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Experts in: Fundamental astronomy

Bastien, Pierre

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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BENNEKE, Björn

Professeur adjoint

The next five years present a truly unique opportunity in the history of planetary astrophysics. For the first time, the observational techniques, the theoretical models, and a sufficient number of known exoplanets orbiting nearby stars are available to spectroscopically characterize a wide diversity of planets. Planets ranging from blazingly hot giant planets to temperate Earth-sized planets in the habitable zone of their host stars.

Many unanswered questions remain: How and where do planets form? What materials make up their interiors? What gases are in their atmospheres? What role do clouds and hazes play? How big can a terrestrial planet be? How small can a gaseous planet be? And finally, what planets are capable of hosting life?

Professor Benneke’s team is currently in an exceptional position to address many of the questions above because they are currently conducting several unprecedented large observational programs using the Hubble Space Telescope, the Spitzer Space Telescope, and the 10-meter Keck observatories. They have developed powerful analysis and modeling framework to interpret these unique data sets. The main areas that Professor Benneke’s group is working on are:

  • Exploring the diversity of planetary atmospheres on super-Earths and exo-Neptunes using Hubble Space Telescope transit spectroscopy. Professor Benneke is the principal investigator of the largest Hubble Space Program in the world to characterize small exoplanets.
  • Probing the formation of giant planets using high-resolution near-infrared spectroscopy from 10-meter Keck telescopes
  • Atmospheric characterization and mapping of exoplanets using the upcoming James Webb Space Telescope (JWST)
  • Understanding the exotic cloud types on exoplanets
  • Discovery and initial characterization of prime targets for future JWST characterization using K2, TESS, and ground-based follow-up
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Bergeron, Pierre

BERGERON, Pierre

Professeur titulaire

I am interested in the study of white dwarf stars and, in particular, the calculation of model atmospheres. White dwarf stars represent the final evolutionary stage of more than 97% of stars in our galaxy, including our Sun. Having exhausted the nuclear power sources in their centre, white dwarfs cool slowly over several billion years. They have a mass comparable to that of the Sun but in a volume equal to that of the Earth, thus making them extremely compact objects whose density is a million times that of the Sun. The study of these stellar remnants and the determination of their fundamental parameters such as surface temperature, mass and chemical composition tell us not only about the nature of these stars, but also about the evolutionary link with the stars that produced them. The most accurate method for measuring the basic parameters of white dwarf stars is to compare in detail the spectroscopic data, i.e. the flux distribution as a function of wavelength, with theoretical predictions obtained from model atmospheres we have been constantly refining here at the Université de Montréal. The stellar atmosphere corresponds to the thin surface layer where the stellar radiation originates. I am also interested in the study of pulsating white dwarfs, called ZZ Ceti stars, and in particular the determination of the empirical boundaries of their instability strips. All of these theoretical projects rely on photometric and spectroscopic data obtained at different observatories at Kitt Peak in Arizona (2.3 m Steward, 2.1 m and 4 m Kitt Peak) and the Mont Mégantic Observatory.

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Doyon, René

DOYON, René

Professeur titulaire

Professor René Doyon’s research activities are focussed on the development of state-of-the-art astronomical instrumentation for various ground- and space-based observatories. He is also actively involved in various observational programs for detecting and characterizing brown dwarfs, exoplanets and young low-mass stars. On the instrumentation front, he leads several infrared instrumentation projects (camera and spectrograph) for the Observatoire du Mont-Mégantic. He is co-investigator of the Gemini Planet Imager, which has been operational since 2013.

He is also co-principal investigator of SPIRou, a high-resolution infrared spectrograph for the Canada-France-Hawaii Telescope. Scheduled for operation in 2015, SPIRou is designed to detect terrestrial (Earth-like) planets within the “habitable zone” of low-mass stars in the solar neighborhood. He is also principal investigator of NIRISS, one of the four scientific instruments on the James Webb Space Telescope.

Professor Doyon is the Director of the Institute for Research on exoplanets.

