The Discordance of Mass-Loss Estimates for Galactic O-Type Stars
Abstract
We have determined accurate values of the product of the mass-loss rate and the ion fraction of P+4, M˙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˙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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2006
- DOI:
- 10.1086/498560
- arXiv:
- arXiv:astro-ph/0510252
- Bibcode:
- 2006ApJ...637.1025F
- Keywords:
-
- Stars: Early-Type;
- Stars: Mass Loss;
- Stars: Winds;
- Outflows;
- Astrophysics
- E-Print:
- 26 pages, 4 figures