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Post Info TOPIC: Collision of Powerful Stellar Winds:
Blobrana


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WR 140
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Title: The X-ray Lightcurve of WR 140
Authors: M. F. Corcoran, A. M. T. Pollock, K. Hamaguchi, C. Russell

WR 140 is a canonical massive "colliding wind" binary system in which periodically-varying X-ray emission is produced by the collision between the wind of the WC7 and O4-5 star components in the space between the two stars. We have obtained X-ray observations using the RXTE satellite observatory through almost one complete orbital cycle including two consecutive periastron passages. We discuss the results of this observing campaign, and the implications of the X-ray data for our understanding of the orbital dynamics and the stellar mass loss.

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Blobrana


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Title: WR 140 in the Infrared
Authors: Peredur Williams

Observations in the infrared have played a significant role in the development of our understanding of WR140. Two sets of observations are described here: the changing profile of the 1.083-{\mu}m He I line observed for the 2009 campaign to study evolution of the wind-collision region near periastron passage, and multiwavelength photometry and imaging of the dust made by WR140 in previous periastron passages.

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Blobrana


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Posts: 131433
Date:
WR140
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Title: The Orbit and Distance of WR140 - Proceedings of "Stellar Winds in Interaction" 2010
Authors: S.M. Dougherty, V. Trenton, A.J. Beasley

A campaign of 35 epochs of milli-arcsec resolution VLBA observations of the archetype collidingwind WR+O star binary system WR140 show the wind-collision region (WCR) as a bow-shaped arc of emission that rotates as the highly eccentric orbit progresses. The observations comprise 21 epochs from the 1993- 2001 orbit, discussed by Dougherty et al. (2005), and 14 epochs from the 2001-2009 orbit, and span orbital phase 0.43 to 0.95. Assuming the WCR is symmetric about the line-of-centres of the two stars and "points" at the WR star, this rotation shows the O star moving from SE to E of the WR star between these orbital phases. Using IR interferometry observations from IOTA that resolve both stellar components at phase 0.297 in conjunction with orbital parameters derived from radial velocity variations, the VLBA observations constrain the inclination of the orbit plane as 120°±4°, the longitude of the ascending node as 352°±2°, and the orbit semimajor axis as 9.0±0.1 mas. This leads to a distance estimate to WR140 of 1.81±0.08 kpc. Further refinements of the orbit and distance await more IR interferometric observations of the stellar components directly.

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Blobrana


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Posts: 131433
Date:
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Title: The orbit and distance of WR140
Authors: S.M. Dougherty, V. Trenton, A.J. Beasley

A campaign of 35 epochs of milli-arcsecond resolution VLBA observations of the archetype colliding wind WR+O star binary system WR140 show the wind-collision region (WCR) as a bow-shaped arc of emission that rotates as the highly eccentric orbit progresses. The observations comprise 21 epochs from the 1993-2001 orbit, discussed by Dougherty et al. (2005), and 14 epochs from the 2001-2009 orbit, and span orbital phase 0.43 to 0.95. Assuming the WCR is symmetric about the line-of-centres of the two stars and "points" at the WR star, this rotation shows the O star moving from SE to E of the WR star between these orbital phases. Using IR interferometry observations from IOTA that resolve both stellar components at phase 0.297, in conjuction with orbital parameters derived from radial velocity variations, the VLBA observations constrain the inclination of the orbit plane as 120\degree ±4 \degree, the longitude of the ascending node as 352\degree ±2 \degree, and the orbit semimajor axis as 9.0 ±0.1 mas. This leads to a distance estimate to WR140 of 1.81 ±0.08 kpc. Further refinements of the orbit and distance await more IR interferometric observations of the stellar components directly.

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Blobrana


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Posts: 131433
Date:
Collision of Powerful Stellar Winds:
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Astronomers have spotted a binary star system that could collapse to produce a massive gamma-ray burst at any point during the next few hundred thousand years and it is pointing at Earth.
The binary star system WR 104, some 8,000 light-years from Earth in the Sagittarius constellation, is made up of two stars that complete an orbit of one another every 8 months. Both stars are massive and have strong solar winds that spew out material, resulting in a spiralling trail of hot gas and dust.

