Are the O stars in WR+O binaries exceptionally rapid rotators?

TL;DR

This study investigates whether O stars in WR+O binaries are unusually fast rotators, finding that previous claims of rapid rotation are likely due to measurement artifacts, and that their rotation rates are comparable to normal O stars.

Contribution

The paper challenges prior assertions of exceptional rapid rotation in WR+O binaries by reanalyzing spectral data and demonstrating that their rotation rates are consistent with typical O stars.

Findings

Reanalysis of spectra shows previous claims of supersynchronous rotation are likely due to normalization issues.

Synthetic spectra indicate observed line widths are consistent with normal O star rotation.

The apparent rapid rotation in some WR+O binaries is not exceptional but within normal variation.

Abstract

We examine claims of strong gravity-darkening effects in the O-star components of WR+O binaries. We generate synthetic spectra for a wide range of parameters, and show that the line-width results are consistent with extensive measurements of O stars that are either single or are members of `normal' binaries. By contrast, the WR+O results are at the extremes of, or outside, the distributions of both models and other observations. Remeasurement of the WR+O spectra shows that they can be reconciled with other results by judicious choice of pseudo-continuum normalization. With this interpretation, the supersynchronous rotation previously noted for the O-star components in the WR+O binaries with the longest orbital periods appears to be unexceptional. Our investigation is therefore consistent with the aphorism that if the title of a paper ends with a question mark, the answer is probably `no'.