A Non-LTE Analysis of the Hot Subdwarf O Star BD+28°4211. I. The UV Spectrum
Abstract
We present a detailed analysis of the UV spectrum of the calibration star BD+28°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°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°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°4211 is significantly less than the canonical value of 0.5 M ⊙ for a representative post-extended horizontal branch star.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2013
- DOI:
- 10.1088/0004-637X/773/2/84
- arXiv:
- arXiv:1306.3457
- Bibcode:
- 2013ApJ...773...84L
- Keywords:
-
- stars: abundances;
- stars: atmospheres;
- stars: fundamental parameters;
- stars: individual: BD+28°4211;
- subdwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 21 pages, including 10 online figures, accepted for publication in The Astrophysical Journal (june 12, 2013)