A doctoral student at Armagh Observatory is searching for rare but important magnetic stars that may help explain how stars form, writes Dick Ahlstrom
ASTRONOMY IS A science without borders, in its subject matter and in its practice. The universe doesn't have edges and space seems to continue without limit. And the scientists who study celestial phenomena are not restricted by nationality or by the source of the data they study.
Colin Folsom is a case in point. A Canadian from Kingstown, Ontario, he is working on a PhD at Armagh Observatory using data acquired by telescopes in Hawaii and Chile.
He is interested in binary starts, particularly those that display powerful magnetic fields. His goal is to explain how these stars acquired their magnetic fields and how having the field affects the star's long term development.
Folsom is one of a number of young PhD candidates who will present their research tomorrow in Armagh at the spring meeting of the Astronomical Science Group of Ireland (ASGI).
Founded in 1974 to foster scientific collaboration between astronomers in all parts of Ireland, ASGI is one of the oldest cross-Border bodies on the island. It holds spring and autumn meetings at which researchers present their latest work.
This year will also see a keynote address by Prof Janet Drew of the University of Hertfordshire's Centre for Astrophysics Research. She is one of three leaders with Paul Groot in The Netherlands, and Antonio Mampaso in Spain of IPHAS, an international survey of the stars in our Milky Way galaxy.
Folsom is interested in a small helping of those stars, comparatively young stars that have their own magnetic field. He looks in particular at young binary stars, paired twins. "A binary star is two stars orbiting around each other," he says. "I am interested in two stars of equal mass. Binaries are actually pretty common. They make up something like half the stars in the sky."
Folsom came to Armagh after completing a MSc in Canada. "I was getting interested in the young-star stuff and a guy I was working with in Kingston knew one of the astronomers in Armagh." He got in touch with the observatory and was accepted as a PhD student working under supervisor, Dr Stefano Dagnulo.
Folsom wants to learn more about magnetic stars. "Why do some of these stars have big magnetic fields and other have no magnetic field and how does this affect the star and how it evolves over time," he says.
"In relatively small stars like our sun we feel we have a handle on what is going on to produce a magnetic field," he explains. It is believed to be similar to the magnetic field produced by the earth's core, caused by the movement of a partially liquid core. "In a star like our sun we think it is the same thing, material moving around in the core.
"In the stars I am looking at, the feeling is there shouldn't be material like this moving inside. Rather than the magnetic field being generated by material moving around, it is actually frozen into the star."
He focuses on stars with masses two to four times that of our sun, and can detect whether either of the binary pair has a magnetic field by studying the star's light spectrum.
"We can see the magnetic field if we look at the spectrum of the star splitting up its light. You have to have relatively good resolution to see the effect we are talking about," he says.
Finding magnetic stars is no simple matter however. "There are only a handful of cases where we find a magnetic star in a binary but we haven't been looking for very long," Folsom says. They have no example where both stars in a binary pair are magnetic, and in a given 100 stars just 5 per cent to 10 per cent might have magnetic fields of varying strengths. Once found he tries to characterise the magnetic field and seeks to answer two key questions, the origins of the field and whether it affected the accretion of material that ultimately formed the star.
"When the star is still forming we would expect the magnetic field would affect the way material gets added to it," he explains. The field may also affect how long the star lasts before reaching the end of its days.
More information about IPHAS is available from www.iphas.org