University of Toronto Astronomy Colloquia



	ASTRONOMY COLLOQUIA

Spring 2011

Jan 21	Dr. Mike Jura (UCLA) *The Composition of Extrasolar Asteroids* Polluted white dwarfs are a uniquely powerful tool to study the elemental composition of extrasolar minor planets. In the tiny sample measured to-date, as with the bulk Earth, it appears that four elements -- oxygen, magnesium, silicon and iron are dominant. We are now investigating several topics. Are there extrasolar carbon planets? Do extrasolar planets differentiate and form iron cores? Is water widespread within extrasolar planets?
Jan 24 Mon, 3PM MP 202	Dr. Nicholas Law (Dunlap Institute for Astronomy & Astrophysics,U of T) *Small Stars, Giant Planets, and a Really Big Survey: The PTF Search for Planets Around M-dwarfs* PTF/M-dwarfs is the largest search for transiting planets around cool stars, covering over 100,000 M-dwarfs. The survey is a Key Project of the Palomar Transient Factory (PTF), a fully-automated, wide-field survey aimed at a systematic exploration of the optical transient sky. I will describe the PTF instrumentation and survey design before presenting the first cool star companions discovered by PTF/M-dwarfs. Finally, I will discuss possibilities for future transit surveys conducted from the Canadian Arctic.
Jan 28	Marc-Antoine Miville-Deschenes (IAP, Paris) *Planck Early Results : a (biased) guided tour* Earlier this month 25 papers were released, presenting the first Planck results. These results do not address the cosmology yet but they cover a wide range of topics, from Galaxy clusters, radio and infrared galaxies to interstellar dust. Anticipating that the foreground (Galactic and extra-galactic) emissions would be the main sources of noise for the Cosmic Microwave Background measurement, the Planck mission was design in order to get the best handle possible on these contaminants. The first results are about them. After introducing the Planck mission itself and its behavior in flight, I will present a subset of the Planck Early Results focusing on the ones on the Galactic interstellar medium and the cosmic infrared background.
Jan 31 Mon, 4PM MP 103	Dr. David Sand (Harvard/UCSB) *Supernovae in galaxy clusters with the Multi-Epoch Nearby Cluster Survey and the future of time domain astrophysics with robotic spectroscopy* I will discuss the Multi-Epoch Nearby Cluster Survey (MENeaCS), a long term program aimed at characterizing the supernova properties in low redshift galaxy clusters. MENeaCS has discovered 23 cluster SN Ia and 7 core collapse SNe in the 58 X-ray selected galaxy clusters (0.05 < z < 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. I will present results on three topics: the intracluster stellar mass fraction in clusters, the environmental dependence of the SN Ia rate, and the usof SN Ia in galaxy clusters to constrain the progenitor of Type ISNe. Finally, taking a step back, I will discuss FLOYDS, a low dispersion robotic spectrograph being built at Las Cumbres Observatory. The main purpose of FLOYDS is to broaden the scope of spectroscopic observations in the time domain beyond what is possible with classically scheduled telescopes -- whether it be rapid follow-up of transients or long-term monitoring campaigns. In the era of large time domain surveys, such as Pan-STARRS and LSST, robotic spectroscopy will play a critical role.
Feb 03 Thu, 3PM MP 202	Dr. Shelley Wright (UCB) *Observing Galaxy Evolution: The Exciting Promise of Adaptive Optics Instrumentation* Studies of galaxies in the early universe (z > 1) have greatly benefited from recent advances in diffraction-limited techniques on 8-10m telescopes using adaptive optics (AO) and integral field spectroscopy. These innovative spectrographs have led to significant scientific achievements and are stimulating the design of future instrumentation. My talk will focus on development and use of the latest near-infrared instruments behind Keck Observatory's AO system. I will present OSIRIS and Keck AO observations of spatially resolved optical emission lines (e.g., Hα, and [N II]) from high-redshift (1 < z < 3) star forming galaxies. These results are part of an ongoing survey to study the dynamics, chemical abundances, and active galactic nuclei (AGN) in early galaxies. The high spatial resolution and 2D capability of an integral field spectrograph has allowed the discovery of some of the lowest luminosity AGN known at this epoch, and I will discuss their potential impact on high-redshift metallicity studies and galaxy formation. Lastly, I will discuss future AO instrumentation on extremely large telescopes (30m), which will offer extraordinary potential to probe the dynamics, assembly, and abundances of galaxies in the early universe.
