Radio Proper Motions of Wolf-Rayet Stars

TL;DR

This study uses archival radio observations spanning 10-20 years to measure the proper motions of six Wolf-Rayet stars, providing new data and insights into their kinematics and origins.

Contribution

It introduces a method to accurately determine proper motions of Wolf-Rayet stars from radio data and reports first measurements for five stars, enhancing understanding of their dynamics.

Findings

Proper motions for five Wolf-Rayet stars are reported for the first time.

The proper motion of WR 145a (Cyg X-3) suggests a formation via direct collapse.

The method yields more accurate proper motions than previous measurements for WR 140.

Abstract

We present the analysis of observations taken from the Very Large Array archive of six Wolf-Rayet stars with radio emission, with the purpose of determining their proper motions. Typically, these observations cover periods of 10 to 20 years. To verify the method, we included WR 140 in the sample, finding that the proper motions determined by us are a few times more accurate than and consistent within noise with those of Hipparcos. The other five WR stars were not studied by Hipparcos and we report their proper motions for the first time. The proper motions for WR 145a = Cyg X-3 are consistent with the source being stationary with respect to its local standard of rest and suggest that the black hole in this binary system formed by direct collapse of a massive star, without expulsion of a supernova remnant.