Query : 2017MNRAS.471..877K

2017MNRAS.471..877K - Mon. Not. R. Astron. Soc., 471, 877-890 (2017/October-2)

Quantitative spectroscopy of extreme helium stars Model atmospheres and a non-LTE abundance analysis of BD+10°2179.


Abstract (from CDS):

Extreme helium stars (EHe stars) are hydrogen-deficient supergiants of spectral type A and B. They are believed to result from mergers in double degenerate systems. In this paper, we present a detailed quantitative non-LTE spectral analysis for BD+10°2179, a prototype of this rare class of stars, using UV-Visual Echelle Spectrograph and Fiber-fed Extended Range Optical Spectrograph spectra covering the range from ∼3100 to 10 000 Å. Atmosphere model computations were improved in two ways. First, since the UV metal line blanketing has a strong impact on the temperature-density stratification, we used the ATLAS12 code. Additionally, We tested ATLAS12 against the benchmark code STERNE3, and found only small differences in the temperature and density stratifications, and good agreement with the spectral energy distributions. Secondly, 12 chemical species were treated in non-LTE. Pronounced non-LTE effects occur in individual spectral lines but, for the majority, the effects are moderate to small. The spectroscopic parameters give Teff =17 300±300 K and log g = 2.80±0.10, and an evolutionary mass of 0.55±0.05 M. The star is thus slightly hotter, more compact and less massive than found in previous studies. The kinematic properties imply a thick-disc membership, which is consistent with the metallicity [Fe/H] ≃ -1 and α-enhancement. The refined light-element abundances are consistent with the white dwarf merger scenario. We further discuss the observed helium spectrum in an appendix, detecting dipole-allowed transitions from about 150 multiplets plus the most comprehensive set of known/predicted isolated forbidden components to date. Moreover, a so far unreported series of pronounced forbidden He I components is detected in the optical-UV.

Abstract Copyright: © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal keyword(s): line: formation - stars:abundances - stars: atmospheres - stars: fundamental parameters - stars: individual: BD+10 2179 - stars: individual: BD+10 2179

Status at CDS : Large table(s) will be appraised for possible ingestion in VizieR.

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 V* DN Leo Pu* 10 38 55.2343433712 +10 03 48.486337812   9.76 9.93     Bp 141 0
2 V* BX Cir Pu* 14 01 36.4829811264 -66 09 56.163698820 11.79 12.62 12.58 12.75   OB+ 59 0
3 V* V4334 Sgr CV* 17 52 32.69352 -17 41 08.0160           F2Ia 361 0
4 LAWD 74 WD* 19 20 34.9229289504 -07 40 00.065957592 11.553 12.345 12.290 12.229 12.164 DBQA5 217 0
5 HD 188112 HS* 19 54 31.4191828536 -28 20 20.679710640   10.01 10.22     sdB 89 0

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