and determined their fundamental parameters by taking into account the effects of the rapid rotation. Using the CoRot light curves we have determined the frequencies and amplitudes of the pulsations that characterize the treated stars and studied their temporal variations. We have studied attentively the newly discovered stars presenting light outbursts. Thanks to the carried spectroscopic and photometric studies we have been able to investigate the properties of pulsations according to the stellar location in the HR diagram, and could identify some common properties among the Be stars of our sample.