Open AccessA non‐local thermodynamic equilibrium spherical line‐blanketed stellar atmosphere model of the early B giant β CMa
Author(s) -
Aufdenberg J. P.,
Hauschildt P. H.,
Baron E.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02140.x
Subject(s) - physics , astrophysics , hydrostatic equilibrium , atmosphere (unit) , extreme ultraviolet , extreme ultraviolet lithography , stellar atmosphere , line (geometry) , atmospheric model , thermodynamic equilibrium , astronomy , stars , geometry , thermodynamics , laser , mathematics , meteorology , optics
The observed multiwavelength spectrum of the B1II‐‐III star β CMa is successfully reproduced, including the extreme ultraviolet (EUV) continuum observed by Extreme Ultraviolet Explorer (EUVE), with a non‐local thermodynamic equilibrium fully line‐blanketed spherical hydrostatic model atmosphere. The available spectrophotometry of β CMa from 500 Å to 25 μ m is best fitted with model parameters T eff = 24000 K, log g = 3.5 and an angular diameter of θ LD = 0.565 mas. We find that a neutral interstellar hydrogen column of N (H 0 ) ≃ 2 × 10 18 cm ‐2 provides the best agreement between the model EUV flux and that observed by EUVE. We use model atmosphere fits together with Hipparcos distances to calculate radii, luminosities and ionizing fluxes for β CMa and α Vir. An investigation of spherical and plane‐parallel models shows that the Lyman continuum predictions are quite sensitive to model geometry and surface gravity between effective temperatures 18 000 and 33 000 K. This result provides an explanation for the reported excesses between the observed EUV fluxes from β CMa and ε CMa and plane‐parallel model atmosphere predictions.