2021MNRAS.503.2726H -
Mon. Not. R. Astron. Soc., 503, 2726-2732 (2021/May-2)
BAT99-9 - a WC4 Wolf-Rayet star with nitrogen emission: evidence for binary evolution?
HILLIER D.J., AADLAND E., MASSEY P. and MORRELL N.
Abstract (from CDS):
An analysis of the Large Magellanic Cloud (LMC) WC4 star BAT99-9 (HD 32125, FD 4, Brey 7, WS 3) shows that the star still contains photospheric nitrogen. Three N emission features (N V λλ1238, 1242, N IV λ1719, and N IV λλ3479-3485) are unambiguously identified in the spectrum. CMFGEN models of the star yield an N/C ratio of 0.004 ± 0.002 (by number) and a C/He ratio of 0.15–0.05+0.10. Due to the similarity of BAT99-9 to other WC4 stars, and the good fit achieved by CMFGEN to both the classic WC4 spectrum and the N lines, we argue that the N lines are intrinsic to BAT99-9. An examination of a limited set of rotating models for single-star evolution at LMC and Galactic metallicities shows that a model with a Galactic metallicity (z = 0.014) and a progenitor mass of around 50 M☉ can have an N/C ratio similar to, or larger than, what we observe for a significant fraction of its lifetime. However, the LMC models (z = 0.006) are inconsistent with the observations. Both the single and binary BPASS models predict that many WC stars can have an N/C ratio similar to, or larger than, what we observe for a significant fraction of their lifetime. While the binary models cover a wider range of luminosities and provide a somewhat better match to BAT99-9, it is not currently possible to rule out BAT99-9 being formed through single-star evolution, given the uncertainties in mass-loss rates, and the treatment of convection and mixing processes.
Abstract Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society
Journal keyword(s):
stars: early-type - stars: evolution - stars: individual: (BAT99-9 (HD 32125, FD 4, Brey 7, WS 3), BAT99-8, BAT99-11, BAT99-52) - stars: Wolf-Rayet
Simbad objects:
12
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