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Spring 2009

Jan 9
 Prof. Jean-Luc Margot (UCLA)
Solar System Binaries
I will summarize results from recent observational and theoretical studies of binary systems in near-Earth asteroids (NEAs), main belt asteroids (MBAs), and trans-Neptunian objects (TNOs). We seek to characterize the physical properties, formation mechanisms, and evolutionary processes of the binaries with the goal of placing data constraints on the formation and evolution of small bodies in the solar system.
Host: Yanqin Wu
Jan 16
 Prof. Luigi Gallo (Saint Mary)
Narrow-line Seyfert 1 galaixes: revealing the innermost regions of active galaxies
X-ray observations of narrow-line Seyfert 1 (NLS1) galaxies depict some of the most extreme conditions seen in active galactic nuclei (AGN). The complex X-ray spectra and outstanding variability reveal information about the regions closest to the supermassive black hole (within a few gravitational radii). I will present some of the most sensitive X-ray observations of NLS1s and describe how they can be understood in terms of ionised reflection. I will also present observations of NLS1s at other wavebands demonstrating how they fit into the general AGN picture.
Host: Dae-Sik Moon
Jan 23
 Prof. Ue-Li Pen (CITA)
21cm cosmology
Recently it has been realized that a new approach may allow rapid mapping of substantial fractions of the Hubble volume in 21cm. The "Intensity Mapping" technique is a new window on the universe, which instead of detecting individual galaxies, directly maps large scale structure using a compact radio telescope. This generalizes earlier pictures, which includes the epoch of reionization, making the whole visible Hubble volume accessible to existing low frequency radio telescopes, and enabling unprecedented precision cosmology with proposed dedicated surveys. We report on the initial results and future potential.
Host: Yanqin Wu
Jan 30
 Dr. Laura Ferrarese (HIA)
The Structure of Early-Type Galaxies from the ACS Virgo and Fornax Cluster Surveys
A total of 143 early-type members of the Virgo and Fornax clusters have been observed with the Advanced Camera for Surveys on board the Hubble Space Telescope as part of the ACS Virgo and Fornax Cluster Surveys. The surveys and their extensions consist of ACS/WFC multicolor imaging, supplemented by spectroscopy and/or additional imaging from WFPC2, NICMOS, Chandra, Spitzer, Gemini, Keck, KPNO, CTIO and CFHT. In this talk I shall review findings from the surveys that are relevant to the formation and evolution of galactic spheroids across the Hubble sequence and galactic luminosity function, including the properties of globular cluster systems, central and global surface brightness profiles, and central massive objects. In the last part of the talk I will briefly present the natural successor to the ACS Virgo Cluster Survey: the Next Generation Virgo Cluster Survey (NGVS), a large CFHT program that will survey the Virgo cluster, from its core to virial radius, to unprecedented depths, in five filters. A description of the NGVS can be found on the project website: http://www.astrosci.ca/NGVS/
Host: Dae-Sik Moon
Feb 9
MP102		 Prof. Peter Michelson (Stanford)
A New View of the High-Energy Universe: Results from the first 6 months of the Fermi Gamma-ray Space Telescope
Gamma-ray Space Telescope (formerly GLAST) was launched by NASA on June 11, 2008. The Large Area Telescope (LAT) instrument measures cosmic gamma-ray radiation in the energy range 20 MeV to >300 GeV, with measurements by the GLAST Burst Monitor (GBM) of gamma-ray bursts from 8 keV to 30 MeV. The LAT, with a large improvement in sensitivity, large field-of-view, and much finer angular resolution compared to previous high-energy telescopes, observes 20% of the sky at any instant and covers the entire sky every 3 hours. Fermi is providing an important window on a wide variety of high-energy phenomena, including pulsars, black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for new phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang.  I will describe the Fermi observatory and provide an overview of the observations made to date.
