Carina OB Stars: X-ray Signatures of Wind Shocks and Magnetic Fields

TL;DR

This study analyzes X-ray signatures of wind shocks and magnetic fields in OB stars within the Carina complex, identifying candidates for magnetic confinement and binary interactions, and expanding understanding of stellar X-ray emission mechanisms.

Contribution

It provides a comprehensive optical/X-ray database and identifies new candidate magnetic and binary OB stars with unusual X-ray properties.

Findings

High-temperature X-ray sources suggest magnetic confinement in some O stars.

Detection of strong, variable X-rays indicates possible binary systems.

Some B stars' X-ray emissions cannot be explained by unseen companions, hinting at intrinsic sources.

Abstract

The Chandra Carina Complex contains 200 known O- and B type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical Lx/Lbol relation, or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary, and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403 and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high Lx cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.