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Experts in: Spectroscopy and spectrophotometry

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


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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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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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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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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