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

J. Nichols$^{1}$, D. P. Huenemoerder$^{2}$, M. F. Corcoran$^{3}$, W. Waldron$^{4}$, Y. Naz'e$^{5}$, A. M. T. Pollock$^{6}$, A. F. J. Moffat$^{7}$, J. Lauer$^{1}$, T. Shenar$^{8}$, C. M. P. Russell$^{15,16}$, N. D. Richardson$^{7}$, H. Pablo$^{7}$, N. R. Evans$^{1}$, K. Hamaguchi$^{3,9}$,T. Gull$^{10}$, W.-R. Hamann $^{8}$, L. Oskinova$^{8}$, R. Ignace $^{11}$, Jennifer L. Hoffman$^{12}$, K. T. Hole$^{13}$, and J. R. Lomax$^{14}$

1 - Harvard-SmithsonianCenter for Astrophysics, Cambridge, MA, USA; 2 - Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA, USA; 3 - USRA CRESST, Universities Space Research Association, GSFC; 4 - Eureka Scientific, Inc, 2452 Delmer St., Oakland, CA 94602; 5 - FNRS/Dept AGO, Univ. of Li`ege, All'ee du 6 Ao^ut 19c B5C, 4000-Li`ege, Belgium; 6 - European Space Agency, textit{XMM-Newton} Science Operations Centre, European Space Astronomy Centre, Apartado 78, 28691 Villanueva de la Ca {n; ada, Spain; 7 - D'epartement de physique, Universit'e de Montr'eal,C.P. 6128, Succ. C.-V., QC, H3C 3J7, Canada; 8 - Institut f"ur Physik und Astronomie, Universit"at Potsdam, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany; 9 - Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA; 10 - Code 667, NASA/GSFC, Greenbelt, MD 20771 USA; 11 - Physics & Astronomy, East Tennessee State University, Johnson City, TN 37614 USA; 12 - Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, CO, 80208 USA; 13 - Department of Physics, Weber State University, 2508 University Circle, Ogden, UT 84408; 14 - Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK, 73019 USA

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral dataset of the Delta Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of $approx$479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range 5-25 Ang. is confirmed, with maximum amplitude of about $pm$15% within a single $approx$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, Si, and Ne. 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 Ori 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.

Reference: ApJ (in press)
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1507.04972


Email: michael.f.corcoran@nasa.gov