A VLT/UVES spectroscopy study of O2 stars in the LMC
Department of Physics and Astronomy, University of Sheffield Hicks Building, Hounsfield Road, Sheffield, S3 7RH, United Kingdom
Department of Physics and Astronomy, University of Sheffield Hicks Building, Hounsfield Road, Sheffield, S3 7RH, United Kingdom
Abstract
We have analysed VLT/UVES spectra of six O2 stars within the Large Magellanic Cloud using the non-LTE atmospheric code CMFGEN. A range of physical properties was determined by employing a temperature calibration based upon NIV-NV diagnostics. Wind properties were also obtained from the Halpha line, while CNO surface abundances were supplied through various diagnostics. Our results reveal effective temperatures in excess of Teff ±50 kK in all cases. We also addressed their evolutionary status and favour a mass dependent division. For lower masses ≤100Mo, an O2 star follows the classical sequence, evolving from dwarf on to giant, through to supergiant. At higher masses, the dwarf phase may be circumvented and instead O2 stars begin their lives as giants or supergiants, evolving to the H-rich WN stage within ±1.5 Myr.