A Coordinated X-ray and Optical Campaign on the Nearest Massive Eclipsing Binary, Delta Ori Aa: I. Overview of the X-ray Spectrum

M. F. Corcoran$^{1,2}$, J. S. Nichols$^{3}$, H. Pablo$^{4}$, T. Shenar$^{5}$, A. M. T. Pollock$^{6}$, W. L. Waldron$^{7}$, A. F. J. Moffat$^{4}$, N. D. Richardson$^{4}$, C. M. P. Russell$^{8}$, K. Hamaguchi$^{1,9}$, D. P. Huenemoerder$^{10}$, L. Oskinova$^{5}$, W.-R. Hamann$^{5}$, Y. Naz'e$^{11, 23}$, R. Ignace$^{12}$, N. R. Evans$^{13}$, J. R. Lomax$^{14}$, J. L. Hoffman$^{15}$, K. Gayley$^{16}$, S. P. Owocki$^{17}$, M. Leutenegger$^{1,9}$, T. R. Gull$^{18}$, K. T. Hole$^{19}$, J. Lauer$^{3}$, & R. C. Iping$^{20,21}$

1 - CRESST and X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA; 2 - Universities Space Research Association, 7178 Columbia Gateway Dr. Columbia, MD 21046, USA; 3 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 34, Cambridge, MA 02138, USA; 4 - D'epartement de physique and Centre de Recherche en Astrophysique du Qu'ebec (CRAQ), Universit'e de Montr'eal, C.P. 6128, Succ.~Centre-Ville, Montr'eal, Qu'ebec, H3C 3J7, Canada; 5 - Institut f"ur Physik und Astronomie, Universit"at Potsdam, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany; 6 - European Space Agency, textit{XMM-Newton}; Science Operations Centre, European Space Astronomy Centre, Apartado 78, E-28691 Villanueva de la Ca~{n}; ada, Spain; 7 - Eureka Scientific, Inc., 2452 Delmer St., Oakland, CA 94602, USA; 8 - NASA-GSFC, Code 662, Goddard Space Flight Center, Greenbelt, MD, 20771 USA; 9 - Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA; 10 - Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 USA; 11 - Groupe d'Astrophysique des Hautes Energies, Institut d'Astrophysique et de G'eophysique, Universit'e de Li'ege, 17, All'{e}e du 6 Ao^{u}t, B5c, B-4000 Sart Tilman, Belgium; 12 - Physics and Astronomy, East Tennessee State University, Johnson City, TN 37614, USA.; 13 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 4, Cambridge, MA 02138, USA; 14 - Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, OK, 73019, USA; 15 - Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Avenue, Denver, CO, 80208, USA; 16 - Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA; 17 - University of Delaware, Bartol Research Institute, Newark, DE 19716, USA; 18 - Laboratory for Extraterrestrial Planets and Stellar Astrophysics, Code 667, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA; 19 - Department of Physics, Weber State University, 2508 University Circle, Ogden, UT 84408, USA; 20 - CRESST and Observational Cosmology Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA; 21 - Department of Astronomy, University of Maryland, 1113 Physical Sciences Complex, College Park, MD 20742-2421, USA; 22 - FNRS Research Associate.

We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of Delta Ori A. Delta Ori A is actually a triple system which includes the nearest massive eclipsing spectroscopic binary, Delta Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, Delta Ori Aa2, has a much lower X-ray luminosity than the brighter primary (Delta Ori Aa1), Delta Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around Delta Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneous with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3-0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.

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

Weblink: http://arxiv.org/abs/1507.05101

Comments: Other papers in the series are:

II. X-ray Variability, Nichols et al., 2015, ApJ, in press ( arXiv:1507.04972)

III. Analysis of Optical Photometric MOST and Spectroscopic (Ground Based) Variations, Pablo et al., 2015, ApJ, in press ( arXiv:1504.08002)

IV. A multiwavelength, non-LTE spectroscopic analysis, Shenar et al,, 2015, ApJ, in press ( arXiv:1503.03476)

Email: michael.f.corcoran@nasa.gov