The orbit and distance of WR140

TL;DR

This study uses high-resolution radio observations and IR data to determine the orbit and distance of the WR140 binary system, revealing the wind-collision region's rotation and constraining key orbital parameters.

Contribution

First detailed VLBA and IR interferometry combined analysis to determine WR140's orbit inclination, orientation, and distance with high precision.

Findings

Orbit inclination: 120° ± 4°

Distance to WR140: 1.81 ± 0.08 kpc

WCR rotation consistent with orbital motion

Abstract

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 \pm 4 \degree, the longitude of the ascending node as 352\degree \pm 2 \degree, and the orbit semimajor axis as 9.0 \pm 0.1 mas. This leads to a distance estimate to WR140 of 1.81 \pm 0.08 kpc. Further refinements of the orbit and distance await more IR interferometric observations of the stellar components directly.