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, the long-period system WR48a, and the maverick Apep. Colliding wind binary logo
More dust-making Wolf-Rayet stars, some variable or episodic and ten apparently constant dust makers, have been identified in a study of NEOWISE-R survey observations.

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 late 2016, stimulating an on-going intensive multi-wavelength observing campaign to study colliding-wind phenomena. It is the prime target of an approved JWST DD-ERS program .
Some results from the observing campaign to cover the previous (2009) periastron were reported in July 2010 at the 39th Liège International Astrophysical Colloquium "The multi-wavelength view of Hot Massive Stars"
Dates of critical configurations based on the 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 and 2024-25

phase MJD Year Date Orbital phenomenon f r/a P.A. pos ψ MJD Year Date
0.9551 57610 2016.62 Aug 10 conjunction: WC star behind 223 0.56 84 E 30 60506 2024.54 July 15
0.9965 57730 2016.94 Dec 8 quadrature 313 0.12 354 N 90 60626 2024.86 Nov 12
0.000 57740 2016.96 Dec 18 periastron passage 0 0.10 327 NW 129 60637 2024.89 Nov 23
0.0032 57749 2016.99 Dec 27 conjunction: O star behind 42 0.12 263 W 150 60645 2024.91 Dec 1
0.0393 57855 2017.28 April 11 quadrature 133 0.51 174 S 90 60751 2025.21 Mar 17

I am studying the third Astronomer Royal for Scotland, Ralph Copeland (1837-1905). He lived an adventurous early life, leaving England to join the Australian gold rush when he was 15 and then worked on a sheep farm. He returned to Britain, worked as a locomotive engineer and then went to the University of Göttingen, where he gained a PhD. He participated in the Second German North Polar expedition, working on a preliminary geodetic survey, and adding to the food supply with his rifle. On his return, he took positions in Ireland, first at Lord Rosse's observatory at Birr Castle and then at Dunsink. From 1876-1888, he worked at Lord Crawford's observatory at Dun Echt, Aberdeenshire. During this time, he made an expedition to study observing conditions in South America, making observations at Puno on Lake Titicaca and Vincocaya (elev. 14,360 ft). In 1889, he was appointed Astronomer Royal for Scotland in succession to Charles Piazzi Smyth and played a major part in moving the Royal Observatory from Calton Hill to Blackford Hill. There is a small bibliography here.

Publications: links from the SAO/NASA ADS to most of my publications, together with some interlopers (still to be fixed!)

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

2. Fuller bibliography (ordered by date)

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

phone: (0) 131-668-8399