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Dufour, Patrick

DUFOUR, Patrick

Professeur agrégé

My research is oriented mainly toward the study of white dwarf atmospheres, from both the theoretical (detailed model atmosphere calculations) and observational (spectroscopic and photometric observations) viewpoints. White dwarfs are the remnants of low-mass stars that have used up their reserves of nuclear fuel. A typical white dwarf consists of a nucleus of carbon and oxygen representing over 99% of its mass, surrounded by a thin layer of helium that is itself surrounded, in about 80% of cases, by another thin layer of hydrogen. These layers, although thin, are optically opaque and regulate the rate at which the star loses energy (i.e. its cooling rate). To properly understand the evolution of white dwarfs, it is essential to understand the physical properties of these surface layers. The spectroscopic analysis of light from white dwarfs' atmospheres is the main technique used to gather information on the external parts of white dwarfs. My work is focussed on analyzing stars with traces of heavy elements (DZ and DQ spectral types) and stars with a carbon atmosphere.

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Fontaine, Gilles

FONTAINE, Gilles

Professeur titulaire

Professor Gilles Fontaine’s research in astroseismology and stellar evolution recently led him to look at the fascinating challenges involved in characterizing exoplanets, one of the most important issues in contemporary astrophysics. Most of the time, an exoplanet’s properties cannot be determined unless the fundamental characteristics of its host star are known.

The astroseismological method is an excellent tool for this purpose and, if properly used, can determine the structural parameters of a variable star with great precision, along with its internal stratification and its age. Gilles Fontaine has begun to explore this research approach, which has already proven its merits on several occasions when planets have been discovered orbiting variable stars.

An impressive and growing number of white dwarfs seem to bear signs of planetary debris, opening the possibility of determining the bulk composition of these debris, a unique tool in planetology. The potential in this case is huge and very promising. White dwarfs play the role of a “substrate,” in a way, on which heavy elements constituting planetary debris are deposited, but a permeable substrate that allows the elements to pass through at different rates.

The first step is to determine the current abundance of these heavy elements in a given white dwarf. This calls for sophisticated atmospheric models, a specialty of Gilles Fontaine young colleague Patrick Dufour. Second, these levels of abundance (which vary over time) have to be interpreted with the possible accretion rates, the effects of differential diffusion among the different elements, the presence of convection zones, thermohaline convection and other mechanisms that can partially mix external layers and ultimately extend back to the primordial composition. This is a considerable challenge, but Professor Fontaine has already begun addressing it with a major review of calculations of diffusion coefficients that he did in 1986 in co-operation with Georges Michaud at the Université de Montréal. He is counting on the collaboration of expert numerical analyst Pierre Brassard. He hopes to be soon able to effectively simulate accretion-diffusion episodes of planetary debris on white dwarfs.

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Hlavacek-Larrondo, Julie

HLAVACEK-LARRONDO, Julie

Professeure agrégée

I am an expert in the study of big black holes – those that lie at the centres of massive galaxies. I use a combination of X-ray (e.g. Chandra, XMM-Newton, Rosat), radio (e.g. JVLA, GMRT, ATCA) and optical observations (e.g. HST, VLT) for my work. The ultimate goal of my research is to provide a detailed view on the role black hole feedback plays in the formation and evolution of galaxies, from heating to metal entrainment, as well as black hole growth. Other topics I work on include observational signatures of radio halos in cluster mergers, hyper-luminours infrared galaxies, numerical simulations of jets, and compact objects in general.

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Lafrenière, David

LAFRENIÈRE, David

Professeur agrégé

The study of exoplanets aims at establishing the prevalence and diversity of planetary systems in our galaxy, understanding how these systems form and evolve, comprehending the physics involved in their atmosphere and interior and, ultimately, detecting traces of life elsewhere in the universe. This is the main interest of Professor Lafrenière's group. The group's work is primarily performed using infrared imaging techniques that allow them to detect the planets directly, and then measuring their physical properties. To successfully "see" these very faint planets located right next to their host star, which can be several million times brighter, it is necessary to continually develop new observation and image processing techniques and even to build new instruments. With current technology, it is possible to detect gas giant planets with orbits of the outer solar system's size or larger.

In addition to direct imaging of planets, Professor Lafrenière's research group is also interested in the characterization of "hot Jupiter" planets by using transit/eclipse spectrophotometry and transit timing. The group is also involved in studies of brown dwarfs, in stellar and substellar multiplicity studies, and in searching for new young low-mass stars in the solar neighborhood.

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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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