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Second half of 2004

Sep 17 Dr Alexis Brandeker (UofT)
Riddles of the beta Pictoris gas disk
In the last two decades, increasingly sensitive observations have been able to detect emission from dusty disks around stars of widely different ages. As a result, we now have some information on the general evolution of the dust in disks. The evolution of the gas in disks, however, has been much more difficult to assess, mostly due to the difficulties in detecting the cold disk gas of older disks. I present results from recent searches for disk gas. In particular, I discuss spatially resolved observations of gas around the main-sequence star beta Pictoris, where we find emission from metallic gas as far out as 323 AU from the star and 77 AU above the disk mid-plane. Considerations of the strong radiation pressure on the metallic gas suggest the presence of an invisble braking force. The assumption of this force being gas friction against hydrogen leads to hydrogen gas densities inconsistent with previous observations. Other, slightly more exotic possibilities are discussed.
Sep 24 Dr Bruce Macintosh (LLNL)
Direct detection of extrasolar planets with current and future adaptive optics
More than 100 extrasolar planets have so far been detected through indirect techniques - all in <5 AU orbits. Direct imaging detection of extrasolar planets will be one of the most significant next steps, allowing characterization of temperature and composition. I will discuss an ongoing search for very young (<100 Myr) planets in >20AU orbits using adaptive optics (AO) on the Keck telescope. To truly probe solar-system-like scales (5-20 AU) will require next-generation "Extreme" adaptive optics systems; I will summarize our scientific rationale and design for such a system for the Keck or Gemini telescopes.
Host: Ray Carlberg
Oct 1 Dr Marcin Sawicki (DAO)
The differential evolution of the star-forming galaxy population from z~4 to z~2
I will present results from an extremely deep ground-based imaging survey on Keck, reaching galaxies with star formation rates of only ~1 solar mass per year, and yielding the first robust measurement of the galaxy luminosity function at z~2 and of the faint end of the luminosity function at z~3 and 4. These data show that as the Universe doubles its age from z~4 to z~2 the faint end of the luminosity function is evolving with lookback time, while the bright end remains virtually unchanged. Because this evolution is differential with luminosity, it points to new avenues for studying how galaxies form in the early Universe.
Host: Howard Yee
Oct 8 Dr Russel White (Caltech)
Unveiling the Protostar Imposters in Taurus
We present high dispersion optical spectra of 36 stars in Taurus-Auriga whose circumstellar environment suggests that they are younger than T Tauri stars. Many of the stars are seen only via scattered light and the majority have never been spectroscopically observed previously. These spectra, in combination with longer wavelength measurements, are used to reassess the evolutionary state of protostars relative to optically revealed T Tauri stars. We draw the somewhat controversial conclusion that most so-called protostars have already acquired the majority of their mass and are much older than traditionally assumed.
Host: Andy Howell
Oct 15 Dr Andy Howell (UofT)
Type Ia Supernovae and the SN Legacy Survey
I will review recent developments in the field of Type Ia Supernovae (SNe Ia), including the first year of observations from the SN Legacy Survey (SNLS). SNe Ia make excellent standard candles -- they were used to measure the acceleration of the universe and discover the Dark Energy driving this acceleration. Now with the SNLS we hope to measure "w" -- the equation of state of the Dark Energy -- by discovering and following about 700 Type Ia supernovae over 5 years. Meanwhile, progress is being made on unraveling the mystery of the progenitor systems of SNe Ia, which should improve their use as standard candles. Population studies, lightcurves, spectroscopy, and spectropolarimetry are starting to yield concrete, though somewhat puzzling, clues about the progenitor systems and explosion model behind the most consistent explosions in the universe.
Oct 22 Dr Julia Lee (CfA)
Probing Black Hole Environments with High Resolution X-ray Spectroscopy
Black holes and accretion onto black holes are associated with a wide range of astrophysical phenomena. High resolution X-ray spectroscopy provides a powerful new tool for probing the physics of the black hole environment. X-ray spectral signatures reveal the dynamics and the ionization state of plasma in and around the accretion disk, and the properties of winds and flows. I will discuss highlights from Chandra observations of several well known stellar and supermassive black hole systems, GRS 1915+105, MCG-6-30-15 and IRAS 18325-5926 to illustrate their similarities, despite the phenomenological differences.
Host: Marten van Kerkwijk
Oct 29 Prof. Ian Short (Saint Mary's)
Stellar atmospheric models and the problem of chemical composition
Stars are among the primary tracers of the chemical composition of the galaxy as a function of position and time. Therefore, our knowledge of structure formation and evolution, the nature of first generation stars, and the origin of all the chemical elements heavier than Helium all depend on accurate measurement of stellar chemical abundances. The accuracy of spectroscopically inferred abundances depends on the physical realism with which stellar atmospheric structure and spectrum formation are modelled. Even for the Sun, knowledge of the abundance of some astrophysically important elements is significantly uncertain due to unrealistic modelling. I report on recent advances on one particular aspect of realism: the modelling of the thermodynamic state of the gas and radiation field in a star's atmosphere. I focus on the Sun as a test case.
Host: Tom Bolton
Nov 5 Dr Doug Johnstone (HIA)
An extinction threshold for star formation in Ophiuchus: A taste of the SCUBA2 future.
