A Coordinated X-ray and Optical Campaign of the Nearby Massive Binary $\delta$ Orionis Aa: II. X-ray Variability

Abstract

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral dataset of the $\delta$ Orionis Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ~479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range 5-25 $\mathring{A}$ is confirmed, with maximum amplitude of about +/-15% within a single ~125 ks observation. Periods of 4.76d and 2.04d are found in the total X-ray flux, as well as an apparent overall increase in flux level throughout the 9-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phase=0.0 when the secondary $\delta$ Orionis Aa2 is at inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.

36 pages, 14 Tables, 19 Figures, accepted by ApJ, one of 4 related papers to be published together

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Cited by in corpus (13)

• A coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, $\delta$ Orionis Aa: IV. A multiwavelength, non-LTE spectroscopic analysis
• Variability of OB stars from TESS southern Sectors 1-13 and high-resolution IACOB and OWN spectroscopy
• A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, delta Orionis Aa: III. Analysis of Optical Photometric MOST and Spectroscopic (Ground Based) Variations
• The 155-day X-ray cycle of the very massive Wolf-Rayet star Melnick 34 in the Large Magellanic Cloud
• Probing Wolf-Rayet Winds: Chandra/HETG X-Ray Spectra of WR 6
• X-ray diagnostics of massive star winds
• Coordinated UV and X-ray spectroscopic observations of the O-type giant xi Per: the connection between X-rays and large-scale wind structure
• A Coordinated X-ray and Optical Campaign on the Nearest Massive Eclipsing Binary, Delta Ori Aa: I. Overview of the X-ray Spectrum
• Spectrum of the secondary component and new orbital elements of the massive triple star Delta Ori A
• WASP-12b: A Mass-Losing Extremely Hot Jupiter
• An X-ray Study of Two B+B Binaries: AH Cep and CW Cep
• VLTI observations of the Orion Belt stars: I. eps Orionis
• X-ray diagnostics of massive star winds