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First half of 2005

Jan 14 Dr Jarle Brinchmann (Univ. do Porto)
Physics hidden in galaxy spectra and the physical properties of low-z galaxies
A galaxy's spectrum contains a wealth of physical information, and the steadily increasing number of galaxy spectra with high resolution has provided a strong incentive to develop methods to extract as much physical information from galaxy spectra as possible. In this talk I will summarise some recent work we have been carrying out to extract physical properties of galaxies from their absorption and emission features and discuss briefly when these methods are useful for other projects. I will present an inventory of star formation and stellar metallicity in the local universe using spectra of >200k SDSS galaxies and how they depend on the physical properties of the galaxies.
Host: Bob Abraham
Jan 17
Mo.3PM
MP 203		 Prof. Ewine van Dishoeck (Leiden Obs.)
Gas and ice in protoplanetary disks
In the last decade, it has been well established that many pre-main sequence stars are surrounded by disks with sizes and masses comparable to those of our own primitive solar system. While much attention has been paid to the analysis of continuum data, line observations can provide important complementary information on the physical structure and chemical composition of disks. High-J lines of CO and other simple gas-phase molecules (including deuterated species) have been obtained with the JCMT and OVRO to constrain the temperatures and densities, as well as the chemical abundances. The presence of abundant ices in the cold part of disks is suggested by recent data from VLT-ISAAC and the Spitzer Space Telescope. The results will be discussed in the context of models of flared and non-flared disks and their evolution from protostellar regions. The importance of new observational facilities, in particular ALMA, JWST and Herschel, will be emphasized.
Host: CITA and Helen Sawyer Hogg Visitorship
Jan 18
Tu.3PM
LM 162!		 Prof. Ewine van Dishoeck (Leiden Obs.)
The physical and chemical structure low-mass protostellar envelopes: from JCMT to Herschel and ALMA
Host: Helen Sawyer Hogg Visitorship
Jan 19
We.3PM
MP 137		 Dr Dae-Sik Moon (Caltech)
Experimental Efforts to Study Core-collapse Supernovae and associated objects in the Infrared and Optical
Core-collapse supernovae (SNe) produce diverse interesting objects such as Type Ibc/II SNe, neutron stars and X-ray binaries, supernova remnants and pulsar wind nebulae, and at least some fraction of gamma-ray bursts. I will present several experimental and instrumentation projects underway at Caltech to study these objects in the infrared and optical. These include building a new near-infrared spectrograph for the Keck telescope, roboticization of the Palomar 1.5-m telescope, and development of a new infrared detector technology. I will emphasize the synergy with observations in the high-energy wavebands.
Host: Marten van Kerkwijk
Jan 24
Mo.3PM
MP 408		 Dr David Sand (Caltech)
The dark matter density profile in galaxy clusters
One of the basic predictions of the cold dark matter paradigm is that dark matter halos ranging in size from dwarf galaxies to galaxy clusters have a cuspy density profile. Along with a brief review of recent measurements of the dark matter density profile at the galaxy cluster scale, I will present observational results from two programs which have sought to disentangle luminous from dark matter in galaxy cluster cores in order to probe the dark matter profile directly. I will also discuss near-future prospects for combining multiple observational techniques in order to get a complete empirical picture of the typical total cluster mass distribution.
Host: CITA
Jan 28 No colloquium: Speaker cancelled
Feb 4 Dr Aleks Scholz (UofT)
Rotation and variability of very low mass objects
The regulation of angular momentum is one of the key processes for our understanding of stellar evolution. The rotational evolution of a solar-mass star is mainly determined by the magnetic interaction with the circumstellar disk and angular momentum loss through stellar winds, and depends thus critically on the properties of the magnetic field of the star. For solar-mass stars, hundreds of rotation periods have been measured, which set strong constraints for models of rotational evolution. However, we are lacking a comparable database for very low mass objects, i.e. brown dwarfs and stars with masses below 0.4 solar masses. In contrast to more massive stars, these very low-mass objects are believed to be fully convective. This may lead to major differences in terms of rotation and activity, since fully convective objects cannot host a solar-type dynamo. In this talk, I will report on our observational efforts to understand the rotational evolution of very low-mass objects.
Feb 9
We.3PM
MP 137		 Dr Mike Gladders (Carnegie)
Understanding high-redshift galaxy clusters as cosmological probes: Recent results and instrumentation developments
A number of large survey programs aim to use clusters as a fundamental cosmological probe. However, realisation of these grand plans requires major steps forward in our understanding of galaxy clusters over cosmic time. I will discuss recent results from one of the largest existing optical cluster surveys - the Red-Sequence Cluster Survey (RCS). Extensive follow-up programs show that the most distant clusters are rather different from local counterparts. Motivated by these differences, I will highlight the ongoing development of two new instruments for the Magellan telescopes which are aimed at providing new capabilities for studying high-redshift galaxy clusters in detail. The first instrument, LDSS-3, is an ultra-high-throughput multi-object spectrograph for the Clay telescope. The second, GISMO, is a unique image reformatter which works in concert with the 1/2 degree field IMACS spectrograph to provide highly multiplexed spectroscopy over a small (3'.75x3'.25) field of view with an areal density of slits up to 8x that allowed in a typical MOS.
