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/ Department of Physics

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Experts in: Polarimetry

Bastien, Pierre


Professeur associé

My research deals mostly with star and planetary system formation. This is one of the priority research areas identified by the Canadian astronomical community. For this research, I mainly use light polarization as a means of gathering data.

Here are two examples of my ongoing research projects:

  1. Natural light vibrates in a plane that varies continuously and at random. When it vibrates in a preferential plane, we say that it is polarized. For measuring polarization from celestial objects, I am supervising a new polarimeter being built for the Mont Mégantic Observatory, POMM, that will be 100 times more precise than the one currently in use. Light from a young star is scattered and polarized by microscopic dust grains. By measuring this polarization, we can learn more about the properties of the grains and the distribution of matter around young stars or with disks of debris. Combining these data with other observations and with modelling, we learn about conditions in protoplanetary disks where planets are formed. I will also be observing stars with exoplanets to learn about the properties of the atmospheres of these planets and determine the inclination of their orbits.
  2. I also built a polarimeter, POL-2, for the James-Clerk-Maxwell radiotelescope on Mauna Kea in Hawaii. It will soon give us information about magnetic fields in dense molecular clouds and star formation processes. We want to find out if magnetic fields are more important than turbulence (or vice versa) in slowing star formation processes, because observations show us that they are slower than what our models predict.

Areas of expertise

  • Star formation
  • Polarimetry
  • Young stars

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St-Louis, Nicole

ST-LOUIS, Nicole

Directrice de département, 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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