Feb 04	Dr. David Law (UCLA) *Galactic Archaeology with the Sagittarius Stellar Tidal Stream* Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work has yielded conflicting results: While the angular position of the Sgr leading arm is most consistent with a spherical or slightly oblate Galactic dark matter halo, the radial velocities and distances of stars in this arm are best matched by prolate halo models. I demonstrate that this apparent paradox can be resolved by adopting a fully triaxial halo model, in which it is possible to simultaneously satisfy all major observational constraints on the orbital path of the Sgr stream. In this model, the minor axis of the dark halo is approximately coincident with the Galactic X axis connecting the Sun and the Galactic Center. This collquium is hosted by DI
Feb 07 Mon, 4PM MP 103	Dr. Karin Oberg (Harvard) *Pathways to chemical complexity during star- and planet-formation* Complex organic molecules (>6 atoms) have been detected toward low- and high-mass protostars, galactic center clouds, protostellar outflows and comets, demonstrating the existence of efficient astrophysical pathways to chemical complexity. Exploring these pathways are key both to constrain the prebiotic evolution during star formation and to develop new tracers of otherwise inaccessible physical phenomena. The detected complex molecules all reside in the gas. Yet they probably form on interstellar grains, in ices that evolve with their environment and finally evaporate as the grains are heated by new-born stars or by shocks. This ice evolution is observed directly through infrared observations and indirectly through millimeter observations of evaporated ices. In this talk such observational results are combined with laboratory studies on different ice processes, especially UV photodesorption and UV induced organic chemistry, to map out the chemical evolution of ices during the pre- and proto-stellar stages of star formation. The protostellar stage is followed by the formation of a protoplanetary disk, with unique physical properties that may result in the activation new chemical pathways. I will end with showing exciting new observational results on the chemistry in protoplanetary disks, acquired within the ongoing SMA legacy program DISCS, and also some thoughts on future observational and laboratory programs to expand our knowledge of the chemical evolution during planet formation.
Feb 10 Thu, 3PM	Dr. Nick Konidaris (Caltech) *The Evolution of the ISM in "Red and Dead" Galaxies & Spectroscopic Transient Followup* Massive early-type red galaxies are considered a final product ofgalaxy evolution. Understanding the star formation history of these galaxies is tough but will necessarily yield deeper understanding of the whole process of galaxy evolution. I will discuss observations of stellar populations and the often forgotten (and hard to measure) ISM in samples of massive early-type red galaxies observed at z ~ 0.7 and z ~ 0.1. With distant galaxies as the backdrop, I will discuss the MOSFIRE spectrograph on Keck, which I am building. Here the talk diverges from galaxies and switches gears to astronomical transients. I present "the SED Machine" -- a spectrograph system designed from the ground-up to systematically classify the outrageous numbers of objects discovered by modern transient surveys using "small" telescopes. This instrument working in conjunction with on-going synoptic surveys is a powerful combination and will energize diverse astronomical fields.
Feb 18	Dr. Warren Brown (CFA) *Black Holes and Hypervelocity Stars* A massive black hole sits in the heart of the Milky Way. Oneconsequence of the black hole is that it ejects "hypervelocity stars"from the Milky Way at ~1000 km/s velocities. We discovered the firsthypervelocity star in 2005, and since then our targeted survey hasdiscovered 14 more unbound stars. The distribution of hypervelocitystars, in space and in velocity, is linked to the black hole ejectionmechanism, and reveals the history of stars interacting with the blackhole. Measuring hypervelocity star trajectories may also place uniqueconstraints on the distribution of dark matter in the Galaxy.