Host: Howard Yee
Feb 11 Dr David Kaplan (MIT)
Searching for compact objects in supernova remnants
We have undertaken a census of the central sources in supernova remnants within 5 kpc. For remnants that have no evidence for central sources (i.e. shell-type remnants), we have searched for new sources with the Chandra X-ray Obervatory. We will describe the execution and major results from our census.
Host: Marten van Kerkwijk
Feb 16
We.3PM
MP 137		 Dr Anand Sivaramakrishnan (STScI)
In Search of Other Worlds: Extreme Adaptive Optics Coronagraphy
Planetary and disk science is about to advance into uncharted scientific territory with the installation of the near-IR Lyot Project coronagraph on a working 1000 actuator adaptive optics system on the 3.6 m AEOS telescope in Hawaii. Even more ambitious adaptive optics systems, possessing a few thousand corrective channels, are being designed for 8 m class ESO VLT and Gemini telescopes, with first light planned in five years. I will present some of the the scientific capabilities of this new generation of Extreme Adaptive Optics (ExAO) coronagraphs, and highlight areas of coronagraphy which need to be understood and developed in order to attain the scientific results such systems are intended to achieve.
Host: Peter Martin
Feb 18 Dr Colin Borys (Caltech)
Understanding the high redshift SCUBA galaxies: New observations from Spitzer, HST, and SHARC-II
The difficulties in discerning the nature of the cosmologically significant population of dusty galaxies observed by SCUBA and MAMBO, their redshift distribution, and how they relate to optically selected high redshift galaxies are now being largely overcome by using an armada of new instruments. This talk will present a diverse set of observations towards sub-millimeter detected galaxies from a host of new ground and space-borne facilities. Starting at low redshift, I will show how SHARC-II 350 micron observations of IRAS galaxies can weigh in on the debate surrounding sub-mm photometric redshift estimators. Using a silicate absorption feature in the mid-IR, I will demonstrate a new technique that can be used to select large samples star-forming galaxies at intermediate redshifts (z~1.5) via Spitzer imaging. Finally high resolution ACS and NICMOS images of high redshift sub-mm galaxies will be presented, showing just how distinct these systems are from UV selected galaxies at similar redshifts.
Host: Ernie Seaquist
Feb 25 Dr Jodi Asbell-Clarke (Technology Education Research Center)
Reaching the `Non-Scientist' through Astronomy
Astronomy is one of the most widely (if not accurately) represented sciences in popular culture which provides an avenue to engage students who may consider themselves non-science oriented. This talk will address two ongoing projects that pursue this goal. The first is a high school astronomy course, Investigating Astronomy, which is under development at TERC to address the needs of Latino students. Investigating Astronomy includes research-based pedagogical strategies that are successful with high-risk, traditionally low achieving students as well as English Language Learners. The second project is an online Life in the Universe course taught for non-science majors at Saint Mary's University. This course uses strategies for engaging online students in a discussion-based community to delve deeply in inquiry about scientific content and to take responsibility for their own learning.
Host: John Percy
Mar 4 No colloquium: G2000 postponed from Feb 9 instead
Mar 11 Prof. Cathie Clarke (IoA)
The dispersal of discs around young stars
This talk will summarise the recent advances in our understanding of how discs around young stars are dispersed. On an observational front, a number of facts are reasonably well established, such as the overall lifetime of protostellar discs (1 to 10 Myr) and the large spread in lifetimes from star to star in a given environment. The most critical observational constraint (which is hard to explain in most theoretical models) is the fact that disc dispersal is governed by two timescales - an overall disc lifetime and a second, much shorter, timescale on which young stars make the transition between disc possessing and discless status. Currently, this latter constraint is met by only two classes of model, in which the inner disc is emptied either by a mixture of photoevaporation and viscous evolution or where it is planet formation that depletes the dust and (possibly) gas content of the inner disc. In this talk, we explore the consequences of disc photevaporation models for the observed properties of disc systems in some detail.
Host: Ray Jayawardhana
Mar 18 Dr Jason Aufdenberg (NOAO)
Testing stellar atmosphere models with high-precision interferometric limb-darkening observations
Limb-darkening observations help to constrain the full radiation field (the intensities) predicted by model stellar atmospheres. Such observations complement traditional spectroscopic tests of model spectra (the fluxes). With the exceptions of A-type stars Sirius and Altair, direct interferometric limb-darkening observations have been limited to a small number of stars cooler than the Sun. I will describe an observational program in which we have obtained limb-darkening measurements B- and A-type supergiants and F-type subgiants. I will also discuss how these limb-darkening measurements are compared to model visibility predictions to provide a mass-loss rate diagnostic for supergiant stellar winds. In addition, I will show how multi-wavelength interferometric observations of Procyon provide detailed tests of 1-D and 3-D convection models.
