The Discordance of Mass-Loss Estimates for O-Type Stars

Details The Discordance of Mass-Loss Estimates for O-Type Stars The Discordance of Mass-Loss Estimates for O-Type Stars

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...205.5304f&link_type=abstract

American Astronomical Society Meeting 205, #53.04; Bulletin of the American Astronomical Society, Vol. 36, p.1425

Astronomy and Astrophysics

Astronomy

2

Scientific paper

Although the UV resonance lines of ionized metals are the most sensitive indicators of the stellar winds of O-type stars, the wind lines accessible to IUE or HST do not provide reliable estimates of the mass-loss rate. The utility of these diagnostics is compromised because they are due to (a) dominant ions of abundant elements (e.g., C3+), and are generally saturated; or (b) trace ions (e.g., Si3+), whose abundances depend sensitively on local conditions in the wind, including the presence of X-rays. Consequently, mass-loss rates are typically derived from observations of emission in Hα or the radio continuum. However, determinations based on these ``density-squared" diagnostics are quite sensitive to the presence of inhomogeneities, and will over-estimate the true mass flux if the wind is clumped.
To circumvent these problems, we have used new FUSE and archival Copernicus and Orfeus observations of the P v resonance doublet to estimate mass-loss rates for a standard sample of Galactic O-type stars. Since P4+ is expected to be the dominant ion in the winds of mid-O stars, its ion fraction is known a priori; and, since P is much less abundant than C or N, its resonance lines are not saturated and provide reliable measurements of the ionic column density. The mass-loss rates derived from P v wind profiles are typically 1--2 orders of magnitude smaller than those obtained from Hα or radio observations. We interpret this discrepancy as an indication that the winds of O-type stars are strongly clumped.
The NASA-CNES-CSA FUSE mission is operated for NASA by the Johns Hopkins University. Financial support for this work was provided by NASA FUSE Guest Investigator program.

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