* Astronomy

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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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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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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