TY  - JOUR
A1  - Ramiaramanantsoa, Tahina
A1  - Moffat, Anthony F. J.
A1  - Harmon, Robert
A1  - Ignace, R.
A1  - St-Louis, Nicole
A1  - Vanbeveren, Dany
A1  - Shenar, Tomer
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Howarth, Ian D.
A1  - Stevens, Ian R.
A1  - Piaulet, Caroline
A1  - St-Jean, Lucas
A1  - Eversberg, Thomas
A1  - Pigulski, Andrzej
A1  - Popowicz, Adam
A1  - Kuschnig, Rainer
A1  - Zoclonska, Elzbieta
A1  - Buysschaert, Bram
A1  - Handler, Gerald
A1  - Weiss, Werner W.
A1  - Wade, Gregg A.
A1  - Rucinski, Slavek M.
A1  - Zwintz, Konstanze
A1  - Luckas, Paul
A1  - Heathcote, Bernard
A1  - Cacella, Paulo
A1  - Powles, Jonathan
A1  - Locke, Malcolm
A1  - Bohlsen, Terry
A1  - Chené, André-Nicolas
A1  - Miszalski, Brent
A1  - Waldron, Wayne L.
A1  - Kotze, Marissa M.
A1  - Kotze, Enrico J.
A1  - Böhm, Torsten
T1  - BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant zeta Puppis unveils the photospheric drivers of its small- and large-scale wind structures
JF  - Monthly notices of the Royal Astronomical Society
N2  - From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He ii λ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He ii λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.
KW  - techniques: photometric
KW  - techniques: spectroscopic
KW  - stars: massive
KW  - stars: rotation
KW  - starspots
KW  - supergiants
KW  - stars: winds, outflows
Y1  - 2017
U6  - https://doi.org/10.1093/mnras/stx2671
SN  - 0035-8711
SN  - 1365-2966
VL  - 473
IS  - 4
SP  - 5532
EP  - 5569
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - CHAP
A1  - Cassinelli, Joseph P.
A1  - Ignace, R.
A1  - Waldron, W.
A1  - Cho, J.
A1  - Murphy, N.
A1  - Lazarian, A.
T1  - X-ray line emission produced in clump bow shocks
N2  - We summarize Chandra observations of the emission line profiles from 17 OB stars. The lines tend to be broad and unshifted. The forbidden/intercombination line ratios arising from Helium-like ions provide radial distance information for the X-ray emission sources, while the H-like to He-like line ratios provide X-ray temperatures, and thus also source temperature versus radius distributions. OB stars usually show power law differential emission measure distributions versus temperature. In models of bow shocks, we find a power law differential emission measure, a wide range of ion stages, and the bow shock flow around the clumps provides transverse velocities comparable to HWHM values. We find that the bow shock results for the line profile properties, consistent with the observations of X-ray line emission for a broad range of OB star properties.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18057
ER  - 
TY  - JOUR
A1  - Richardson, Noel D.
A1  - Russell, Christopher M. P.
A1  - St-Jean, Lucas
A1  - Moffat, Anthony F. J.
A1  - St-Louis, Nicole
A1  - Shenar, Tomer
A1  - Pablo, Herbert
A1  - Hill, Grant M.
A1  - Ramiaramanantsoa, Tahina
A1  - Corcoran, Michael
A1  - Hamuguchi, Kenji
A1  - Eversberg, Thomas
A1  - Miszalski, Brent
A1  - Chene, Andre-Nicolas
A1  - Waldron, Wayne
A1  - Kotze, Enrico J.
A1  - Kotze, Marissa M.
A1  - Luckas, Paul
A1  - Cacella, Paulo
A1  - Heathcote, Bernard
A1  - Powles, Jonathan
A1  - Bohlsen, Terry
A1  - Locke, Malcolm
A1  - Handler, Gerald
A1  - Kuschnig, Rainer
A1  - Pigulski, Andrzej
A1  - Popowicz, Adam
A1  - Wade, Gregg A.
A1  - Weiss, Werner W.
T1  - The variability of the BRITE-est Wolf-Rayet binary, gamma(2) Velorum-I. Photometric and spectroscopic evidence for colliding winds
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report on the first multi-colour precision light curve of the bright Wolf-Rayet binary gamma(2) Velorum, obtained over six months with the nanosatellites in the BRITE-Constellation fleet. In parallel, we obtained 488 high-resolution optical spectra of the system. In this first report on the data sets, we revise the spectroscopic orbit and report on the bulk properties of the colliding winds. We find a dependence of both the light curve and excess emission properties that scales with the inverse of the binary separation. When analysing the spectroscopic properties in combination with the photometry, we find that the phase dependence is caused only by excess emission in the lines, and not from a changing continuum. We also detect a narrow, high-velocity absorption component from the He perpendicular to lambda 5876 transition, which appears twice in the orbit. We calculate smoothed-particle hydrodynamical simulations of the colliding winds and can accurately associate the absorption from He perpendicular to to the leading and trailing arms of the wind shock cone passing tangentially through our line of sight. The simulations also explain the general strength and kinematics of the emission excess observed in wind lines such as C III lambda 5696 of the system. These results represent the first in a series of investigations into the winds and properties of gamma(2) Velorum through multi-technique and multi-wavelength observational campaigns.
KW  - stars: early type
KW  - stars: individual: gamma(2) Vel
KW  - stars: mass loss
KW  - stars: winds
KW  - outflows
KW  - stars: Wolf-Rayet
Y1  - 2017
U6  - https://doi.org/10.1093/mnras/stx1731
SN  - 0035-8711
SN  - 1365-2966
VL  - 471
SP  - 2715
EP  - 2729
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Parkin, E. R.
A1  - Broos, Patrick  S.
A1  - Townsley, L. K.
A1  - Pittard, J. M.
A1  - Moffat, Anthony F. J.
A1  - Naze, Y.
A1  - Rauw, G.
A1  - Oskinova, Lida
A1  - Waldron, W. L.
T1  - X-RAY EMISSION FROM THE DOUBLE-BINARY OB-STAR SYSTEM QZ CAR (HD 93206)
JF  - ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
N2  - X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P-A = 21 days) and B (O8 III+o9 v, P-B = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT similar or equal to 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of similar or equal to 0.2 x 10(22) cm(-2). Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of similar or equal to 7x10(-13) erg s(-1) cm(-2), do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III+o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B.
KW  - hydrodynamics
KW  - stars: early-type
KW  - stars: individual (QZ Carinae)
KW  - stars: massive
KW  - stars: winds, outflows
KW  - X-rays: stars
Y1  - 2011
U6  - https://doi.org/10.1088/0067-0049/194/1/8
SN  - 0067-0049
VL  - 194
IS  - 1
PB  - IOP PUBLISHING LTD
CY  - BRISTOL
ER  -