The Spectroscopic Hertzsprung-Russell Diagram of Hot Massive Stars in the Small Magellanic Cloud

We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature Teff and surface gravities, we find that classical Be stars appear misplaced to low Teff and high lumino...

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Bibliographic Details
Published in:The Astrophysical journal 2018-11, Vol.868 (1), p.57
Main Authors: Castro, N., Oey, M. S., Fossati, L., Langer, N.
Format: Article
Language:English
Subjects:
Astrophysics
B stars
Emission lines
galaxies: stellar content
Luminosity
Magellanic Clouds
Massive stars
Metallicity
Milky Way
Spectroscopy
stars: early-type
stars: emission-line, Be
stars: fundamental parameters
Stellar age
Stellar atmospheres
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Summary:We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature Teff and surface gravities, we find that classical Be stars appear misplaced to low Teff and high luminosity in the spectroscopic Hertzsprung-Russell diagram (sHRD). Together with the most luminous stars in our sample, the stellar masses derived from the sHRD for these objects are systematically larger than those obtained from the conventional Hertzsprung-Russell diagram. This suggests that the well-known, spectroscopic mass-discrepancy problem may be linked to the fact that both groups of stars have outer envelopes that are nearly gravitationally unbound. The non-emission-line stars in our sample mainly appear on the main sequence, allowing a first estimate of the terminal-age main sequence (TAMS) in the SMC, which matches the predicted TAMS between 12 and 40 M at SMC metallicity. We further find a large underabundance of stars above ∼25 M near the zero-age main sequence, reminiscent of such earlier findings in the Milky Way and Large Magellanic Cloud.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aae6d0