Observational evidence for a correlation between macroturbulent broadening and line-profile variations in OB Supergiants

TL;DR

This study provides observational evidence linking macroturbulent broadening to line-profile variations in OB supergiants, suggesting stellar oscillations as a plausible cause for the observed spectral features.

Contribution

It is the first to demonstrate a strong correlation between macroturbulent broadening and line-profile variability in OB supergiants, supporting the oscillation hypothesis.

Findings

Strong correlation between broadening and line-profile variations.

Evidence supports stellar oscillations as the cause.

Results based on a sample of 13 supergiants.

Abstract

The spectra of O and B supergiants are known to be affected by a significant form of extra line broadening (usually referred to as macroturbulence) in addition to that produced by stellar rotation. Recent analyses of high resolution spectra have shown that the interpretation of this line broadening as a consequence of large scale turbulent motions would imply highly supersonic velocity fields in photospheric regions, making this scenario quite improbable. Stellar oscillations have been proposed as a likely alternative explanation. As part of a long term observational project, we are investigating the macroturbulent broadening in O and B supergiants and its possible connection with spectroscopic variability phenomena and stellar oscillations. In this letter, we present the first encouraging results of our project, namely firm observational evidence for a strong correlation between the extra broadening and photospheric line-profile variations in a sample of 13 supergiants with spectral types ranging from O9.5 to B8.