TY  - JOUR
A1  - Corcoran, Michael F.
A1  - Nichols, Joy S.
A1  - Pablo, Herbert
A1  - Shenar, Tomer
A1  - Pollock, Andy M. T.
A1  - Waldron, Wayne L.
A1  - Moffat, Anthony F. J.
A1  - Richardson, Noel D.
A1  - Russell, Christopher M. P.
A1  - Hamaguchi, Kenji
A1  - Huenemoerder, David P.
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Naze, Yael
A1  - Ignace, Richard
A1  - Evans, Nancy Remage
A1  - Lomax, Jamie R.
A1  - Hoffman, Jennifer L.
A1  - Gayley, Kenneth
A1  - Owocki, Stanley P.
A1  - Leutenegger, Maurice
A1  - Gull, Theodore R.
A1  - Hole, Karen Tabetha
A1  - Lauer, Jennifer
A1  - Iping, Rosina C.
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. I. Overview of thr X-Ray spectrum
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - 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 that 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 simultaneously 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.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual (Delta Ori)
KW  - stars: mass-loss
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/132
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Nichols, Joy
A1  - Huenemoerder, David P.
A1  - Corcoran, Michael F.
A1  - Waldron, Wayne
A1  - Naze, Yael
A1  - Pollock, Andy M. T.
A1  - Moffat, Anthony F. J.
A1  - Lauer, Jennifer
A1  - Shenar, Tomer
A1  - Russell, Christopher M. P.
A1  - Richardson, Noel D.
A1  - Pablo, Herbert
A1  - Evans, Nancy Remage
A1  - Hamaguchi, Kenji
A1  - Gull, Theodore
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Ignace, Rosina
A1  - Hoffman, Jennifer L.
A1  - Hole, Karen Tabetha
A1  - Lomax, Jamie R.
T1  - A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY, delta ORIONIS Aa. II. X-RAY VARIABILITY
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the delta Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of approximate to 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5-25 is is confirmed, with a maximum amplitude of about +/- 15% within a single approximate to 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the 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 phi = 0.0 when the secondary delta Ori Aa2 is at the 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.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: individual ([HD 36486]delta Ori A)
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/133
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
A1  - Gayley, K. G.
A1  - Hamann, Wolf-Rainer
A1  - Huenemoerder, D. P.
A1  - Ignace, R.
A1  - Pollock, A. M. T.
T1  - HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF
 WOLF-RAYET STAR WINDS
JF  - ASTROPHYSICAL JOURNAL LETTERS
N2  - We present the first high-resolutionX-ray spectrum of a putatively singleWolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, "cool" stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at approximate to 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow "sticky clumps" that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds.
KW  - stars: individual (WR 6)
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
KW  - X-rays: stars
Y1  - 2012
U6  - https://doi.org/10.1088/2041-8205/747/2/L25
SN  - 2041-8205
VL  - 747
IS  - 2
PB  - IOP PUBLISHING LTD
CY  - BRISTOL
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Corcoran, Michael F.
A1  - Moffat, Anthony F. J.
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Waldron, Wayne L.
A1  - Huenemoerder, David P.
A1  - Maiz Apellaniz, Jesus
A1  - Nichols, Joy S.
A1  - Todt, Helge Tobias
A1  - Naze, Yael
A1  - Hoffman, Jennifer L.
A1  - Pollock, Andy M. T.
A1  - Negueruela, Ignacio
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. IV. A multiwavelength, non-lte spectroscopic analysis
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system delta Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary's distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if delta Ori lies at about twice the Hipparcos distance, in the vicinity of the sigma-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be Delta V approximate to 2.(m)8. The inferred parameters suggest that the secondary is an early B-type dwarf (approximate to B1 V), while the tertiary is an early B-type subgiant (approximate to B0 IV). We find evidence for rapid turbulent velocities (similar to 200 km s(-1)) and wind inhomogeneities, partially optically thick, in the primary's wind. The bulk of the X-ray emission likely emerges from the primary's stellar wind (logL(X)/L-Bol approximate to -6.85), initiating close to the stellar surface at R-0 similar to 1.1 R-*. Accounting for clumping, the mass-loss rate of the primary is found to be log (M) over dot approximate to -6.4 (M-circle dot yr(-1))., which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual ([HD 36486]delta Ori A)
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/135
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
A1  - Huenemoerder, D. P.
A1  - Hamann, Wolf-Rainer
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Ignace, R.
A1  - Todt, Helge Tobias
A1  - Hainich, Rainer
T1  - On the Binary Nature of Massive Blue Hypergiants: High-resolution X-Ray Spectroscopy Suggests That Cyg OB2 12 is a Colliding Wind Binary
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - The blue hypergiant Cyg OB2 12 (B3Ia(+)) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si XIV and Mg XII. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions.
KW  - stars: individual (Cyg OB2 12)
KW  - stars: massive
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - supergiants
KW  - X-rays: stars
Y1  - 2017
U6  - https://doi.org/10.3847/1538-4357/aa7e79
SN  - 0004-637X
SN  - 1538-4357
VL  - 845
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -