The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars

Abstract

A primary goal of the FUSE mission is to understand the origin of the O VI ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along sightlines to OB-type stars, these interstellar components are usually blended with O VI stellar wind profiles, which frequently vary in shape. In order to assess the effects of this time-dependent blending on measurements of the interstellar O VI lines, we have undertaken a mini-survey of repeated observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud. These sparse time series, which consist of 2-3 observations separated by intervals ranging from a few days to several months, show that wind variability occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does in other resonance lines. However, in the interstellar O VI $\lambda$1032 region, the O VI $\lambda$1038 wind varies only in $\sim$30% of the cases. By examining cases exhibiting large amplitude variations, we conclude that stellar-wind variability {\em generally} introduces negligible uncertainty for single interstellar O VI components along Galactic lines of sight, but can result in substantial errors in measurements of broader components or blends of components like those typically observed toward stars in the Large Magellanic Cloud. Due to possible contamination by discrete absorption components in the stellar O VI line, stars with terminal velocities greater than or equal to the doublet separation (1654 km/s) should be treated with care.

Accepted for publication in the Astrophysical Journal Letter

Cited by in corpus (11)

• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• An Atlas of Galactic Spectra Observed with the Far Ultraviolet Spectroscopic Explorer
• Highly ionised plasma in the Large Magellanic Cloud: Evidence for outflows and a possible galactic wind
• The Global Content, Distribution, and Kinematics of Interstellar O VI in the Large Magellanic Cloud
• FUSE Observations of the Magellanic Bridge Gas toward Two Early-Type Stars: Molecules, Physical Conditions, and Relative Abundance
• Fundamental Properties of the Highly Ionized Plasmas in the Milky Way
• Intermediate-velocity gas observed towards the Shajn 147 SNR
• Survey of O VI absorption in the Large Magellanic Cloud
• Small-Scale Structure of O VI Interstellar Gas in the Direction of the Globular Cluster NGC 6752
• A Search for O VI in the Winds of B-Type Stars
• The distribution and kinematics of interstellar O~{\small VI} in the Milky Way}