A NON-LTE ANALYSIS OF THE HOT SUBDWARF O STAR BD+28 degrees 4211. I. THE UV SPECTRUM

作者：Latour M^*; Fontaine G; Chayer P; Brassard P

来源：Astrophysical Journal, 2013, 773(2): 84.

DOI：10.1088/0004-637X/773/2/84

• stars: abundances
• stars: atmospheres
• stars: fundamental parameters
• stars: individual (BD+28 degrees 4211)
• subdwarfs

We present a detailed analysis of the UV spectrum of the calibration star BD+28 degrees 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 degrees 4211 to a value of T-eff = 82,000 +/- 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2(-0.1)(+0.3). Assuming that the Hipparcos measurement for BD+28 degrees 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 degrees 4211 is significantly less than the canonical value of 0.5M(circle dot) for a representative post-extended horizontal branch star.

• 出版日期2013-8-20