Professor of Astronomy and Astrophysics
University of Toronto
4035 Davis Building
University of Toronto Mississauga (UTM)
3359 Mississauga Road N.
L5L 1C6, Canada
john.lester AT utoronto.ca
lester AT astro.utoronto.ca
Undergraduate Teaching in 2016-2017
- AST 101 (UTM) - Solar System Astronomy
- AST 110 (UTM) - Introduction to Astronomical Observations
Graduate Teaching in 2016-2017
Almost of the natural light we see, night and day, was emitted by the
surface atmospheric layers of stars. Although the stellar atmosphere is
a spatially very thin layer, it is important for several reasons:
My approach to studying the physics of stellar atmospheres is to
concentrate on the bright stars that can be observed in the greatest
detail, and to interpret those observations using computer models.
- the physical conditions are changing extremely rapidly from the
hot, dense stellar interior and to the near vacuum of space
- the physical processes are still poorly understood because
terrestrial labs are tiny compared to the scale of a stellar
atmosphere with its variation of temperature, pressure, velocity
and magnetic field
- the stellar atmosphere has the great advantage of being directly
Current Research Opportunities
Until recently, the Sun was the only star whose surface could be
observed. Now, thanks to the technique of optical/infrared
interferometry, we can observe the surfaces of some of the nearer stars.
This is a revolutionary breakthrough that is opening up many exciting
new opportunities to understand individual stars.
Stars are characterized by three fundamental physical parameters -
luminosity, mass and radius - in addition to their chemical composition.
We can determine a star's radius by combining measurements of the
star's distance and angular diameter (measured using interferometry).
Knowing the radius, we can determine the luminosity from measuring the
star's apparent brightness and distance. However, both radius and
luminosity are functions of the star's mass, which is not directly
observable for a single star.
We are studying if we can derive the mass of a non-binary star by
comparing the observed surface brightness distribution of the star,
determined by several methods, with the intensities predicted using a
spherical stellar atmosphere. Our initial concentration is on red
giants and red supergiants, but we are also working toward applying
our approach to some of the radially pulsating stars, such as Cepheids.
Model Atmosphere Programs
Last updated: 2015 May 22