Astrophysics

Forty days of observation from space

For 40 days and nights between mid-June and the end of July, 2004, a Université de Montréal team was able to observe a star located close to the constellation of Aquila. The observations could furnish vital information about the death of massive stars. “The star we observed originally had a mass 20 times the Sun’s mass. But when a star this size dies, it quickly sheds matter, and the unprecedented observations we were able to make will enable us to determine its age.”

The star observed by Professor Moffat’s team, called WR 123, is a Wolf-Rayet type star, and was described for the first time by Professor Moffat in the 1970s. Given the distance to the star, observing it was always problematic. However, since last year, researchers have been able to use a new Canadian space observatory. The MOST satellite (its name an abbreviation of Microvariability and Oscillations of Stars) might best be described as a little brother to the Hubble telescope. The small observatory, the size of a suitcase and weighing 60 kilograms, orbits the earth every 100 minutes, crossing both poles. To keep costs down, the observatory was launched not from the United States or Europe, but from the Plesetsk Cosmodrome in northern Russia, on June 20th, 2003. The launch and operation went off without a hitch.

Tony Moffat, along with other Canadian researchers, has become deeply involved in this highly original project. It cost about $10 million, a fraction what Hubble cost. In an orbit 820 km above the earth’s surface, the observatory has a mirror that is hardly bigger than a plate, but is capable of high precision observations. “I have always been very intrigued by new technologies, and this has been a great success given its cost and the benefits for research in Canada,” explains the professor.

MOST has already resulted in the publication of a letter to Nature in July, 2004. Authored by Jaymie Matthews and co-authored by Anthony Moffat, the article reports observations of Procyon, a star similar to the Sun. “MOST is currently the only instrument capable of obtaining high-precision photometric information (a few parts in a million) in stars other than the Sun,” write the authors. Following his summer observations, Tony Moffat hopes to be able to determine the age of WR 123 by analyzing variations of the radiation emitted. Even though the star is 20,000 light-years away, it emits enough light to allow the researchers to determine its nature due to the fact that young stars contain more hydrogen than helium. Sound waves can thus travel through hydrogen faster than through helium, which is heavier. These waves create pulsations at the surface of the stars, which then changes the intensity of the emitted light. The MOST instruments can measure these intensity variations, which can then be used to estimate the age of a star. “The observations done this summer have given us voluminous data on the star’s variations. We will look at each and every minute detail in order to find the slightest variation,” proclaims the astrophysicist.