Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006msu..conf..108l&link_type=abstract
Del Toro I., J.C. et al., eds. The many scales in the universe. JENAM 2004 astrophysics reviews. Springer, 2006, p. 108-118
Astronomy and Astrophysics
Astrophysics
Stars: Atmospheres, Stars: Early-Type, Stars: Fundamental Parameters, Infrared: Stars
Scientific paper
A considerable fraction of the massive stars of our galaxy is obscured by dust. Dust extinction is preventing us from using powerful criteria, developed at UV and optical wavelength ranges, to infer physical properties of hot stars. At wavelengths longwards of about 5 microns, emission from warm dust is typically dominating the spectra. It is therefore crucial to develop diagnostic tools in the near-infrared window in order to understand the nature and evolution of hot stars surrounded by dust, as it is the case, for instance, during the early stages of their lives in giant molecular clouds. To characterize the physical parameters of these hidden massive stars, and find clues about their formation processes, we developed spectroscopic diagnostics tools based on the near-infrared wavelength range. Using a grid of 30 model atmospheres computed with CMFGEN, we find that the helium lines present in the J-, H- and K-band can be used for spectral typing of hot stars. Also the Brackett alpha line located in the L-band appears to be a good tracer of the wind density. Concerning stars that only show emission lines in the near-infrared part of their spectra, we propose a hydrogen line flux diagram to probe whether the circumstellar material is distributed in a disk or in a wind. The application of some of these diagnostics to NGC2024/IRS2 (one of the targets of our UCHII survey campaign) combined with a carefull investigation of its spectral energy distribution shows that this young massive star is very likely surrounded by a gaseous disk. Whether this disk is the signature of a remnant accretion disk is however still under debate.
Bik Arjan
de Koter Alex
Kaper Lex
Lenorzer Annique
Mokiem M. R.
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