TY  - JOUR
A1  - Huenemoerder, D.
A1  - Gayley, K.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, N.
T1  - High Resolution X-Ray Spectra of WR 6
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin"-shaped prole, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere – even at the higher energies where opacity is lowest { as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88236
SP  - 301
EP  - 304
ER  - 
TY  - JOUR
A1  - Huenemoerder, David P.
A1  - Gayley, K. G.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J. S.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, Norbert S.
A1  - Shenar, Tomer
T1  - Probing Wolf-Rayet winds: Chandra/HETG X-ray spectra of WR 6
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.
KW  - stars: individual (WR 6)
KW  - stars: massive
KW  - stars: Wolf-Rayet
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/815/1/29
SN  - 0004-637X
SN  - 1538-4357
VL  - 815
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Russell, C. M. P.
A1  - Corcoran, M. F.
A1  - Cuadra, J.
A1  - Owocki, S. P.
A1  - Wang, Q. D.
A1  - Hamaguchi, K.
A1  - Sugawara, Y.
A1  - Pollock, A. M. T.
A1  - Kallman, T. R.
T1  - Hydrodynamic and radiative transfer modeling of X-ray emission from colliding WR winds
BT  - WR 140 & the Galactic center
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray flux is tied to the orbital phase, and is a direct probe of the winds’ properties. In the Galactic center, ~30 WRs orbit the super massive black hole (SMBH) within ~10”, leading to a smorgasbord of wind-wind collisions. To model the X-ray emission of WR 140 and the Galactic center, we perform 3D hydrodynamic simulations to trace the complex gaseous flows, and then carry out 3D radiative transfer calculations to compute the variable X-ray spectra. The model WR 140 RXTE light curve matches the data well for all phases except the X-ray minimum associated with periastron, while the model spectra agree with the RXTE hardness ratio and the shape of the Suzaku observations throughout the orbit. The Galactic center model of the Chandra flux and spectral shape match well in the region r ≤ 3”, but the model flux falls off too rapidly beyond this radius.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88255
SP  - 309
EP  - 312
ER  - 
TY  - JOUR
A1  - Sugawara, Y.
A1  - Tsuboi, Y.
A1  - Maeda, Y.
A1  - Pollock, A. M. T.
A1  - Williams, P. M.
T1  - The Swift monitoring of the colliding wind binary WR 21a
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The X-ray observations of the colliding wind binary WR 21a is reported. The first monitoring performed by Swift/XRT in order to reveal the phase-locked variation. Our observations cover 201 different epochs from 2013 October 1 to 2015 January 30 for a total exposure of about 306 ks. It is found for the first time that the luminosity varies roughly in inverse proportion to the separation of the two stars before the X-ray maximum but later drops rapidly toward periastron.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88517
SP  - 366
ER  -