Lower mass loss rates in O-type stars: Spectral signatures of dense clumps in the wind of two Galactic O4 stars

By J. Bouret, T. Lanz, D. John Hillier. 2004

183 citations recorded by the source corpus.

We have analyzed the far-ultraviolet spectrum of two Galactic O4 stars, the O4If+ supergiant HD 190429A and the O4V((f)) dwarf HD 96715, using archival FUSE and IUE data. We have conducted a quantitative analysis using the two NLTE model atmosphere and wind codes,  and , which incorporate a detailed treatment of NLTE metal line blanketing. From the far-UV spectrum, we have derived the stellar and wind parameters and the surface composition of the two stars. The surface of HD 190429A has a composition typical of an evolved O supergiant (nitrogen-rich, carbon and oxygen- poor), while HD 96715 exhibits surface nitrogen enhancement similar to the enrichment found in SMC O dwarfs which has been attributed to rotationally-induced mixing. Following studies of Magellanic Cloud O stars, we find that homogeneous wind mod- els could not match the observed profile of O λ1371 and require very low phosphorus abundance to fit the P λλ1118−1128 resonance lines. We show, on the other hand, that we are able to match the O  and P  lines using clumped wind models. In addition to these lines, we find that N λ1718 is also sensitive to wind clumping. For both stars, we have calculated clumped wind models that match well all these lines from different species and that remain consistent with Hα data. In particular, we have achieved an excellent match of the P  resonance doublet, indicating that our physical description of clumping is adequate. These fits therefore provide a coherent and thus much stronger evidence of wind clumping in O stars than earlier claims. We show that the success of the clumped wind models in matching these lines results from increased recombination in the clumps, hence from a better description of the wind ionization structure. We find that the wind of these two stars is highly clumped, as expressed by very small volume filling factors, namely f∞ = 0.04 for HD 190429A and f∞ = 0.02 for HD 96715. In agreement with our analysis of SMC stars, clumping starts deep in the wind, just above the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more. These lower mass loss rates will affect substantially the evolution of massive stars. Accounting for wind clumping is essential when determining the wind properties of O stars. Our study therefore calls for a fundamental revision in our understanding of mass loss and of O-type star stellar winds.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. N. Smith
2. S. Smartt
3. N. Langer
4. Stan Woosley
5. J. Vink
6. J. Puls
7. P. Crowther
8. F. Najarro

