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Title: A NON-LTE ANALYSIS OF THE HOT SUBDWARF O STAR BD+28 Degree-Sign 4211. I. THE UV SPECTRUM

We present a detailed analysis of the UV spectrum of the calibration star BD+28 Degree-Sign 4211 using high-quality spectra obtained with the Hubble Space Telescope and Far-Ultraviolet Spectroscopic Explorer satellites. To this aim, we compare quantitatively the observed data with model spectra obtained from state-of-the-art non-LTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. We thus determine in a self-consistent way the abundances of 11 elements with well-defined lines in the UV, namely those of C, N, O, F, Mg, Si, P, S, Ar, Fe, and Ni. The derived abundances range from about solar to 1/10 solar. We find that the overall quality of the derived spectral fits is very satisfying. Our spectral analysis can be used to constrain rather tightly the effective temperature of BD+28 Degree-Sign 4211 to a value of T{sub eff} = 82, 000 {+-} 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2{sub -0.1}{sup +0.3}. Assuming that the Hipparcos measurement for BD+28 Degree-Sign 4211 is fully reliable and that our model atmospheres are reasonably realistic, we can reconcile our spectroscopic constraints with the available parallax measurement only if the mass of BD+28 Degree-Signmore » 4211 is significantly less than the canonical value of 0.5 M{sub Sun} for a representative post-extended horizontal branch star.« less
Authors:
; ;  [1] ;  [2]
  1. Departement de Physique, Universite de Montreal, Succ. Centre-Ville, C.P. 6128, Montreal, QC H3C 3J7 (Canada)
  2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22131026
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 773; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CALIBRATION; EXPLORER SATELLITES; FAR ULTRAVIOLET RADIATION; GRAVITATION; MASS; SPECTROSCOPY; STARS; STELLAR ATMOSPHERES; TELESCOPES; ULTRAVIOLET SPECTRA