The Galactic WC stars Stellar parameters from spectral analyses indicate a new evolutionary sequence

By A. Sander, W. Hamann, H. Todt. 2012

170 citations recorded by the source corpus.

[Abridged] [...] AIMS: We aim to establish the stellar parameters and mass-loss rates of the Galactic WC stars. These data provide the empirical basis of studies of (i) the role of WC stars in the evolution of massive stars, (ii) the wind-driving mechanisms, and (iii) the feedback of WC stars as input to models of the chemical and dynamical evolution of galaxies. Methods: We analyze the nearly complete sample of un-obscured Galactic WC stars, using optical spectra as well as ultraviolet spectra when available. The observations are fitted with theoretical spectra, using the Potsdam Wolf-Rayet (PoWR) model atmosphere code. A large grid of line-blanked models has been established for the range of WC subtypes WC4 - WC8, and smaller grids for the WC9 parameter domain. Both WO stars and WN/WC transit types are also analyzed using special models. Results: Stellar and atmospheric parameters are derived for more than 50 GalacticWC and two WO stars, covering almost the whole GalacticWC population as far as the stars are single, and un-obscured in the visual. In the Hertzsprung-Russell diagram, theWC stars reside between the hydrogen and the helium zero-age main sequences, having luminosities L from 10^4.9 to 10^5.6 Lsun. The mass-loss rates scale very tightly with L^0.8. The two WO stars in our sample turn out to be outstandingly hot (\approx200 kK) and do not fit into the WC scheme. Conclusions: By comparing the empirical WC positions in the Hertzsprung-Russell diagram with evolutionary models, and from recent supernova statistics, we conclude that WC stars have evolved from initial masses between 20 solar masses and 45 Msun. In contrast to previous assumptions, it seems that WC stars in general do not descend from the most massive stars. Only the WO stars might stem from progenitors that have been initially more massive than 45 Msun.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f2038206c46e620935e39ec1c301c831e7dde566

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In Astronomy and Astrophysics

1. G. Meynet
2. S. Ekström
3. J. Eldridge
4. R. Hirschi
5. S. Smartt
6. C. Conroy
7. C. Georgy
8. Andre Maeder

Citations in the corpus

• Grids of stellar models with rotation - II. WR populations and supernovae/GRB progenitors at Z = 0.014 (2012, methodology): “The answer is likely no, since many of the low-luminosity WC stars analysed by Sander et al. (2012) have visual magnitudes well above the low r visual magnitude, which would imply detection of the progenitor by Smartt (2009).”
• Massive double compact object mergers: gravitational wave sources and r-process element production sites (2013, background): “This obviously affects the population computations that predict the number of WR single stars (Vanbeveren et al., 1998c, 2007; Sander et al., 2012).”
• Forming short-period Wolf–Rayet X-ray binaries and double black holes through stable mass transfer (2017, background): “…of masses of WR stars, either in binary systems or from their absolute luminosities have shown that, in order to show the typical WR spectral characteristics produced by a dense high-velocity stellar wind outflow, the helium stars must have a mass >∼ 10(±2) M (Crowther 2007; Sander et al. 2012).”
• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, methodology): “In Hamann et al. (2006, hereafter HGL06) we presented a comprehensive analysis of the Galactic WN stars, while the WC subtypes were studied by Sander et al. (2012).”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, background): “These are compared against observed WR stars (Crowther et al. 2002; Hamann, Gräfener, & Liermann 2006; Sander et al. 2012; Tramper et al. 2013; Hainich et al. 2014; Hainich et al. 2015; Shenar et al. 2016).”
• Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, background): “…library of line-blanketed, non-LTE, spherically expanding models of Hamann & Gräfener (2004, see also Gräfener et al. 2002; Hamann & Gräfener 2003; Hamann et al. 2006; Sander et al. 2012; Hainich et al. 2014, 2015; Todt et al. 2015),1 available at four metallicities, 0.07Z , 0.2Z , 0.5Z and Z .”
• Fundamental properties of core-collapse Supernova and GRB progenitors: predicting the look of massive stars before death (2013, methodology): “Sander et al. (2012) reached a similar conclusion by comparing their observations with the Meynet & Maeder (2003) non-rotating evolutionary tracks.”