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 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 campaign for 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 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


In a search for more variable or episodic dust making WR stars, I am collecting 3.6-μm photometry from the reactivated NEOWISE Mission for all accesible WC stars. So far, 15 new WR dust makers have been found, eight variable. Preliminary results were presented at the 2018 EWASS meeting.
I am studying the third Astronomer Royal for Scotland, Ralph Copeland (1837-1905). He lived an adventurous early life, joining the Australian gold rush when he was 18 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, and then took positions in Ireland at Lord Rosse's observatory at Birr Castle and then 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. In 1889, he was appointed Astronomer Royal for Scotland and played a major part in moving the 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 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
Edinburgh
EH9 3HJ
United Kingdom
Contact:
email: pmw [at] roe.ac.uk

phone: (0) 131-668-8399