Feb 25	Dr. Genevieve Graves (Berkeley) *Galaxy Evolution in 3D: Mass, Dissipation, and Truncation* To zeroth order, early type galaxies form a one-dimensional family in which their observed properties— color, metallicity, environment, central black hole masses—all scale with their mass. This makes it difficult to disentangle the critical properties that determine their evolutionary history because everything correlates with everything else. Examining where this 1D sequence breaks down can provide essential clues to galaxy evolution. I present observational evidence that galaxy star formation histories form a multi-dimensional family, such that galaxies of the same mass today start out with similar star formation histories but shut down star formation ("quench") at different times. A parallel study using semi-analytic models of galaxy evolution suggests that these differences are due to their underlying halo mass assembly histories. Indeed, the observed family of galaxy star formation histories seems to be a generic result of a mass-threshold for quenching, given a standard ΛCDM paradigm that includes mass-dependent evolution and stochastic hierarchical assembly.
Mar 04	Dr. Matthew Hedman (Cornell University) *The Cassini-Huygens Mission to Saturn and Curious Corrugations in Saturn's Rings* The Cassini-Huygens mission is currently conducting an in-depth investigation of the Saturn system, and the data returned by the spacecraft have yielded many surprises that are re-shaping our understanding of the planet, its moons and its rings. This talk will focus on a recently discovered structure in Saturn's rings which indicates that about 25 years ago a broad swath of the rings suddenly became tilted out of Saturn's gravitational equator. We will explore how this might have happened, including the intriguing possibility that cometary debris may have struck the rings at this time.
Mar 11	Dr. Remy Indebetouw (University of Virginia) *Resolved Massive Star Formation in Extragalactic Molecular Clouds* Many properties of galaxies are determined by their star formation history: what masses of stars formed with what efficiency at what locations in the galaxy? Star formation rates averaged over kiloparsecs of space and 10s of megayears of time follow the tight Schmitt-Kennicutt correlation relative to the amount of available gas, but the devil and the physics are in the details. Spitzer and Herschel enabled the wide-scale study of _resolved_ star formation inextragalactic GMCs: in the Magellanic System, sub-parsec resolution allows the analysis of all individual intermediate to massive protostars. The resulting instantaneous star formation rate sometimes differs from the averaged measures. I will discuss star formation and feedback from the 30 Doradus cluster to quiescent molecular clouds to the tidally disturbed, low-metallicity Magellanic Bridge. ALMA will enable us to properly study the other half of the star-formation picture -- molecular clumps. With ALMA plus large-aperture infrared telescopes, we'll be able to extend this analysis throughout the local universe.
Mar 16 Wed, 3PM	Dr. Alyssa Goodman (Harvard University) *Making Sense of High-Dimensional Data and Visualizations* The "data deluge" in science is old news. Now, it's pouring, and we need working tools to collect, sort out, understand, and keep what is falling down on us.In astronomy, the greatest insights very often come from studies where more than one "band" of data (e.g. optical, infrared, radio, X-ray) is combined. And, data sets aren't just large--they are often also high-dimensional, in that they contain information about flux as functions not just of position on the sky, but also as functions of a third dimension (e.g. frequency, velocity), and/or of time. Life science, geophysical, and geospatial data all present similar challenges.In this talk, I will focus on examples drawn from my group's research on star formation in molecular clouds. In particular, I will show how new visualization and statistical analysis techniques relying on interactive high-dimensional views of data and on automated algorithms for "segmenting" data give new insight. "Segmentation" in imaging terms refers to extracting the meaningful structures from data, and I will show results from both dendrogram (tree-hierarchy) and machine-learning approaches. I will emphasize how the visualization of segmentation results is critical for understanding. The highlighted science results will show how we can now--for the first time--quantitatively but intuitively understand the connections between the "real" (position-position-position) space where simulations (e.g. of star formation) can be made and the "observational" (e.g. position-position-velocity) space available to earthbound astronomers. As a result of this newfound understanding, we can place important limits on the validity of virial-theorem-based calculations of the properties of gas--allowing, for example, for better estimates of which gas in star-forming regions is most likely to stay bound long enough to form stars.Even though this abstract may sound technical to non-star-formation or non-computational researchers, my goal will be to keep the talk accessible to non-experts, so people from other fields faced with high-dimensional data and visualization challenges should feel free to join in--and to ask questions!
