CANADIAN SPACE TELESCOPE DETECTS PUZZLING BRIGHTNESS VARIATIONS IN DYING STAR

Astronomers are today presenting new results from the Canadian MOST (‘Microvariability and Oscillations of STars’) satellite at the Canadian Astronomical Society Meeting held at the Université de Montréal. Suzanna Randall and Prof. Gilles Fontaine from the Université de Montréal will announce the detection of brightness variations (“pulsations”) in the small ageing star PG 0101+039 in collaboration with Prof. Jaymie Matthews, Jason Rowe and Dr. Rainer Kuschnig (University of British Columbia) and the international MOST Science Team. The confirmed variability of this star is of particular interest because it violates predictions of stellar pulsation and will force a thorough reconsideration of current theory.

PG 0101+039 is a subdwarf B star located in the constellation of Andromeda at a distance of around 1000 light-years. Its brightness fluctuations were observed for nearly 17 consecutive days starting on 28 September 2004 with MOST, Canada’s first orbiting space telescope. Around 250 times less bright than the dimmest star visible with the naked eye, this star is relatively faint for the 15-cm (5.9-inch) telescope designed primarily to look at much brighter objects. The fact that minuscule luminosity changes of less than 1 % of the star’s normal brightness were nevertheless detected constitutes a significant achievement and holds great promise for the future space-based exploration of subdwarf B stars.

Subdwarf B stars are around 5 times hotter than our Sun, and so dense that - at comparable masses - they are about 10 times smaller. They are rather abundant in the night-time sky and dominate the population of bright blue stars. While astronomers know that they are in the final stages of their long lives, the details surrounding their evolution remain somewhat mysterious. Following the discovery of pulsating subdwarf B stars, it is now hoped that evolutionary theories can be constrained through the use of a technique called asteroseismology. Analogous to seismology on Earth, asteroseismology is essentially the study of ‘starquakes’, seeking to match the brightness variations observed in a star to those predicted for a particular model and thus determine its temperature, size and chemical composition. “Asteroseismology lets us probe deep inside stars to reveal their internal composition, an aspect that normally remains hidden even from the world’s largest telescopes” explains Suzanna Randall, an astronomy PhD student at the Université de Montréal, “The asteroseismological potential of pulsating subdwarf B stars in particular may hold the key to a more mature comprehension of the evolution, life and death of stars. While the detection of oscillations in PG 0101+039 challenges our current models, it will ultimately lead to a better understanding of these valuable objects.”

The MOST mission was financed by the Canadian Space Agency and supported by the Natural Sciences and Engineering Research Council of Canada.

For more Information:

Suzanna Randall
Phone: 514-343-6111 ext. 3797
Email: randall@astro.umontreal.ca

Prof. Gilles Fontaine
Phone: 514-343-6680
Email: fontaine@astro.umontreal.ca

Figure caption :
Full MOST lightcurve obtained for the subdwarf B star PG 0101+039 over 16.9 days starting 28 September 2004. Each data point corresponds to the relative brightness of the star at that particular time. The top row covers the first 24-hour period of the run, and the data for subsequent days have been shifted downwards arbitrarily for visualisation purposes. This material was presented to the Canadian Astronomical Society meeting in Montreal, QC on May 15, 2005. CREDIT: Université de Montréal and MOST.

EDITORS: This image can be obtained over the Internet via
http://www.astro.umontreal.ca/~randall/Astronomy/MOST/MOSTlightcurve.pdf
http://www.astro.umontreal.ca/~randall/Astronomy/MOST/MOSTlightcurve.eps