The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class

By R. Hainich, U. Rühling, H. Todt, L. Oskinova, A. Liermann, G. Gräfener, C. Foellmi, O. Schnurr, W. Hamann. 2014

135 citations recorded by the source corpus.

Context. Massive stars, although being important building blocks of galaxies, are still not fully understood. This especially holds true for Wolf-Rayet (WR) stars with their strong mass loss, whose spectral analysis requires adequate model atmospheres. Aims. Following our comprehensive studies of the WR stars in the Milky Way, we now present spectroscopic analyses of almost all known WN stars in the LMC. Methods. For the quantitative analysis of the wind-dominated emission-line spectra, we employ the Potsdam Wolf-Rayet (PoWR) model atmosphere code. By fitting synthetic spectra to the observed spectral energy distribution and the available spectra (ultraviolet and optical), we obtain the physical properties of 107 stars. Results. We present the fundamental stellar and wind parameters for an almost complete sample of WN stars in the LMC. Among those stars that are putatively single, two different groups can be clearly distinguished. While 12% of our sample are more luminous than 10(6) L-circle dot and contain a significant amount of hydrogen, 88% of the WN stars, with little or no hydrogen, populate the luminosity range between log (L/L-circle dot) = 5.3 ... 5.8. Conclusions. While the few extremely luminous stars (log (L/L-circle dot) > 6), if indeed single stars, descended directly from the main sequence at very high initial masses, the bulk of WN stars have gone through the red-supergiant phase. According to their luminosities in the range of log (L/L-circle dot) = 5.3 ... 5.8, these stars originate from initial masses between 20 and 40 M-circle dot. This mass range is similar to the one found in the Galaxy, i.e. the expected metallicity dependence of the evolution is not seen. Current stellar evolution tracks, even when accounting for rotationally induced mixing, still partly fail to reproduce the observed ranges of luminosities and initial masses. Moreover, stellar radii are generally larger and effective temperatures correspondingly lower than predicted from stellar evolution models, probably due to subphotospheric inflation.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/78ae81620adf9228e03b06785c6a3682d7e175e4

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In Astronomy and Astrophysics

1. Michela Mapelli
2. Selma de Mink
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4. N. Giacobbo
5. Mario Spera
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In Instrumentation

1. Michela Mapelli
2. Selma de Mink
3. S. Charlot
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7. Julia Gutkin
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Citations in the corpus

• A new route towards merging massive black holes (2016, background): “The discovery of very massive stars (Crowther et al. 2010; Hainich et al. 2014) in the R136 region of the Large Magellanic Cloud with masses of up to 300 M , however, suggests that BH+BH binaries may form with significantly more massive components, thus enabling LIGO to detect the merger of such…”
• The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of He II λ1640 in young star clusters (2016, background): “…favour the lower luminosities (log L/L ) = 6.0 – 6.1) inferred by Doran et al. (2013) for R140a2 (WN5+O), Mk 49 (WN6) and BAT9996 (WN8) over those by Hainich et al. (2014), who obtained significantly higher values by assuming the WR dominated the continuum flux (R140a2) or on the basis of high…”
• 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 .”
• PARSEC evolutionary tracks of massive stars up to 350 M ☉ at metallicities 0.0001 ≤ Z ≤ 0.04 (2015, methodology): “To reproduce their spectra we make use of the most recent library of WR models computed by the Potsdam group (PoWR) (Gräfener, Koesterke & Hamann 2002; Hamann & Gräfener 2003, 2004; Sander, Hamann & Todt 2012; Hamann, Gräfener & Liermann 2006; Hainich et al. 2014).”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, unknown): “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).”