Signature of wide-spread clumping in B supergiant winds

TL;DR

This study investigates spectral line ratios in B supergiant winds to identify signatures of clumping, revealing widespread wind inhomogeneities and offering a method to quantify wind porosity.

Contribution

It introduces a novel analysis of SiIV doublet line ratios to detect and quantify wind clumping in B supergiants, enhancing mass-loss rate estimations.

Findings

Line ratios vary between 1 and 2, indicating clumping.

Spectroscopic signatures confirm widespread wind clumping.

Method allows quantification of wind porosity.

Abstract

We seek to establish additional observational signatures of the effects of clumping in OB star winds. The action of clumping on strategic wind-formed spectral lines is tested to steer the development of models for clumped winds and thus improve the reliability of mass-loss determinations for massive stars.The SiIV 1400 resonance line doublets of B0 to B5 supergiants are analysed using empirical line-synthesis models. The focus is on decoding information on wind clumping from measurements of ratios of the radial optical depths (tau_(rad)(w)) of the red and blue components of the SiIV doublet. We exploit in particular the fact that the two doublet components are decoupled and formed independently for targets with relatively low wind terminal velocities. Line-synthesis analyses reveal that the mean ratio of tau_(rad)(w) of the blue to red SiIV components are rarely close to the canonical value of ~ 2 (expected from atomic constants), and spread instead over a range of values between ~1 and 2. These results are interpreted in terms of a photosphere that is partially obscured by optically thick structures in the outflowing gas.The spectroscopic signatures established in this study demonstrate the wide-spread existence of wind clumping in B supergiants. The additional information in unsaturated doublet profiles provides a means to quantify the porosity of the winds.