AAS 205th Meeting, 9-13 January 2005
Session 53 Hot Stars, Atmospheres and Winds
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

## [53.04] The Discordance of Mass-Loss Estimates for O-Type Stars

A. W. Fullerton (UVic/JHU), D. L. Massa (SGT, Inc.), R. K. Prinja (UCL)

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 H\alpha 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~{\sc 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~{\sc v} wind profiles are typically 1--2 orders of magnitude smaller than those obtained from H\alpha 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.

Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.