Mar 18	Dr. Natalie Batalha (NASA Ames) *Catching Shadows: Kepler's Year-Two Transit Census* Launched in March, 2009, NASA's Kepler Mission is poised to determine the abundance of earth-size planets in the Galaxy. The project has hosted two major data releases, providing the astronomical community with four months of nearly continuous, high-precission photometry of all stars targeted as part of the Kepler planet search. A catalog of nearly 1,000 stars with transiting planet candidates, more than 70% of which are smaller than Neptune, accompanied the latest data release (Borucki et al. 2011). Ground-based follow-up observations, transit timing observations, and blend analyses have all played a major role in validating the planet interpretation, leading to major mission milestones such as the discovery of Kepler's first rocky planet, Kepler-10b, and the discovery of six transiting planets orbiting the same star, Kepler-11. Multiple transiting planet candidate systems are abundant in the released data. Dynamical studies suggest that the false-positive rate for these systems will likely be less than 10%, and the potential for determing planet masses via transit timing variations hold much promise for confirming the smallest planet candidates. I will present an overview of Kepler's recent discoveries and our progress towards the ultimate objective which is to determine the frequency of habitable, earth-size planets.
Mar 25	Dr. Eugene Chiang (UC Berkeley) *Planetesimal Formation* Planets are built from planetesimals: solids larger than a kilometer that grow by colliding in pairs. Planetesimals themselves are unlikely to form by two-body collisions alone; subkilometer objects have gravitational fields individually too weak, and electrostatic attraction is too feeble for growth beyond a few centimeters. I will review the possibility that planetesimals form when self-gravity brings together vast ensembles of small particles. I will concentrate on the classic scenario in which dust particles settle into a thin, dense sheet at the disk midplane that gravitationally fragments.
Apr 01	Dr. Dan Marrone (University of Arizona) A Close Look at Sagittarius A* The compact radio/IR/X-ray source Sagittarius A* marks the location of the Milky Way's central supermassive black hole. Investigations at all available wavelengths have shown it to be extremely under-luminous for its mass, radiating just 10^-9 of its Eddington luminosity. The physics of this faint emission and even the structure of the emitting region remain disputed, while observations intended to clarify the picture have only made it murkier. I will present a program to understand Sgr A* through observations at (mostly) submillimeter wavelengths, a special place in the spectrum where a combination of instrument capabilities and source physics allow us to study the emission just outside the event horizon. I will recount results of our efforts to date, including a surprising new polarization measurement, the questions they raise, and our prospects for resolving them.
