A Chandra Observation of the Eclipsing Wolf-Rayet Binary CQ Cep

Abstract

The short-period (1.64 d) near-contact eclipsing WN6+O9 binary system CQ Cep provides an ideal laboratory for testing the predictions of X-ray colliding wind shock theory at close separation where the winds may not have reached terminal speeds before colliding. We present results of a Chandra X-ray observation of CQ Cep spanning ~1 day during which a simultaneous Chandra optical light curve was acquired. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T > 20 MK) will form on or near the line-of-centers between the stars. The X-ray spectrum is strikingly similar to apparently single WN6 stars such as WR 134 and spectral lines reveal plasma over a broad range of temperatures T ~ 4 - 40 MK. A deep optical eclipse was seen as the O star passed in front of the Wolf-Rayet star and we determine an orbital period P = 1.6412400 d. Somewhat surprisingly, no significant X-ray variability was detected. This implies that the hottest X-ray plasma is not confined to the region between the stars, at odds with the colliding wind picture and suggesting that other X-ray production mechanisms may be at work. Hydrodynamic simulations that account for such effects as radiative cooling and orbital motion will be needed to determine if the new Chandra results can be reconciled with the colliding wind picture.

31 pages, 4 figures

References in corpus (12)

• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: I. Isothermal, Nonrotating, Radially Driven Flow
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• High resolution X-Ray spectroscopy of Zeta Puppis with the XMM-Newton Reflection Grating Spectrometer
• Detection of Doppler Shifted X-ray Line Profiles from the Wind of Zeta Puppis (O4f)
• Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma Velorum
• X-ray Emission from Nitrogen-Type Wolf-Rayet Stars
• X-rays from Colliding Stellar Winds: the case of close WR+O binary systems
• New X-ray Detections of WNL Stars
• Observations of Binary and Single Wolf-Rayet Stars with XMM-Newton and Chandra
• XMM-Newton X-ray Observations of the Wolf-Rayet Binary System WR 147
• Chandra HETG Observations of the Colliding Stellar Wind System WR 147
• New Constraints on the Origin of the Short-Term Cyclical Variability of the Wolf-Rayet Star WR 46

Cited by in corpus (6)

• X-ray emission from interacting massive binaries: a review of 15 years of progress
• A changing wind collision
• TRES Survey of Variable Diffuse Interstellar Bands
• X-rays from the oxygen-type Wolf-Rayet binary WR30a
• Unraveling the nature of a deeply embedded Wolf-Rayet star WR 121a
• High Energy Processes in Wolf-Rayet Stars