An X-ray Study of Two B+B Binaries: AH Cep and CW Cep

TL;DR

This study uses Chandra X-ray observations to analyze two early B-type binary systems, AH Cep and CW Cep, revealing differing X-ray emissions that suggest complex wind interactions or magnetic activity.

Contribution

It provides the first X-ray luminosity measurements for AH Cep and CW Cep, highlighting unexpected non-detection in CW Cep and proposing magnetic activity as a possible X-ray source in AH Cep.

Findings

AH Cep detected with X-ray luminosity consistent with wind shocks or collision.

CW Cep not detected, setting an upper limit on X-ray luminosity.

AH Cep's X-ray emission may originate from magnetism rather than standard wind shocks.

Abstract

AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8~d and 2.7~d, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B~stars. {\em Chandra} ACIS-I observations were obtained to determine X-ray luminosities. AH~Cep was detected with an unabsorbed X-ray luminosity at a 90\% confidence interval of $(9-33)\times 10^{30}$ erg s$^{-1}$, or $(0.5-1.7)\times 10^{-7} L_{\rm Bol}$, relative to the combined Bolometric luminosities of the two components. While formally consistent with expectations for embedded wind shocks, or binary wind collision, the near-twin system of CW~Cep was a surprising non-detection. For CW~Cep, an upper limit was determined with $L_X/L_{\rm Bol} < 10^{-8}$, again for the combined components. One difference between these two systems is that AH~Cep is part of a multiple system. The X-rays from AH~Cep may not arise from standard wind shocks nor wind collision, but perhaps instead from magnetism in any one of the four components of the system. The possibility could be tested by searching for cyclic X-ray variability in AH~Cep on the short orbital period of the inner B~stars.