Multiwavelength Observations of the Runaway Binary HD 15137

TL;DR

This study investigates the runaway binary HD 15137 through optical and X-ray observations, constraining the nature of its potential compact companion and exploring its ejection mechanism from its birth cluster.

Contribution

It provides new orbital parameters, X-ray spectral analysis, and limits on the presence of a compact object in HD 15137, enhancing understanding of its ejection and composition.

Findings

X-ray emission is consistent with an isolated O star.

No evidence of a quiescent neutron star or weakly accreting neutron star.

Constraints suggest the possible presence of a neutron star in the ejector regime or a quiescent black hole.

Abstract

HD 15137 is an intriguing runaway O-type binary system that offers a rare opportunity to explore the mechanism by which it was ejected from the open cluster of its birth. Here we present recent blue optical spectra of HD 15137 and derive a new orbital solution for the spectroscopic binary and physical parameters of the O star primary. We also present the first XMM-Newton observations of the system. Fits of the EPIC spectra indicate soft, thermal X-ray emission consistent with an isolated O star. Upper limits on the undetected hard X-ray emission place limits on the emission from a proposed compact companion in the system, and we rule out a quiescent neutron star in the propellor regime or a weakly accreting neutron star. An unevolved secondary companion is also not detected in our optical spectra of the binary, and it is difficult to conclude that a gravitational interaction could have ejected this runaway binary with a low mass optical star. HD 15137 may contain an elusive neutron star in the ejector regime or a quiescent black hole with conditions unfavorable for accretion at the time of our observations.