Signature of wide-spread clumping in B supergiant winds

摘要

Aims. We seek to establish additional observationalsignatures of the effects of clumping in OBstar winds. The actionof clumping on strategic wind-formed spectral lines is tested to steerthe development of models for clumped winds and thus improve thereliability of mass-loss determinations for massive stars. Methods. The Si IV 1400resonance line doublets ofB0 to B5supergiants are analysedusing empirical line-synthesis models. The focus is on decodinginformation on wind clumping from measurements of ratios of the radialoptical depths()of the red and blue components of the Si IVdoublet.We exploit in particular the fact that the two doublet components aredecoupled and formed independently for targets with relatively low windterminal velocities. Results. Line-synthesis analyses reveal that the mean ratio of of the blue to red Si IVcomponents are rarely close to the canonical value of2 (expected from atomic constants), and spread instead over a range of values between1and2. These results are interpreted in terms of a photospherethat is partially obscured by optically thick structures in theoutflowing gas. Conclusions. The spectroscopic signatures established in thisstudy demonstrate the wide-spread existence of wind clumping inBsupergiants. The additional information in unsaturated doubletprofiles provides a means to quantify the porosity of thewinds. Key words: stars: early-type - stars: mass-loss - ultraviolet: stars