Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit

By G. Graefener, W. Hamann. 2008

155 citations recorded by the source corpus.

The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the final fate of massive stars and their chemical yields. Its Z-dependence is discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs) and the yields from early stellar generations. However, the mechanism of formation of WR-type stellar winds is still under debate. We present the first fully self-consistent atmosphere/wind models for late-type WN stars. We investigate the mechanisms leading to their strong mass loss, and examine the dependence on stellar parameters, in particular on the metallicity Z. We identify WNL stars as very massive stars close to the Eddington limit, potentially still in the phase of central H-burning. Due to their high L/M ratios, these stars develop optically thick, radiatively driven winds. These winds show qualitatively different properties than the thin winds of OB stars. The resultant mass loss depends strongly on Z, but also on the Eddington factor, and the stellar temperature. We combine our results in a parametrized mass loss recipe for WNL stars. According to our present model computations, stars close to the Eddington limit tend to form strong WR-type winds, even at very low Z. Our models thus predict an efficient mass loss mechanism for low metallicity stars. For extremely metal-poor stars, we find that the self-enrichment with primary nitrogen can drive WR-type mass loss. These first WN stars might play an important role in the enrichment of the early ISM with freshly produced nitrogen.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/90d4418f604cfd181f216e9734e605999243fecf

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In Astronomy and Astrophysics

1. Michela Mapelli
2. N. Giacobbo
3. Mario Spera
4. G. Meynet
5. N. Langer
6. Ilya Mandel
7. D. Holz
8. S. Ekström

Citations in the corpus

• New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star-forming dwarf galaxies (2014, methodology): “More recently however, the behaviour of the mass-loss rates around this transition has been thoroughly analyzed by Gräfener & Hamann (2008) and by Vink et al. (2011).”
• TYPE Ib/c SUPERNOVAE IN BINARY SYSTEMS. I. EVOLUTION AND PROPERTIES OF THE PROGENITOR STARS (2010, result): “The most recent theoretical models of WR winds by Vink & de Koter (2005) and Gräfener & Hamann (2008) also give WR mass loss rates compatible to the Nugis & Lamers rate (cf. Figure 1 in Yoon & Langer 2005).”
• The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae (2016, background): “…metallicity stars have, during most of their evolution, winds with lower mass-loss rates (e.g. Kudritzki, Pauldrach & Puls 1987; Vink, de Koter & Lamers 2001; Krtička 2006; Mokiem et al. 2007; Gräfener & Hamann 2008) and somewhat lower terminal velocities (Leitherer et al. 1992; Krtička 2006).”
• Mass loss from hot massive stars (2008, methodology): “…the fact that the first generation(s) of massive stars start their evolutionary clock with few metals, the objects may enrich their outer atmospheres with nitrogen and carbon due to rotational mixing (Meynet et al 2006), inducing a strong line-driven wind (Vink 2006, Gräfener and Hamann 2008).”
• The cosmic merger rate of neutron stars and black holes (2018, background): “…with β = 0.85 if Γe < 2/3, β = 2.45 − 2.4 Γe if 2/3 ≤ Γe ≤ 1, and β = 0.05 if Γe ≥ 1 (where Γe is the electron-scattering Eddington ratio, i.e. the ratio between current stellar luminosity and Eddington luminosity, Vink et al. 2001; Vink & de Koter 2005; Gräfener & Hamann 2008; Chen et al. 2015).”
• COSMIC Variance in Binary Population Synthesis (2019, methodology): “Thus, we include Eddington-limited winds using the prescriptions described in Gräfener & Hamann (2008); Giacobbo et al. (2018).”
• Grids of stellar models with rotation - II. WR populations and supernovae/GRB progenitors at Z = 0.014 (2012, methodology): “The WR stars are computed with the Nugis & Lamers (2000) prescription, or the Gräfener & Hamann (2008) recipe in the restricted validity domain of this prescription.”
• Merging black hole binaries with the SEVN code (2018, background): “Massive metal-poor stars are thought to lose less mass by stellar winds than their metal-rich analogues (Vink, de Koter & Lamers 2001; Gräfener & Hamann 2008; Vink et al. 2011).”
• The cosmic merger rate of stellar black hole binaries from the Illustris simulation (2017, background): “With respect to Belczynski et al. (2010), there is one crucial update: we take into account the dependence of the mass loss Ṁ on the electron-scattering Eddington ratio Γ (Gräfener & Hamann 2008; Vink et al. 2011; Vink 2016).”
• Merging black hole binaries: the effects of progenitor's metallicity, mass-loss rate and Eddington factor (2017, methodology): “In fact, Gräfener & Hamann (2008) and Vink et al. (2011) show that the massloss rate is strongly enhanced when the star approaches the electron-scattering Eddington limit Γe.”
• Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo (2018, background): “Examples include mass loss(Vink et al. 2001; Vink & de Koter 2005; Gräfener & Hamann 2008) and supernovae(O’Connor & Ott 2011; Fryer et al. 2012; Janka 2012; Ugliano et al. 2012; Ertl et al. 2016; Sukhbold et al. 2016).”
• Fundamental properties of core-collapse Supernova and GRB progenitors: predicting the look of massive stars before death (2013, methodology): “The radiative mass-loss rates for OB stars follow the Vink et al. (2001) prescription, while for WR stars the Nugis & Lamers (2000) and Gräfener & Hamann (2008) prescriptions are employed.”
• THE EFFECTS OF STELLAR ROTATION. II. A COMPREHENSIVE SET OF STARBURST99 MODELS (2014, methodology): “ṀW−R is based on empirical values from Nugis & Lamers (2000) and Gräfener & Hamann (2008), which are already downward-corrected for inhomogeneities.”
• Wind modelling of very massive stars up to 300 solar masses (2011, methodology): “6.2) of CAK and Gr¨afener & Hamann (2008), before ending with a summary in Sect.”
• The mass spectrum of compact remnants from the parsec stellar evolution tracks (2015, methodology): “Tang et al. (2014) show that the metallicity effect can be expressed as with the coefficient α determined from a fit to the published relationships by Gr¨afener & Hamann (2008): (2 / 3 ≤ (cid:5) ≤ 1) .”
• Very massive stars, pair-instability supernovae and intermediate-mass black holes with the sevn code (2017, background): “In the last decade, the models of stellar winds underwent a major upgrade (Vink et al. 2001; Gräfener & Hamann 2008; Vink et al. 2011; Muijres et al. 2012; Vink 2016), which radically changed the landscape of massive star evolution (e.g. Paxton et al. 2013, 2015; Chen et al. 2015).”
• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, methodology): “Nevertheless, it seems that the “proper” WN stars increase their mass-loss rates while evolving towards the Eddington limit, in line with hydrodynamical models calculated by Gräfener & Hamann (2008).”