Host: Dick Bond
Feb 13
 Dr. Marcus Janson (Toronto)
High-conrtast imaging searches for planets around Eps Eri and Eps Ind
At distances of only 3.3 and 3.6 pc respectively, Eps Eri and Eps Ind are two of the most nearby solar-type stars. In addition, they both exhibit linear radial velocity trends indicative of planetary companions at relatively large separations, making them potentially interesting for the purpose of direct imaging. In this talk, I discuss the results of deep imaging campaigns of the two stars, using high-contrast imaging at 4 micron, which has been demonstrated to be an ideal technique for bright and relatively old stars with the presently available instrumentation. The combination of dynamical and imaging data places strong constraints on the system parameters, to the extent that any planets more massive than 3 Mjup can be excluded everywhere in the Eps Eri system, and that a consistent picture of the Eps Ind system can only be attained if it is substantially older than the most commonly quoted age estimates of around 1 Gyr.
Host: Ray Jayawardhana
Feb 20 (Reading week)
Feb 27
 Dr. Elena D'Onghia (CfA)
The origin of dwarf spheroidal galaxies
The most dark matter dominated galaxies known are the dwarf spheroidals, but their origin is still uncertain. The recent discovery of ultra-faint dwarf spheroidals around the Milky Way further challenges our understanding of how low-luminosity galaxies originate and evolve because of their even more extreme paucity of gas and stars relative to their dark matter content. By employing numerical simulations we propose that interactions between dwarf disc galaxies can excite a new gravitational process that immediately drives their evolution into spheroidals in groups of dwarfs before they are accreted into large systems like the Milky Way. This effect, which is purely gravitational in nature, is distinct from other mechanisms which have been proposed up to now to explain the origin of dwarf spheroidals, such as merging, galaxy-galaxy harassment and more general heating processes, or tidal and ram pressure stripping. This new process can account for the observed properties of the dwarf galaxies including their morphologies, kinematics, and extreme high ratios of dark to luminous matter. Under some circumstances it can lead to even more efficient stripping of the baryons, yielding objects that resemble the ultra-faint dwarfs and ultimately systems that are nearly completely dark.
Host: Ray Carlberg
Mar 6
 Prof. Scott Hughes (MIT)
Exploiting the two-body problem in general relativity
A simple problem in Newtonian gravity, the motion of two bodies about one another is far more challenging in general relativity. Motivated largely by the anticipated importance of compact binaries as gravitational-wave sources, many years of effort have produced a suite of tools for modeling binaries in general relativity. This work has culminated in the celebrated recent breakthroughs in numerical relativity allowing us to model essentially arbitrary compact binary systems. In this talk, I will present an overview of what we have learned from GR's two-body problem, focusing in particular on how unique aspects of general relativity flavor the gravitational waves which binaries generate. I will also describe how measuring these waves and exploiting these models will allow us to study compact bodies, especially black holes, in exquisite detail.
Host: Samaya Nissanke
Mar 13
 Prof. Alice Shapley (UCLA)
The Metallicities and Physical Conditions in Star-forming Galaxies at High-Redshift
The abundance of heavy elements in the ISM of star-forming galaxies represents a fundamental metric of the galaxy formation process. This metallicity reflects the gas reprocessed by stars, and the metals returned to the ISM by supernova explosions. Furthermore, galaxies display universal correlations among luminosity, stellar mass, and metallicity. The form and evolution of these correlations as a function of redshift lend insight into the infall and outflow of gas in galaxies as they build up their stellar populations, and provide important constraints on the nature of star-formation "feedback," a crucial ingredient in models of galaxy formation. Here we present evidence, based on rest-frame optical spectroscopy of galaxies at z~1.0-2.5, that the physical conditions in star-forming regions at high redshift are qualitatively different from those in the local universe. In particular, we present brand-new and unusually high S/N spectra probing the star-forming regions of strongly-lensed z~2 star-forming galaxies. The observed empirical differences in the spectra of distant galaxies have implications for understanding galaxy metallicities and, perhaps more fundamentally, star formation, itself, during an important epoch when the properties of today's galaxy population were still in the process of coming into place.
Host: Dae-Sik Moon
Mar 20
 Prof. Luis Ho (Carnegie)
The Coevolution of Black Holes and Galaxies: Recent Developments
I will review observational progress in defining and refining the various empirical scaling relations between black hole masses and host galaxy properties. I will emphasize ways in which the intrinsic scatter can be quantified, and whether the scatter correlates with physical properties. I will discuss how to extend the scaling relations to active galaxies, and summarize preliminary efforts to probe the evolution of these scaling relations. I will present new measuremnts of th cold ISM content in AGN host galaxies, and constraints they place on current models of AGN feedback. Lastly, I will discuss a new class of low-mass black holes in bulgeless and dwarf galaxies that serve as local analogs of seed supermassive black holes.
