Welcome to Peredur Williams's home page

Research on Wolf-Rayet stars and colliding-wind binaries, especially carbon dust formation, X-ray and non-thermal radio emission from systems such as the prototype WR140 and WR48a. Colliding wind binary logo

The most massive hot stars are constantly losing mass in fast (1000-3000 km s-1) stellar winds which carry away ∼ 10-6 to 10-5 M y-1 (the higher mass loss coming from Wolf-Rayet stars), giving the winds significant kinetic power. When the stars are members of binary systems, "colliding-wind binaries", the winds crash into each other between the stars and some of this power is dissipated, leading to shocks, heating of the winds, strong X-ray emission, particle acceleration and sometimes even the formation of clouds of carbon dust if one of the stars is a WC-type Wolf-Rayet star.
If the two stars are in an elliptical orbit, the strength of the wind collision will vary round the orbit, being most intense when the stars are closest, i.e. during periastron passage. The most recent periastron passage in the prototype, WR 140 (= HD 193793), occurred in early 2009, stimulating an intensive multi-wavelength observing campaign to study colliding-wind phenomena. Some results from the campaign were reported in July 2010 at the 39th Liège International Astrophysical Colloquium "The multi-wavelength view of Hot Massive Stars"
The next periastron passage is due at the end of 2016 and observing time is already being sought to study the system as its configuration changes rapidly on account of the high orbital eccentricity. Dates of critical configurations based on the definitive orbit are given below, where f is the true anomaly, ψ is the angle between our line of sight and the axis joining the WC7 and O5 stars (which would be the axis of symmetry of the wind-collision region in the absence of orbital motion), P.A. is the position angle of this axis on the sky and r/a is the separation of the stars.

Critical configurations of WR 140 in 2016-17

phase MJD Year Date Orbital phenomenon f r/a P.A. pos ψ
0.9551 57610 2016.62 Aug 10 conjunction: WC star behind 223 0.56 84 E 30
0.9965 57730 2016.94 Dec 8 quadrature 313 0.12 354 N 90
0.000 57740 2016.96 Dec 18 periastron passage 0 0.10 327 NW 129
0.0032 57749 2016.99 Dec 27 conjunction: O star behind 42 0.12 263 W 150
0.0393 57855 2017.28 April 11 quadrature 133 0.51 174 S 90

Expected IR magnitudes of WR 140 for planning observations

Phase 0.995 0.02 0.04 0.06 0.08 0.10
Date 2016 Dec 4 2017 Feb 14 April 13 June 10 August 7 Oct 4
K 5.12 3.45 3.89 4.12 4.42 4.60
L' 4.81 2.25 2.43 2.45 2.81 2.90

Publications: links from the SAO/NASA ADS to most of my publications, together with a few interlopers

1. Select bibliography (First-author papers, ordered by citation score)

2. Fuller bibliography (All sorts, ordered by date, from most recent)

Institute for Astronomy
Royal Observatory
Blackford Hill
United Kingdom
email: pmw [at] roe.ac.uk

phone: (0) 131-668-8399