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Blobrana


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Posts: 131433
Date:
WR 104
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Title: The prototype colliding-wind pinwheel WR 104
Authors: Peter Tuthill, John Monnier, Nicholas Lawrance, William Danchi, Stan Owocki, Kenneth Gayley

Results from the most extensive study of the time-evolving dust structure around the prototype "Pinwheel" nebula WR 104 are presented. Encompassing 11 epochs in three near-infrared filter bandpasses, a homogeneous imaging data set spanning more than 6 years (or 10 orbits) is presented. Data were obtained from the highly successful Keck Aperture Masking Experiment, which can recover high fidelity images at extremely high angular resolutions, revealing the geometry of the plume with unprecedented precision. Inferred properties for the (unresolved) underlying binary and wind system are orbital period 241.5 ± 0.5 days and angular outflow velocity of 0.28 ± 0.02 mas/day. An optically thin cavity of angular size 13.3 ± 1.4 mas was found to lie between the central binary and the onset of the spiral dust plume. Rotational motion of the wind system induced by the binary orbit is found to have important ramifications: entanglement of the winds results in strong shock activity far downstream from the nose of the bowshock. The far greater fraction of the winds participating in the collision may play a key role in gas compression and the nucleation of dust at large radii from the central binary and shock stagnation point. Investigation of the effects of radiative braking pointed towards significant modifications of the simple hydrostatic colliding wind geometry, extending the relevance of this phenomena to wider binary systems than previously considered. Limits placed on the maximum allowed orbital eccentricity of e < 0.06 argue strongly for a prehistory of tidal circularisation in this system. Finally we discuss the implications of Earth's polar (i < 16 deg) vantage point onto a system likely to host supernova explosions at future epochs.

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Blobrana


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Posts: 131433
Date:
Dusty Wolf-Rayet Stars
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Title: The Keck Aperture Masking Experiment: Near-Infrared Sizes of Dusty Wolf-Rayet Stars
Authors: J. D. Monnier (1) P. G. Tuthill (2), W. C. Danchi (3), N. Murphy (1,4), T. J. Harries (5) ((1) University of Michigan, Astronomy, (2) University of Sydney, (3) NASA-Goddard, (4) University of Wisconsin, (5) University of Exeter)

We report the results of a high angular resolution near-infrared survey of dusty Wolf-Rayet stars using the Keck-1 Telescope, including new multi-wavelength images of the pinwheel nebulae WR 98a, WR 104, and WR 112. Angular sizes were measured for an additional 8 dusty WR stars using aperture masking interferometry, allowing us to probe characteristics sizes down to ~20 milliarcseconds (~40 AU for typical sources). With angular sizes and specific fluxes, we can directly measure the wavelength-dependent surface brightness and size relations for our sample. We discovered tight correlations of these properties within our sample which could not be explained by simple spherically-symmetric dust shells or even the more realistic ''pinwheel nebula'' (3-D) radiative transfer model, when using optical constants of Zubko. While the tightly-correlated surface brightness relations we uncovered offer compelling indirect evidence of a shared and distinctive dust shell geometry amongst our sample, long-baseline interferometers should target the marginally-resolved objects in our sample in order to conclusively establish the presence or absence of the putative underlying colliding wind binaries thought to produce the dust shells around WC Wolf-Rayets.

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Blobrana


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Posts: 131433
Date:
Collision of Powerful Stellar Winds:
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Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have tracked the motion of a violent region where the powerful winds of two giant Wolf-Rayet stars slam into each other.
The collision region moves as the stars, part of a binary pair, orbit each other, and the precise measurement of its motion was the key to unlocking vital new information about the stars and their winds.

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Both stars are much more massive than the Sun -- one about 20 times the mass of the Sun and the other about 50 times the Sun's mass. Wolf-Rayet stars are characterized by a very strong wind of particles propelled outward from its surface. The more massive star also has a strong outward wind, but one less intense than that of the Wolf-Rayet star. The two stars, part of a system named WR 140, circle each other in an elliptical orbit roughly the size of our Solar System in an orbital cycle of 7.9 years.
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Orbital animation (.gif)


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