2003/10/07 by Luciana Bianchi, Ralph Bohlin, Philip Massey
Physics and Astronomy · #Astronomical spectroscopy #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Line (geometry) #Population #Solar mass #Spectral line #Stars #Stellar, planetary, and galactic studies #Ultraviolet #Ultraviolet astronomy #Variable star #astro-ph
paper · pdf · doi:10.1086/380485
published as Astrophys.J. 601 (2004) 228-241 · 7 figures (some in color). ApJ, in press (tentatively V.601 Jan.20 2004)
arxiv created 2003/10/07 · openalex publication_date 2004/01/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We present Hubble Space Telescope /STIS Ultraviolet spectra of the six known Ofpe/WN9 stars ("slash stars") in M33. These stars were selected for showing the characteristics of the Ofpe/WN9 class from previous optical ground-based spectroscopy. The UV spectra are rich in wind lines whose strength and terminal velocity vary greatly across our target sample. We analyze the STIS spectra with non-LTE, line-blanketed, spherical models with hydrodynamics, computed with the WM-BASIC code. We find C to be underabundant and N overabundant with respect to the solar values, with a ratio (by mass) of C/N between 0.02 and 0.9 across the sample. Some stars show very conspicuous wind lines (P Cygni profiles), while two stars have extremely weak winds. The mass-loss rates thus vary greatly across the sample. The mass-loss rates of the hottest stars are lower than typical values of WNL stars but higher than expected for normal Population I massive stars. There is indication that the mass-loss rates may be variable in time. The C/N ratio and the other physical parameters derived by the spectral modeling ( T eff , L bol , mass) are consistent with evolutionary calculations for objects with moderately high initial masses (≈30-50 M ☉ ), evolving toward the WNL stage through an enhanced mass-loss phase.