* Astronomy

Astronomers presented new results from the Canadian MOST (Micro variability and Oscillations of Stars) satellite at the Canadian Astronomical Society Meeting held at the Universite de Montreal.
Suzanna Randall and Prof. Gilles Fontaine, from the Universite de Montreal, announced 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.
PG 0101+039 is a subdwarf B (sdB) star at a distance of around 1000 light-years, and located in the constellation of Andromeda.
Observations uncovered three periodicities between 2600 and 7250 s attributed to intrinsic stellar pulsations, as well as an ellipsoidal deformation of the subdwarf due to its close binary status.
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 telescope designed primarily to look at much brighter objects.

Light curve (pdf)

The fact that minuscule luminosity changes with relative amplitudes as low as 0.04 % in a star of 12th magnitude exceeds the design expectations of MOST 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.
These periods are more than a factor of 10 longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying that they are due to gravity modes rather than pressure modes. The longer period pulsators are found only among cooler sdB stars, where they are surprisingly common.
While astronomers know that they are in the final stages of their long lives, the details surrounding their evolution remain somewhat mysterious.
The iron opacity instability that drive the short-period EC 14026 stars is effective only in hot sdB stars, leaving the driving mechanism for the deeper gravity modes in cool sdB stars currently unknown.
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 aster seismology.
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.
Read more (pdf)

"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. 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." - Suzanna Randall, an astronomy PhD student at the Universite de Montreal.