Host: Howard Yee
Mar 27
 Prof. Roger Chevalier (Virginia)
Pulsar nebulae and their high energy emission
The relativistic wind from a newly formed pulsar creates a bubble of magnetic field and relativistic particles in the surrounding supernova gas. The evolution of the pulsar nebula depends on the properties of the supernova and its interaction with the interstellar medium. Recent observations at very high (TeV) gamma-ray energies have shown that pulsar nebulae constitute the dominant high energy population in our Galaxy. The implications of these observations for the nature of pulsar nebulae will be discussed.
Host: Marten van Kerkwijk & Dae-Sik Moon
Apr 3 Dr Andrew West (MIT)
Galactic Stratigraphy, Magnetic Activity and the Kinematics of M dwarfs: Probing the Evolution and Structure of the Milky Way with it's Smallest Constituents
M dwarfs are the smallest stars in the Galaxy that can still fuse hydrogen. They can be 10 times less massive, twice as cool and over 1000 times dimmer than the Sun. Yet despite their diminutive physical properties, M dwarfs make up ~75% of all of the stars in the Milky Way and have main sequence lifetimes that exceed trillions of years . Their dominance in the Galaxy make M dwarfs excellent tracers of both the structure and evolution of the local Milky Way. In addition, these little stars have intense stellar flares and strong magnetic fields that allow us to probe their interiors and may have important consequences for the habitability of planets that orbit them. Current astronomical surveys have allowed astronomers to construct samples that contain millions of M dwarfs - more than those for any other type of star.
Apr 28
Tue, 3PM!		 Prof. James Graham (Berkeley)
Direct Detection of Exoplanets: The Gemini Planet Imager & Fomalhaut b
I will discuss current and future work related to the direction detection of extrasolar planets, including: 1) a program using the Advanced Camera for Surveys on the Hubble Telescope and; 2) the Gemini Planet Imager (GPI). 1) The 100 Myr-old A star Fomalhaut hosts a belt of dusty material with a morphology that implies the presence of a shepherding planet. The Hubble Space Telescope has detected a common proper motion companion, Fomalhaut b, with properties consistent with the predicted exoplanet. Two epochs of optical data reveal Keplerian orbital motion. The mass of Fomalhaut b is less than three Jupiter masses: a more massive object would disrupt the dust belt and would have been detected in deep H and L' images obtained with the Keck and Gemini Observatories. 2) The Gemini Planet imager is an "extreme" adaptive optics system being designed and built for the Gemini Observatory. GPI combines precise and accurate wavefront control, diffraction suppression, and a speckle-suppressing science camera with integral field and polarimetry capabilities. GPI's primary science goal is the direct detection and characterization of young, Jovian-mass exoplanets. For systems younger than 2 Gyr exoplanets more massive than 6 Jupiter masses and semimajor axes beyond 10 AU are detected with completeness greater than 50%. GPI will also discover faint debris disks, explore icy moons and minor planets in the solar system, reveal high dynamic range main-sequence binaries, and study mass loss from evolved stars.
Host: Dunlap Institute
May 14
Thu, 3PM!		 Prof. Steve Eikenberry (U. Florida)
Exploring Black Hole Astrophysics in the Infrared
I will review the relatively young field of black hole studies using multi- wavelength (particularly infrared) observational techniques. I will focus on the insights this is providing into the physics of ``microquasars'' — stellar-mass black hole binaries exhibiting relativistic jet outflows — and the mass evolution history of supermassive black holes. I will also place special emphasis on new instrumentation we are developing to advance this field, including the upcoming FLAMINGOS-2 Galactic Center Survey.
Host: Dunlap Institute
Last modified: 01 May 2009, 12:55:06

Yanqin Wu (wu@astro) /Dae-Sik Moon (moon@astro) / Ray Jayawardhana (rayjay@astro) / Marten van Kerkwijk (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