University of Toronto Astronomy Colloquia



	ASTRONOMY COLLOQUIA

First half of 2003

Jan 15 Wed., 2:00PM! MP 203!	Dr Marc Kuchner (CfA) *Reading the resonant signatures of planets in debris disks* A planet in a circumstellar dust cloud often carves an easily visible signature in the dust density via orbital resonances. This pattern can point to the planet and reveal its orbit even when the planet itself is much too faint to see. I will paint an overview of the variety of resonant structures a single planet on a moderately eccentric orbit can create in an optically thin dust disk and compare the resonant geometries found in the solar zodiacal cloud with observations of debris disks around Vega, Epsilon Eridani and Fomalhaut. Host: Marten van Kerkwijk
Jan 17	Dr Stefanie Mühle (Bonn) *The Starburst in the Dwarf Galaxy NGC 1569: What did it do to the interstellar gas?* The dwarf galaxy NGC 1569 has experienced a tremendous starburst until about 5 million years ago. Using new and unpublished high-resolution observations, I discuss the distribution and the properties of the molecular and the atomic interstellar gas and show how Galactic foreground emission affects the analysis of the single-dish and the interferometric observations of the neutral atomic hydrogen in NGC 1569. The starburst has had a strong impact on the distribution and the kinematics of the atomic gas. The molecular gas distribution has been influenced by violent star formation, too, resulting in peculiar line ratios. Our results are compared to corresponding data of the H-alpha emission. I also show a new, very sensitive map of the H I halo and discuss the possible origin of its structure. Host: Ernie Seaquist
Jan 24	Prof. Jaymie Matthews (UBC) *The MOST space photometry mission: All systems go for launch* Host: Slavek Rucinksi
Jan 31	Prof. Ue-Li Pen (CITA) *Weighing the Universe with Weak Lensing* Weak gravitational lensing provides a direct statistical measure of the dark matter distribution. The variance is easiest to measure, which is degenerate in the matter density and the amplitude of fluctuations. The degeneracy is broken by measuring the skewness arising from the fact that densities must remain positive, which is not possible when the initially symmetric perturbations become non-linear. Skewness measures the non-linear mass scale, which in combination with the variance measures Omega directly. We present the first detection of dark matter skewness from the Virmos-Decart survey. We have measured the full three point function, and its projections onto windowed skewness, and discuss their implications for the matter density of the universe. Host: Marten van Kerkwijk
Feb 7	Dr Katya Verner (GSFC) *What makes Fe II spectra strong in astrophysical plasmas?* Many objects in our Universe - from stars to quasars - exhibit rich Fe II emission spectra. Often it is unclear whether iron abundance or radiative pumping by a strong radiation field is the dominant mechanism that properly explains the unusual strength of Fe II in these objects. A correct answer would have direct implications on the chemical evolution of our Galaxy and the Universe. We will present a new Fe II excitation model and apply it to the vicinity of the Eta Carinae Nebula, which is uniquely rich in strong Fe II and [Fe II] lines. The central source(s?) is known to be an unusually strong radiative source, with a luminosity intermediate between the sun and a weak quasar. Our model reproduces the intensities of the Fe II and [Fe II] lines under a variety of excitation conditions and reveals many new details on the physics and origin of Fe II lines in astrophysical plasmas. We intend to apply the new Fe II excitation model to high redshift quasars to determine iron abundances in earlier epochs. Host: Peter Martin
Feb 12 Wed., 1:30PM! MP 203!	Dr Henk Hoekstra (CITA) *The hunt for the equation of state of the universe* The recent discovery that the dynamics of the universe are dominated by some "dark energy" has created much excitement and puzzled physicists. Although many different mechanisms have been proposed to explain the results, current observational constraints to distinguish between various models are limited. The key parameter to be determined over the next decade is the equation of state w=P/rho, which relates the pressure and the energy density of the dark energy. I will discuss three techniques that can be used to constrain this parameter. The type Ia supernovae and weak lensing measurements will use data from the upcoming CFHT Legacy Survey, whereas the RCS2 cluster survey uses the abundance of massive clusters to constrain cosmological parameters. To support the feasibility of these techniques I will discuss some recent results obtained using data from the RCS1 cluster survey. Host: Ray Carlberg
Feb 21	Dr Ben Oppenheimer (AMNH) *The Lyot Project* Recent advances in optical techniques, technologies and the ability to detect exoplanets indirectly have consipired to convince the majority of astronomers that a new field of exoplanetary science is on the verge of maturity. Within the next two decades not only will exoplanets be studied much the way remote observations reveal features of Jupiter and Saturn, but we may have solid evidence for habitable planets within the solar neighborhood. The Lyot Project, a new instrumentation effort based at the American Museum of Natural History, is poised to make advances toward these goals. I will describe the project, it's innovations and provide a detailed description of predicted scientific performance. Host: Marten van Kerkwijk
