Wind line variability and intrinsic errors in observational mass loss rates

TL;DR

This paper investigates UV wind line variability in OB stars, demonstrating that intrinsic errors in mass loss rate measurements can be significant due to large, dense structures causing profile variations, which impact the reliability of single-observation estimates.

Contribution

It introduces a simple model to translate UV wind line profile variations into mass loss rate uncertainties, highlighting the intrinsic errors and variability in measurements.

Findings

Mass loss rate measurements can vary by factors of 3 or more.

Profile variations are caused by large, dense structures near the photosphere.

Rates from non-simultaneous observations may not agree.

Abstract

UV wind line variability in OB stars appears to be universal. We review the evidence that the variability is due to large, dense, optically thick structures rooted in or near the photosphere. Using repeated bservations and a simple model we translate observed profile variations into optical depth variations and, consequently, variations in measured mass loss rates. Although global rates may be stable, measured rates vary. Consequently, profile variations infer how mass loss rates determined from UV wind lines vary. These variations quantify the intrinsic error inherent in any mass loss rate derived from a single observation. These derived rates can differ by factors of 3 or more. Our results also imply that rates from non-simultaneous observations (such as UV and ground based data) need not agree. Finally, we use our results to examine the nature of the structures responsible for the variability.