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The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type StarsUsing the results of the most recent stellar atmosphere models applied to a sample of hot stars, we construct calibrations of effective temperature (T(sub eff)), and gravity (log(sub g)) with a spectral type and luminosity class for Galactic 0-type and early B-type stars. From the model results we also derive an empirical relation between the bolometric correction and T(sub eff) and log g. Using a sample of stars with known distances located in OB associations in the Galaxy and the Large Magellanic Cloud, we derive a new calibration of M(sub v) with spectral class. With these new calibrations and the stellar atmosphere models of Kurucz, we calculate the physical parameters and ionizing photon luminosities in the H(0) and He(0) continua for O and early B-type stars. We find substantial differences between our values of the Lyman- continuum luminosity and those reported in the literature. We also discuss the systematic discrepancy between O-type stellar masses derived from spectroscopic models and those derived from evolutionary tracks. Most likely, the cause of this 'mass discrepancy' lies primarily in the atmospheric models, which are plane parallel and hydrostatic and therefore do not account for an extended atmosphere and the velocity fields in a stellar wind. Finally, we present a new computation of the Lyman-continuum luminosity from 429 known O stars located within 2.5 kpc of the Sun. We find the total ionizing luminosity from this population ((Q(sub 0)(sup T(sub ot))) = 7.0 x 10(exp 51) photons/s) to be 47% larger than that determined using the Lyman continuum values tabulated by Panagia.
Document ID
19970023476
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1086/177020
Authors
Vacca, William D. (California Univ. Berkeley, CA United States)
Garmany, Catherine D. (Joint Inst. for Lab. Astrophysics Boulder, CO United States)
Shull, J. Michael (Joint Inst. for Lab. Astrophysics Boulder, CO United States)
Date Acquired
September 6, 2013
Publication Date
April 1, 1996
Publication Information
Publication: The Astrophysical Journal
Publisher: The American Astronomical Society
Volume: 460
Subject Category
Astrophysics
Report/Patent Number
NASA-CR-204907
NAS 1.26:204907
Report Number: NASA-CR-204907
Report Number: NAS 1.26:204907
Accession Number
97N23804
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: HF-1026.01-91A
CONTRACT_GRANT: NAGw-766
CONTRACT_GRANT: NSF AST-90-15420
Distribution Limits
Public
Copyright
Public Use Permitted.

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