In Instrumentation

1. N. Smith
2. J. Vink
3. N. Langer
4. J. Puls
5. S. Smartt
6. F. Najarro
7. P. Crowther
8. A. Filippenko

Citations in the corpus

• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars (2014, background): “Using UV resonance absorption lines in O-type stars, Fullerton et al. (2006) have proposed a reduction by a factor of 10 or more from traditional mass-loss rates (fcl values of 100 or more), while Bouret et al. (2005) require reductions by factors of ∼3.”
• SPECTRAL EVOLUTION OF THE EXTRAORDINARY TYPE IIn SUPERNOVA 2006gy (2009, background): “The winds are clumped, which lowers the mass-loss rate one derives from observations (see Bouret et al. 2005; Fullerton et al.”
• BLACK HOLE FORMATION IN FAILING CORE-COLLAPSE SUPERNOVAE (2010, background): “Recent observational results suggest that the rates used in current stellar evolution models may be too high by factors of 3− 10 if clumped winds are considered correctly (Bouret et al. 2005; Fullerton et al. 2006; Puls et al. 2006).”
• Probing clumpy stellar winds with a neutron star (2007, background): “There are multiple observational lines of evidence for wind clumping in massive stars from wind line profiles (Bouret et al. 2005; Fullerton et al. 2006), discrete absorption components (Prinja & Howarth 1986), variable line profiles (Lépine & Moffat 1999; Markova et al. 2005), polarimetry (Lupie…”
• X-ray spectroscopy of stars (2009, background): “…stochastic variability of optical lines associated with the wind (e.g. Eversberg et al 1998; Markova et al 2005), model atmosphere fits of UV lines (Bouret et al, 2005), temporal and/or spectral properties of some high-mass X-ray binaries (Sako et al, 2003; van der Meer et al, 2005).”
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit (2008, background): “Note that significant clumping factors in the range of D=10–100 have recently been proposed for OB star winds (Crowther et al. 2002; Hillier et al. 2003; Bouret et al. 2003, 2005; Fullerton et al. 2006).”
• A LIBRARY OF THEORETICAL ULTRAVIOLET SPECTRA OF MASSIVE, HOT STARS FOR EVOLUTIONARY SYNTHESIS (2010, methodology): “Bouret et al. (2005) were able to significantly improve the fit to the O v λ1371 line by introducing clumping in their wind models.”
• Core-collapse explosions of Wolf–Rayet stars and the connection to Type IIb/Ib/Ic supernovae (2011, background): “Recent revisions downwards of massive star steady-state mass-loss rates may challengethis scenario (Bouret et al. 2005).”
• Bright OB stars in the Galaxy. III. Constraints on the radial stratification of the clumping factor (2006, methodology): “Furthermore, the ionization balance becomes modified, primarily because of the additional 〈ρ2〉-dependence of radiative recombination rates (see also Bouret et al. 2005).”
• A Grid of NLTE Line-blanketed Model Atmospheres of Early B-Type Stars (2006, background): “Indeed, many uncertainties still remain in current wind models such as wind clumping (Bouret et al. 2005) and wind ionization by X-rays (e. g., Martins et al. 2005).”
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates (2007, background): “Very strong clumping and consequently low mass-loss rates were also obtained by Bouret et al. (2005) for two O stars analyzed with non-LTE model atmospheres.”
• SN 2006gy: Discovery of the Most Luminous Supernova Ever Recorded, Powered by the Death of an Extremely Massive Star like η Carinae (2006, background): “…studies of line-drivenwinds from O-type stars andWR stars have shown that their winds are highly clumped, requiring that their mass-loss rates through line-driven winds on themain sequence could be an order ofmagnitude lower than previously believed (Fullerton et al. 2006; Bouret et al. 2005).”
• The most massive stars in the Arches cluster (2007, background): “As previously recalled, we note however that recent studies indicate smallerf for O supergiants (Crowther et al. 2002a; Hillier et al. 2003; Bouret et al. 2005).”
• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars (2007, background): “…spectroscopy of He ii λ4686 in ζ Pup, and by Crowther et al. (2002); Hillier et al. (2003); Bouret et al. (2003); Massa et al. (2003); Martins et al. (2004, 2005); Bouret et al. (2005), and Fullerton et al. (2006) from analysis of UV (resonance) lines, partly in combination with optical lines.”
• Stellar and wind properties of massive stars in the central parsec of the Galaxy (2006, background): “Comparison data from Crowther et al. (1995b), Crowther et al. (1995c), Morris et al. (2000) for WN stars and Repolust et al. (2004), Bouret et al. (2005) for O supergiants are shown by open symbols.”
• Wave‐driven mass loss in the last year of stellar evolution: setting the stage for the most luminous core‐collapse supernovae (2012, background): “Many massive stars appear to lose a significant fraction of their mass in episodic outbursts rather than continuous line-driven winds (e.g., Bouret et al. 2005; Smith & Owocki 2006).”
• THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR (2012, background): “The upper limit of the main-sequence mass may be even larger according to recent stellar wind massloss rates (see Bouret et al. 2005; Eldridge & Vink 2006; Fullerton et al. 2006).”
• High-mass X-ray binaries in the Milky Way (2013, background): “Besides multiple observational evidence (Bouret et al. 2005; Fullerton et al. 2006; Prinja & Howarth 1986; L’epine & Moffat 1999; Markova et al. 2005; Lupie & Nordsieck 1987; Davies et al. 2007; Cassinelli & Olson 1979; Oskinova et al. 2006), wind clumping is still poorly constrained.”