Host: John Lester
Mar 23
We.12PM
MP1318A		 Dr Gwendolyn Meeus (AIP)
Disc and dust evolution around young, < 10 Myr stars
During the last 10 years, our knowledge about circumstellar discs and dust has increased dramatically. In this talk, I will focus on what we know about the discs of young stars through infrared observations, mainly spectroscopy. After a short introduction, I will focus on Herbig Ae/Be stars. I will discuss current disc models to explain their spectral energy distributions. Infrared spectra will be interpreted in terms of dust properties, which in turn will be linked to the disc models proposed. With the same approach I will give an overview of the discs of the less massive T Tauri stars. To conclude, we will have a glance at brown dwarf disc properties, so that the whole range from substellar to a few solar masses will have been covered. As a last part, I will indicate future directions in which to continue this work.
Host: Alexis Brandeker (joint with SDG)
Mar 25 No colloquium: Good Friday
Apr 1 Dr Roelof de Jong (STScI)
Dark and Luminous Matter in Nearby Galaxies
We have made remarkable progress in recent years in our understanding of galaxy formation and evolution. Deep, high redshift observations have constrained the star formation history of the Universe and have unveiled the evolution of galaxy morphologies. These observations have helped to build and solidify our current model of hierarchical structure and galaxy formation, in the favored Lambda Cold Dark Matter (CDM) paradigm. However, while very successful on scales of galaxies and larger, CDM faces a number of problems on smaller scales where "gastrophysics" comes into play. These problems relate to central density distribution of the dark matter halos, the angular momentum distribution of galaxy disks, and the lack of (stellar) substructure in galaxy sized halos. In my talk I will present observational constraints on the dark matter and angular momentum distribution problems, using a new technique to determine the stellar masses in disk galaxies. I will furthermore present new programs I have started to address the substructure problem by investigating stellar halos and tidal streamers.
Apr 8 Dr Marie Treyer (Caltech)
Ultraviolet galaxies from z=0 to ~1: first results from the GALEX mission.
I will present the Galaxy Evolution Explorer (GALEX) mission and some of its first results, focusing on the statistical properties of UV selected galaxies and their evolution with redshift. GALEX consists of a series of nested imaging and spectroscopic surveys in 2 bands (1500A and 2300A). The UV data matched to various large spectroscopic surveys (e.g. SDSS, 2dF, VVDS) and multi-wavelength imaging surveys provide unprecedented samples of star forming galaxies from the local Universe to z>1. The most recent GALEX data release (GR1) is available from the Multimission Archive at Space Telescope (MAST).
Host: Mark Sullivan
Apr 15 Prof. Thomas Henning (MPIA, Heidelberg)
Grain Growth in Protoplanatery Disks - From dust to pebbles
Planet formation starts with the growth of grains in protoplanetary disks. This talk will review the observational evidence for grain growth in such disks, with special emphasis on mid-infrared spectroscopy and millimetre interferometry. This discussion will also include the first results from VLTI mid-infrared interferometry. The talk will cover the main physical processes, which lead to grain growth and will highlight the present problems in our understanding of planetesimal formation. Furthermore, the change of disk structure caused by grain growth and subsequent sedimentation towards the disk midplane will be discussed.
Host: Ray Jayawardhana
Apr 22 Prof. Jon Willis (UVic)
ZEN and the search for high-redshift galaxies
The study of the most distant objects in the Universe places unique constraints upon the nature of the early Cosmos. Over the past 80 years the known Universe has expanded dramatically with advances in telescope and detector technology, and has been accompanied by a growing insight into the formation of the first galaxies and quasars.
Current observations of the most distant galaxies and quasars extend to when the Universe was only 13% of its current size (a redshift z = 6.6 - equivalent to a look-back time of 12.6 Billion years) and place unique constraints upon the formation and distribution of the first stars together with the physical state of the high-redshift inter-galactic medium. I will present the initial results of an ambitious observational programme which aims to extend studies of distant galaxies to a redshift z = 9 (Z Equals Nine - ZEN). The program employs some of the deepest astronomical images currently in existence and places important constraints upon high-redshift star-formation and the role of neutral gas in the early Universe.
Host: Howard Yee
Apr 29 Prof. Zoltán Haiman (Columbia)
How Did the Cosmic Dark Age End?
In the currently favored cosmological paradigm, the first non-linear objects are small dark matter halos that formed at redshift z~30. The pristine primordial gas in these halos can dissipate its energy by excitations of molecular hydrogen, and contract to high densities to form the first generation of stars and black holes. These objects subsequently evolve into the population of well-studied galaxies and quasars at redshift z<6. The first stars and black holes, however, can have a significant impact on the rest of the universe as soon as they appear, by photo-ionizing most of the baryons. The cosmic microwave background anisotropies (measured by the Wilkinson Microwave Anisotropy Probe), and the spectra of the most distant quasars (discovered in the Sloan Digital Sky Survey), have recently provided the first glimpses of the early ionization history of the universe. I will discuss several alternative interpretations of these recent observations. In the next decade, new instruments should characterize the ionization history and tomography in detail, and allow us to infer the abundance, spectrum, and other properties of the first generation of astrophysical objects.
Host: Ray Jayawardhana
Last modified: 19 Dec 2005, 12:29:32
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