Apr 08	Dr. Christopher Carilli (NRAO) *Radio astronomical studies of galaxy formation: the dense gas history of the Universe and the ALMA/EVLA revolution* Deep optical and near-IR surveys have traced the star formation history of the Universe as a function of environment, stellar mass,and star formation rate, back to cosmic reionization and the first galaxies (z > 6). While progress has been truly impressive, near-IR studies of early galaxies are fundamentally limited in two ways: (i) obscuration of rest-frame UV emission by dust, and (ii) near-IR studies reveal only the stars and ionized gas, thereby missing the evolution of the cool gas in galaxies, the fuel for star formation. Line and continuum studies at radio wavelengths (cm through submm) address both these issues, by probing deep into the earliest, most active, and dust obscured, phases of galaxy formation, and by revealing the molecular and cool atomic gas. I will summarize the techniques of radio astronomy to perform these studies, then present two recent examples. The first will consider the atomic and molecular gas, dust, and star formation, in the host galaxies of z ~ 6 quasars. The host galaxies are under-going extreme starbursts, with star formation rates > 1000 Mo/year, and molecular gas masses in excess of 1e10 Mo. Through gas dynamics, we can estimate the ratio of the bulge mass to black hole mass. These observations imply that we are witnessing the co-eval formation of massive elliptical galaxies, and super-massive black holes, within 1 Gyr of the Big Bang. The second entails observations of normal galaxy formation during the 'epoch of galaxy assembly' (z ~ 1.5 to 2.5). These observations reveal massive gas reservoirs without hyper-starbursts, and that active star formation occurs over a wide range in galaxy stellar mass. We find that the peak epoch of star formation in the Universe also corresponds to an epoch when the baryon content of galaxies was dominated by molecular gas, not stars. I will conclude with a description and status report of the Atacama Large Millimeter Array, and the Expanded Very Large Array. These telescopes represent an order of magnitude, or more, improvement over existing observational capabilities from 1 GHz to 1 THz, promising to revolutionize our understanding of galaxy formation.
Apr 15	Dr. Adam Leroy (NRAO) *The HERACLES and THINGS View of Gas and Star Formation in Nearby Galaxies* I will describe what we have learned about the relationship between star formation and gas in nearby galaxies from the combination of new ISM surveys (IRAM HERACLES, VLA THINGS) with shorter-wavelength literature data (SINGS, LVL, the GALEX NGS, and optical data). I will discuss the different relations among HI, H2, and star formation in galaxies, highlighting a new method to extract very sensitive CO measurements using HI priors. I will then discuss scalings between CO and star formation tracers in detail, highlighting breakdowns for low-metallicity galaxies, starbursts, and at cloud scales. Finally, I will show how variations in the H2-to-HI ratio --- which have been previously identified as a star formation threshold --- depend on environmental factors like ISM density, dust abundance, and gravitational instability.
Apr 29	Dr. Ignas Snellen (Leiden University) *The Atmospheres of Transiting Extrasolar Planets* One of the most exciting discoveries in astronomy in recent years has been the detection of planets orbiting other stars than the sun. Now, fundamental questions can be addressed about the origin and uniqueness of the solar system, and Earth in particular. While the exoplanet population is rapidly being deciphered, and the hunt for rocky Earth-like planets has begun, amazing properties about the atmospheres of the hottest exoplanets are being determined. In Leiden we are building up a strong expertise in ground-based observations - probing exoplanet atmospheres at very high spectral resolution.
May 06	Dr. Megan Eckart (NASA Goddard) *Microcalorimeter Arrays for X-ray Astrophysics: Astro-H SXS and TES Detector Development* High-resolution X-ray spectroscopy is a powerful tool for probing the high-energy Universe. We are developing instruments and detector technologies for future x-ray observatories using microcalorimeters, a type of x-ray detector designed for very high energy resolution. These instruments will enable non-dispersive imaging spectroscopy over the soft x-ray band (~0.3-12 keV), allowing spectroscopy of spatially extended sources and providing excellent energy resolution across the bandpass (<5 eV FWHM at E~6 keV). Microcalorimeters consist of an x-ray absorber, a sensitive thermometer, and a weak link to a thermal bath. The energy of a single incoming photon raises the temperature of the absorber and the resulting change is measured precisely by the thermometer before the absorber cools through the weak link. I will describe our detector arrays that utilize superconducting transition-edge sensors (TESs), a technology that can be used not only for x-ray astrophysics but for applications across the electromagnetic spectrum (e.g., for sub-mm/infrared bolometers). I will present our state-of-the-art results from kilo-pixel arrays designed for future x-ray missions (IXO?) and a novel device optimization that has achieved unprecedented spectral performance (dE=1.3 eV at 1.5 keV and 1.6 eV at 6 keV). In addition, I will discuss our upcoming flight projects, including the Soft X-ray Spectrometer for Astro-H (launch 2014) and the Micro-X Sounding Rocket Experiment.
