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Experts in: Mass loss and stellar winds

MOFFAT, Anthony F. J.

Professeur émérite

Massive stars comprise all those with an initial mass exceeding 8 solar masses, and which collapse upon themselves as supernovae at the end of their nuclear "burning" lives, leaving neutron stars or black holes. Since the light produced by a normal star is roughly equivalent to the cube of its mass, a single star of 100 solar masses can emit the equivalent of one million suns. Beyond 20 solar masses, massive stars are distinguished by their strong winds, which can be up to one billion times stronger than that of our Sun, which we already consider quite strong (comets, auroras, etc.). Although they are rare and short-lived, massive stars emit enormous amounts of radiation, most of it in deadly ultraviolet, and matter enriched with heavy elements, into the interstellar environment, ready to form even more generations of stars and planets such as Earth. This process was especially important early in the life of the Universe, when the very first stars were forming, all of them very massive. My research is aimed mainly at exploring: (1) whether the pressure of radiation alone is enough to accelerate the extreme winds of pre-supernova stars, i.e. during the He-burning phase as Wolf-Rayet stars, using the first Canadian spatial telescope on the MOST microsatellite, (2) building a system of microsatellites (BRITE-Constellation) to examine the very low variability of a large sample of luminous stars, (3) how exactly winds accelerate around luminous, hot stars, (4) the role of magnetic fields in accelerating their winds, (5) the mystery of how dust forms and survives in the hostile environment of luminous, hot stars, (6) the upper limit for the most massive stars (100, 150 or 200 solar masses in the current Universe?), (7) the number of WR stars in our entire Galaxy, most of them hidden by interstellar dust, and (8) whether WR stars really do explode into supernovas, leading in some cases to the most energetic (albeit short-lived) phenomenon in the Universe, gamma ray bursts.

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St-Louis, Nicole

ST-LOUIS, Nicole

Professeure titulaire

My research is mainly on the wind from the most massive stars. In view of their great luminosity - reaching one million times that of the Sun - these stars lose a large proportion of their mass over their lifetimes. This stellar wind is not symmetrical or homogenous. Not only does it contain small-scale inhomogeneities relating to turbulence, but in some cases also large-scale structures. These structures are particularly intriguing, since they are created by an as-yet unidentified mechanism occurring at the surface of the star.

The possible mechanisms include magnetic fields and pulses, two important physical processes in the evolution of massive stars, but about which we still have very little information.

The consequences of these large-scale structures for observable data (spectrum, photometry, polarization rate) can also help us to determine a fundamental parameter of these stars: their rotation velocity. This important detail is usually impossible to measure for the massive stars I am studying, since their surface is completely concealed behind the very dense wind. Because the large-scale structures are attached to the surface, identifying a period in the star's spectral or luminous variations lets us deduce the rotation velocity.

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