Bright OB stars in the Galaxy. III. Constraints on the radial stratification of the clumping factor

By J. Puls, N. Markova, S. Scuderi, C. Stanghellini, O. G. Taranova, A. W. Burnley, I. Howarth. 2006

198 citations recorded by the source corpus.

Context. Recent results strongly challenge the canonical picture of massive star winds: various evidence indicates that currently accepted mass-loss rates, u M, may need to be revised downwards, by factors extending to one magnitude or even more. This is because the most commonly used mass-loss diagnostics are affected by “clumping” (small-scale density inhomogeneities), influencing our interpretation of observed spectra and fluxes. Aims. Such downward revisions would have dramatic consequences for the evolution of, and feedback from, massive stars, and thus robust determinations of the clumping properties and mass-loss rates are urgently needed. We present a first attempt concerning this objective, by means of constraining the radial stratification of the so-called clumping factor. Methods. To this end, we have analyzed a sample of 19 Galactic O-type supergiants/giants, by combining our own and archival data for Hα, IR, mm and radio fluxes, and using approximate methods, calibrated to more sophisticated models. Clumping has been included into our analysis in the “conventional” way, by assuming the inter-clump matter to be void. Because (almost) all our diagnostics depends on the square of density, we cannot derive absolute clumping factors, but only factors normalized to a certain minimum. Results. This minimum was usually found to be located in the outermost, radio-emitting region, i.e., the radio mass-loss rates are the lowest ones, compared to u M derived from Hα and the IR. The radio rates agree well with those predicted by theory, but are only upper limits, due to unknown clumping in the outer wind. Hα turned out to be a useful tool to derive the clumping properties inside r < 3 ... 5R� . Our most important result concerns a (physical) difference between denser and thinner winds: for denser winds, the innermost region is more strongly clumped than the outermost one (with a normalized clumping factor of 4.1 ± 1.4), whereas thinner winds have similar clumping properties in the inner and outer regions. Conclusions. Our findings are compared with theoretical predictions, and the implications are discussed in detail, by assuming different scenarios regarding the still unknown clumping properties of the outer wind.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/11de68d1239c264b58178d80ee2461b998472e49

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In Astronomy and Astrophysics

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

Citations in the corpus

• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars (2007, background): “In addition to these purely spectroscopic investigations, Puls et al. (2006) analyzed a sample of Galactic O-type (super)giants more recently, combining Hα, infrared, mm and radio fluxes to derive constraints on the radial stratification of the clumping factor.”
• 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).”
• Observed Fractions of Core-Collapse Supernova Types and Initial Masses of their Single and Binary Progenitor Stars (2010, background): “Recent work (Bouret et al. 2005; Fullerton et al. 2006; Puls et al. 2006) has demonstrated that O-star winds are clumped and that their mass-loss rates are too weak, so it appears likely that LBV giant eruptions must dominate this mass-loss if WR stars are to form via single-star evolution (Smith &…”
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates (2007, methodology): “Puls et al. (2006) studied the O-type supergiantζ Puppis and found that the mass-loss rates derived from Hα and from IR/radio continuum emission can only be reconciled if the wind is strongly clumped (D ≈ 5.5) already at a radius of 1.”
• Sub-surface convection zones in hot massive stars and their observable consequences (2009, background): “Moreover, if there was any dependence on wind density predicted at all, optically thin winds should be more strongly clumped than optically thick winds (Owocki & Puls 1999; Puls et al. 2006).”
• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, background): “The value D = 10 is not accurately constrained, and may in fact vary from star to star or as function of radius (Nugis et al. 1998; Puls et al. 2006; Liermann & Hamann 2008).”
• The most massive stars in the Arches cluster (2007, background): “This is in agreement (qualitatively and quantitatively) with the recent findings of Puls et al. (2006) and with the theoretical predictions of Runacres & Owocki (2002).”
• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars (2014, methodology): “…the theoretical mind momentum 8 Smith relation, both Repolust et al. (2004) and Markova et al. (2004) found fcl=5, or a mass-loss raduction by 2.3.1 Puls et al. (2006, 2008) and others have discussed that the larger mass-loss rate reduction of 10 found by Fullerton et al. (2006) may be an…”
• SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD (2009, background): “More recently, Puls et al. (2006) argued that this very sensitivity makes mid-infrared emission extremely important in disentangling the nature of clumped winds.”