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

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. 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) × 10L 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 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.

Modelling of the B-type binaries CW Cephei and U Ophiuchi

“…CW Cep is also characterised as an intrinsically variable polarised object (Elias et al 2008). Both CW Cep and another early B+B binary system AH Cep, were observed with the Chandra X-ray Telescope in search of evidence of a wind-wind collision (Ignace et al 2017). Although CW Cep and AH Cep are comprised of stars with similar properties (cf.…”

“…Pavlovski et al 2018), X-rays were only detected for AH Cep, even though it is nearly a factor of 2 further away than CW Cep. The authors could not disentangle whether the X-rays detected from AH Cep were caused by colliding winds, or perhaps from magnetic activity originating in one of the other components of the quadruple system of AH Cep (Ignace et al 2017).…”

Physical properties and CNO abundances for high-mass stars in four main-sequence detached eclipsing binaries: V478 Cyg, AH Cep, V453 Cyg and V578 Mon

“…2 There is a numerical error in the calculation of the uncertainties in Burkholder et al (1997) as they used an inclination of i = 69.2 o ± 12 o instead of the value of i = 69.21 ± 0.12 given by Bell et al (1986). Ignace et al (2017) analysed Chandra observations and found X-ray variability. They also studied CW Cep, a binary system with very similar physical properties to AH Cep.…”

Modelling of the B-type binaries CW Cep and U Oph: A critical view on dynamical masses, core boundary mixing, and core mass

“…Pavlovski et al (2018)), X-rays were only detected for AH Cep, despite it being nearly a factor 2 further away than CW Cep. The authors could not disentangle, however, whether the X-rays detected from AH Cep were caused by colliding winds, or perhaps from magnetic activity originating in one of the other components of the quadruple system of AH Cep (Ignace et al 2017).…”

“…CW Cep is also characterised as an intrinsically variable polarized object (Elias et al 2008). Both CW Cep and another early B+B binary system AH Cep, were observed with the Chandra X-ray Telescope in search for evidence of a wind-wind collision (Ignace et al 2017). Although CW Cep and AH Cep are comprised of stars with similar properties (c.f.…”