Jun 03 Cody Hall	Dr. Jill Tarter (SETI Institute) *setiQuest - A Global Community Search for Evidence of Extraterrestrial Technologies: It Could Change The World* The 1959 Nature article by Giuseppe Cocconi and Phil Morrison provided the theoretical underpinnings for SETI, accompanied in 1960 by Project Ozma, the first radio search for signals by Frank Drake at the National Radio Astronomy Observatory (NRAO). More than 100 search programs have been conducted since that time, primarily at radio and optical wavelengths, (see http://observations.seti.org) without any successful signal detection. Some have suggested that this means humans are alone in the cosmos. But that is far too strong a conclusion to draw from far too small an observational sampling. Instead of concluding that intelligent life on Earth is unique, it is more appropriate to note that in 50 years our ability to search for electromagnetic signals has improved by at least 14 orders of magnitude and that these improvements are still occurring at an exponential rate. At the SETI Institute we are in the process of reinventing the way we search in order to fully utilize these technological enhancements. We are now building the setiQuest community and we intend to get the world involved in making our searches better. We need to find ways to harness the intelligence of all Earthlings in order to better seek out extraterrestrial intelligence. If we do it right, we just might succeed, and we might also change how we see ourselves, and make our own world a better place.
Jun 10	Dr. Jason Rowe (NASA Ames) *Photometry is the new Spectroscopy: Results from the Kepler Mission* The Kepler mission offers a special opportunity to study the nature of stars and their companions with high-precision, high-duty-cycle photometry. I will present an update on efforts to produce uniform state-of-the-art lightcurve modeling for Kepler's list of planetary candidates using tested and validated algorithms. This process involves modeling planetary transits, phase curves and orbits. These models use Kepler photometry and groundbased follow-up observations to determine bulk planetary parameters such as the radius and mass. More importantly, we will determine posterior probability distributions for the fitted parameters by employing a Markov chain Monte Carlo algorithm. By calculating detailed models of the Kepler targets, my work will measure with uncertainties: orbital periods, planet radii, inclinations, reflection/emission from the planet, the amplitude of planet-star gravitational interactions and transit timing variations. When sufficient groundbased radial velocities or asteroseismic analysis are available one can model orbital solutions and planetary densities. I will also discuss the importance of modeling multi-planet, transiting systems by fitting for each planet-candidate simultaneously. The remarkable yield of planet-candidates discovered by Kepler points towards a unique and special opportunity where a micro/nano-satellite can quickly and efficiently search the brightest stars in the sky for planetary companions. I will demonstrate how the BRITE mission will provide an opportunity to search for transiting planets around naked eye stars.
Jun 28 Tue	Dr. Guinevere Kauffmann (Max-Planck-Institut) *What can be Learned from the Atomic and Molecular Gas Scaling Relations of Nearby Galaxies?* I will present some highlights from GASS, the Galex Arecibo SDSS Survey, as well its sister survey COLD GASS. These surveys are characterizing the atomic and molecular hydrogen content of a sample of ~1000 nearby galaxies with stellar masses greater than 10^10 M_sol down to gas fraction limits of a few percent. These surveys will allow us to understand the balance between atomic and molecular gas in nearby galaxies, and how these gas properties scale with other global galaxy properties such as stellar masses and star formation rates. By combining these observations with resolved spectroscopy, our aim is to learn about the processes that regulate accretion from the external environment and ongoing star formation in the present-day galaxy population.

Last modified: 07 Sep 2011, 10:42:27

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