Stellar and wind properties of LMC WC4 stars A metallicity dependence for Wolf-Rayet mass-loss rates ?

By P. Crowther, L. Dessart, D. John Hillier, J. Abbott, A. Fullerton. 2002

155 citations recorded by the source corpus.

We use ultraviolet space-based (FUSE, HST) and optical/IR ground-based (2.3 m MSSSO, NTT) spectroscopy to determine the physical parameters of six WC4-type Wolf-Rayet stars in the Large Magellanic Cloud. Stellar parameters are revised significantly relative to Grafener et al. (1998) based on improved observations and more sophisticated model atmosphere codes, which account for line blanketing and clumping. We find that stellar luminosities are revised upwards by up to 0.4 dex, with surface abundances spanning a lower range of 0.1 C/He 0.35 (20-45% carbon by mass) and O/He 0.06 (10% oxygen by mass). Relative to Galactic WC5-8 stars at known distance, and analysed in a similar manner, LMC WC4 stars possess systematically higher stellar luminosities,0.2 dex lower wind densities, yet a similar range of surface chemistries. We illustrate how the classification Ciii5696 line is extremely sensitive to wind density, such that this is the principal dierence between the subtype distribution of LMC and Galactic early-type WC stars. Temperature dierences do play a role, but carbon abundance does not aect WC spectral types. We illustrate the eect of varying temperature and mass-loss rate on the WC spectral type for HD 32257 (WC4, LMC) and HD 156385 (WC7, Galaxy) which possess similar abundances and luminosities. Using the latest evolutionary models, pre-supernova stellar masses in the range 11-19 M are anticipated for LMC WC4 stars, with 7-14 M for Galactic WC stars with known distances. These values are consistent with pre-cursors of bright type- Ic supernovae such as SN 1998bw (alias GRB 980425) for which a minimum total mass of C and O of 14 M has been independently derived.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/040dc50d0cda63a9b2dbb9eaf9782faf3d3e4684

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In Astronomy and Astrophysics

1. N. Langer
2. S. Smartt
3. Stan Woosley
4. G. Meynet
5. N. Smith
6. P. Crowther
7. Robert G. Izzard
8. J. Eldridge

Citations in the corpus

• Grids of model spectra for WN stars, ready for use (2004, methodology): “Their models have been applied for the analysis of various stars (e.g., Hillier & Miller 1999; Crowther et al. 2000, 2002; Dessart et al. 2000; Herald et al. 2001).”
• The Galactic WC stars Stellar parameters from spectral analyses indicate a new evolutionary sequence (2012, methodology): “The 16 six WC4 stars in the LMC were analyzed by Gräfener et al. (1998) and Crowther et al. (2002).”
• Progenitors of Core-Collapse Supernovae (2009, background): “These convincingly suggest a spectral type of B3I, a Teff ≃ 15750 (from the calibration of LMC B-supergiants Trundle et al. 2007) and hence log L/L⊙= 5.1 ± 0.1.”
• Lower mass loss rates in O-type stars: Spectral signatures of dense clumps in the wind of two Galactic O4 stars (2004, methodology): “The first evidences of wind clumping were found in WR stars for which small filling factors (f∞ ≈ 0.1) were derived too (Hamann & Koesterke 1998; Hillier & Miller 1999; Crowther et al. 2002a).”
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates (2007, background): “More recent studies (Crowther et al. 2002) prefer even stronger clumping, with filling factors smaller thanfV = 0.1.”
• A census of the Wolf–Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy (2006, background): “The reason for this dichotomy appears to be, at least in part, due to the sensitivity of WC spectral classification to (metallicity-dependent) wind strength (Crowther et al. 2002), rather than elemental abundance differences.”
• Realistic ionizing fluxes for young stellar populations from 0.05 to 2 Z (2002, methodology): “Nevertheless, our adopted T∗ values for WN and WC stars span the range occupied by Galactic and LMC W-R stars, as derived by recent analyses (e.g. Hillier & Miller 1998; Herald et al. 2001; Crowther et al. 2002a).”
• Stellar evolution with rotation XI. Wolf-Rayet star populations at different metallicities (2004, methodology): “Recently Crowther et al. (2002) proposed a metallicity dependence for the mass loss rates of WR stars comparable to that predicted for O-type stars, i.e. with (Z/Z )1/2.”
• Physical Properties of Wolf-Rayet Stars (2006, methodology): “Neon lines are extremely weak in the UV/optical spectrum of WC stars (Crowther et al. 2002), but ground-state fine-structure lines at [Ne ii] 12.8µm and [Ne iii] 15.5µm may be observed via mid-IR spectroscopy, as illustrated for γ Vel in van der Hucht et al. (1996).”
• Evolution of rapidly rotating metal-poor massive stars towards gamma-ray bursts (2005, background): “However, Wolf-Rayet mass loss rates may be smaller for smaller metallicity (Nugis & Lamers 2000 (NL00); Crowther et al. 2002; Vink & de Koter 2005).”
• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, background): “Moreover, half of these WC stars are predicted to evolve from 120 M initial mass, which does not match the low WC luminosities actually observed (Gräfener et al. 1998; Crowther et al. 2002).”
• 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).”
• Strongly star forming galaxies in the local Universe with nebular He iiλ4686 emission (2012, background): “Although we can get direct information at slightly longer wavelengths with space-based ultraviolet (UV) spectroscopy (e.g. Crowther et al. 2002), most of our knowledge about the λ < 912 Å region is based on indirect evidence, even for solar metallicity.”
• The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit (2010, methodology): “Finally, a WC 5 star (Melnick 33Sb) lies at a projected distance of 2.9 pc for which we adopt similar wind properties and ionizing fluxes to single WC 4 stars (Crowther et al. 2002).”
• The Propagation and Eruption of Relativistic Jets from the Stellar Progenitors of Gamma-Ray Bursts (2003, background): “This mass-loss rate is rather low for typical Wolf-Rayet stars of this mass in our Galaxy (Nugis & Lamers 2000), but it might be more appropriate for the low metallicity in the GRB neighborhood (Crowther et al. 2002).”
• Core-collapse explosions of Wolf–Rayet stars and the connection to Type IIb/Ib/Ic supernovae (2011, background): “As evolution and peeling continue, the surface then becomes helium and carbon dominated (yielding a WC star; Dessart et al. 2000; Crowther et al. 2002), and then carbon and oxygen dominated (yielding a WO star; Conti 1976; Maeder & Meynet 1994; Kingsburgh et al. 1995).”
• SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD (2009, methodology): “For BAT9961 (WC4), we use the model presented by Crowther et al. (2002) which has Teff = 52 kK, log L/L = 5.68, v∞ = 3200 km s−1, and Ṁ = 4 × 10−5 M yr−1 for a volume filling factor of 0.1.”