Welcome to Peredur Williams's home page



Research on Wolf-Rayet stars, especially members of colliding-wind binaries, and their carbon dust formation, X-ray and non-thermal radio emission — such as the prototype WR140, the long-period system WR48a, and the maverick Apep. 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 its orbit and colliding-wind phenomena, such as X-ray emission, and spectral line variations. Because its orbit is very elliptical (e ∼ 0.9), dust formation occurs for only a few weeks of its 7.94-year period, always at exactly the same phase.
It has become the protoype of Wolf-Rayet episodic dust makers, including WR 19 (P ∼ 10 y), WR 137 (P ∼ 13 y), WR 125 (P ∼ 28 y) in the Galaxy and HD 38030 (P ∼ 22 y) in the Large Magellanic Cloud. Related systems have been found in other galaxies.
WR 140 and WR 137 are targets of an approved JWST DD-ERS program .
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, which includes a summary of the properties of variable WR dust emitters.


Publications: links from the SAO/NASA ADS to my publications


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 at 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.

Institute for Astronomy
Royal Observatory
Blackford Hill
Edinburgh
EH9 3HJ
United Kingdom
Contact:
email: pmw [at] roe.ac.uk