John Lester's Homepage

	John Lester Professor of Astronomy and Astrophysics University of Toronto
	Address:	4035 Davis Building University of Toronto Mississauga (UTM) 3359 Mississauga Road N. Mississauga, Ontario L5L 1C6, Canada
	E-mail:	`john.lester` AT `utoronto.ca` or `lester` AT `astro.utoronto.ca`
	Office Telephone:	(905) 828-3818

Undergraduate Teaching in 2016-2017

AST 101 (UTM) - Solar System Astronomy
AST 110 (UTM) - Introduction to Astronomical Observations

Graduate Teaching in 2016-2017

AST 1410 - Stars

Research Interests

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:

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 observable

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.

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.

John Lester

Undergraduate Teaching in 2016-2017

Graduate Teaching in 2016-2017

Research Interests

Current Research Opportunities

Selected Publications

Former Students

Model Atmosphere Programs