Welcome to Peredur Williams's home page
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
||conjunction: WC star behind
||conjunction: O star behind
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
email: pmw [at] roe.ac.uk
phone: (0) 131-668-8399