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2006ApJ...637.1025F - Astrophys. J., 637, 1025-1039 (2006/February-1)

The discordance of mass-loss estimates for galactic O-type stars.


Abstract (from CDS):

We have determined accurate values of the product of the mass-loss rate and the ion fraction of P+4, M{dot}q(P+4), for a sample of 40 Galactic O-type stars by fitting stellar wind profiles to observations of the P V resonance doublet obtained with FUSE, ORFEUS BEFS, and Copernicus. When P+4 is the dominant ion in the wind [i.e., 0.5≲q(P+4)≤1], M{dot}q(P+4) approximates the mass-loss rate to within a factor of ≲2. Theory predicts that P+4 is the dominant ion in the winds of O7-O9.7 stars, although an empirical estimator suggests that the range O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P V wind profiles are systematically smaller than those obtained from fits to Hα emission profiles or radio free-free emission by median factors of ∼130 (if P+4 is dominant between O7 and O9.7) or ∼20 (if P+4 is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from ``ρ2'' diagnostics have been systematically overestimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.

Abstract Copyright:

Journal keyword(s): Stars: Early-Type - Stars: Mass Loss - Stars: Winds, Outflows

Simbad objects: 42

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