The problem of star formation is not forming stars, but rather not forming stars. Indeed, gravitational collapse would proceed quickly in most molecular clouds if not for the addition of non-thermal support mechanisms such as turbulent motions and magnetic fields. Only recently have observations of molecular clouds become sufficient to rigorously test the various theoretical models for cloud support. In this talk I will discuss an ongoing survey, the
COMPLETE Survey of Molecular Clouds, and the recent discovery of an extinction threshold for structure formation within Ophiuchus. I will end the talk with a look at the future of molecular cloud observations in the era of SCUBA2 and HARP at the JCMT, and the arrival of ALMA. Will Star Formation studies become much more similar to Cosmological studies?
Host: Norm Murray
Nov 12 Dr Rachel Somerville (STScI)
The Great Observatories Origins Deep Survey: overview and recent highlights
The Great Observatories Origins Deep Survey (GOODS) is a pan-chromatic deep survey, designed to study the evolution of galaxies and AGN over most of cosmic history. GOODS combines deep imaging from space with the Advanced Camera for Surveys (ACS) on HST, the Chandra X-ray Observatory, and the Spitzer Space Telescope, with ground based imaging and spectra from the optical to the radio. I will discuss several recent science highlights from the first year of the survey, including constraints on dark energy from high redshift supernovae, the evolution of the cosmic star formation history back to z~6, the evolution of galaxy sizes, and the nature of 'exotic' populations like Extremely Red Objects (EROs) and EXOs (extreme X-ray/Optical flux ratio objects). I will conclude by discussing the promise of the ongoing observations with the Spitzer Space Telescope.
Host: Ray Jayawardhana
Nov 19 Dr Ben Lane (MIT)
A high-precision astrometric planet search
I will discuss recent developments in ground-based astrometry. Using a long-baseline optical interferometer it is possible to measure the relative positions of two closely (about 1 arcsecond) separated stars, so-called speckle binaries, to a precision of 20 micro-arcseconds or better. This level of precision can be used for a variety of exciting purposes, including finding Jupiter- and Saturn-mass planets. It can also potentially be used to derive stellar masses with precisions of an entirely new order: 0.01%.
Host: Marten van Kerkwijk
Nov 26 Prof. Michael Balogh (Waterloo)
How to kill a galaxy: stripping, harassment, strangulation and more
The evolution of galaxies is governed both by local processes, and by interactions with the surrounding environment. In this talk I review (primarily) observational progress in our understanding of how hostile environments terminate star formation in galaxies. Specifically, the SDSS and 2dFGRS surveys allow a detailed analysis of the correlations between galaxy properties and their environment at the present day. We can use these surveys as a baseline to trace evolution in both rich clusters and, more recently, galaxy groups. These new results show that group environments are likely responsible for rapid transformations between gas-rich, star forming galaxies and the elliptical, passively-evolving population that dominates today's clusters.
Host: Howard Yee
Dec 2
with Physics
Th. 4PM!
Dr Scott Ransom (NRAO)
The Incredible Double-Pulsar Binary J0737-3039: A pulsar ``Holy Grail'' at last
Earlier this year, an international collaboration anounced what is arguably the most important pulsar system yet discovered -- a nearby (about 600 pc), compact (orbital period 2.4 hrs), highly relativistic, and eclipsing double-pulsar binary. This system displays an amazing variety of rare and/or unique phenomena and promises to revolutionize our understanding of many areas of pulsar physics. In this talk I will briefly describe the genesis of the system, its current behaviour, and predictions for its future. Much of this information comes from Green Bank Telescope observations of the pulsars that constrain eclipse and flux variability mechanisms, the orbital and spin geometries, as well as the magnitude and direction of the ``kick'' imparted by the second supernova.
Host: Marten van Kerkwijk
Dec 3
Extra!
Dr Scott Ransom (NRAO)
Hittin' the Pulsar Jackpot in Terzan 5 with the GBT
Terzan 5 is a dense globular cluster near the Galactic center that has been predicted for more than 15 years to contain tens or even hundreds of millisecond pulsars. But deep searches with the Parkes and Lovell telescopes had only managed to uncover 3 pulsars over the same period of time. This summer and fall, several observations at 2GHz with the Green Bank Telescope significantly changed all that with the discovery of (at least) 20 new millisecond pulsars, most of which are in binary systems. Several of these binaries are truly unique and/or exotic systems, and two them provide strong evidence for the existence of "massive" neutron stars (>1.6 Msun). In this talk I'll discuss the reasons behind the project, the observation itself, and some of the implications of the new discoveries.
Host: Marten van Kerkwijk
Dec 10
MP 134!
Prof. Tim Heckman (JHU)
Spectroscopy of 200 Kilo-Galaxies: Implications for Cosmic Gastro-Physics
We now have a very successful and tightly constrained model for the cosmic evolution of the structure of dark matter. The challenge is now to understand the ``gastrophysics'' by which the luminous baryons in the universe are painted onto the dominant dark matter component. This requires understanding the gas/star/black-hole ecosystem. The on-going Sloan Digital Sky Survey (SDSS) affords us the opportunity to examine the fossil record of galaxy and black hole evolution with unparalleled precision. I will summarize recent work based on optical spectra of over 200,000 SDSS galaxies, and the methodology we have developed to measure the basic properties of these galaxies and of the active nuclei (accreting black holes) present in many of them.
Host: Norm Murray

Last modified: 12 Dec 2004, 11:14:32
Marten van Kerkwijk / MP 1404D / 416-946-7288 / mhvk@astro
Colloquia are Fridays, at 2 PM, in Cody Hall. They are followed by refreshments in the lounge, AB 201.

Instructions for speakers

Schedule with abstracts

Schedule without abstracts

Student seminars

CITA seminars

Physics colloquia

Past colloquia: 2003A, 2003B, 2004A, 2004B, 2005A, 2005B, 2006A, 2006B, 2007A, 2007B, 2008A, 2008B, 2009A, 2009B, 2010A, 2010B, 2011A

Current colloquia: 2011B