Feb 24 Mon., 3PM! MP 203!	Dr Mike Gladders (Carnegie, Pasadena) *Extreme Clusters in the Red-Sequence Cluster Survey* The Red-Sequence Cluster Survey (RCS) is a ~100 square degree imaging survey designed to locate and characterise galaxy clusters to redshifts as high as 1.4. After a brief description of the complete survey and some of the original RCS results, I will focus the rest of this talk on recent results coming primarily from 8m-class telescope followup of the cluster sample. In particular, I will discuss two "extreme" cluster subsamples: clusters with arcs due to strong lensing of background sources, and clusters at very high redshifts. The strong lensing clusters provide an unambiguous detection of evolution in the RCS sample, and demonstrate that a previously unrecognized sample of "super-lenses" must exist. The high-redshift clusters are particularly powerful for studying the formation epoch and formation process of early-type galaxies; like previous smaller studies, the RCS results indicate that the stars in early-type galaxies formed synchronously very early in the universe. Host: Howard Yee
Feb 26 Wed., 1:30PM! MP 203!	Prof. Dimitar Sasselov (CfA) *Extrasolar Giant Planets and their Parent Stars* The talk will summarize some of the unusual features of planets and planetary systems discovered recently around nearby stars. Our focus will be on the close-in giant planets and the clues they hold for theory of structure and modes of formation. Our study of the new transiting giant planet, OGLE-TR-56b, is placing interesting constraints. Host: Norm Murray
Mar 4 Tue, 3PM!	Prof. Anneila Sargent (Caltech and Neil Graham Visiting Lecturer, University College) *Observations of Protoplanetary Disks* Planetary systems have their origins in the circumstellar disks that are associated with the earliest stages of star formation. The morphologies, extents, and masses of these disks are generally compatible with the properties anticipated for planet-forming environments and there is some evidence for larger accumulations of dust grains in older disks, suggestive of planetesimals formation. The kinematic properties of the circumstellar material are also compatible with planetary system formation. However, many details of the path from the protostellar to protoplanetary disks, and from there to the actual formation of planets remain unclear. Survival time scales for disk gas and dust present problems for some theories of planet formation and only limited information on the chemical evolution of the disks is available. Relevant observations will be presented and the implications discussed. Host: John Percy
Mar 5 Wed., 1:30PM! MP 203!	Dr Sunil Golwala (Caltech) *Cosmological Science with the Sunyaev-Zeldovich Effect and Bolocam* The Sunyaev-Zeldovich effect - the scattering of the cosmic microwave background by hot electrons in galaxy clusters and other large-scale structure - is beginning to open a new window for cosmological observations. SZ effect measurements will have an impact on our understanding of the global energy density of the universe as well as on large scale structure. New instruments coming online now and in the near future will revolutionize this field. One such instrument is Bolocam, a millimeter-wave camera being commissioned for use at the Caltech Submillimeter Observatory. We describe the instrument and present the current status of analysis of an initial blank-field SZ survey at 2.1 mm wavelength, as well as commenting on other Bolocam science topics and the more distant future for SZ instrumentation and surveys. Host: Barth Netterfield
Mar 14	Prof. Dong Lai (Cornell) *Radiation from Strongly Magnetized Neutron Stars* The study of thermal radiation from isolated neutron stars (including radio pulsars, radio-quiet neutron stars and magnetars) can provide important information on the interior physics, magnetic fields, surface composition and other properties of neutron stars. The new generation of X-ray telescopes are bringing great promise to such study. Understanding the properties of matter and radiation in strong magnetic fields is essential for the proper interpretation of the current and future observations. I will review some of the novel properties of matter and radiative transfer in strong magnetic fields. I will discuss the surprising effect of strong-field QED on the radiation spectra from magnetars. I will also discuss the polarization signatures of neutron star X-ray emission, and the prospect of using X-ray polarimetry to test fundamental physics in strong magnetic fields. Host: Marten van Kerkwijk
Mar 21	Prof. Sterl Phinney (Caltech) *Physics and Astronomy with LISA (Laser Interferometer Space Antenna)* The NASA/ESA Laser Interferometry Space Antenna (LISA), planned for launch in 2010 (with a test mission scheduled for 2006) will detect and measure gravitational radiation from astronomical sources at frequencies 0.0001 Hz to 0.1 Hz (compared to 30-1000 Hz for ground-based detectors like LIGO). LISA will detect continuous signals from: thousands of exotic binary stars in the Milky Way, merging supermassive black holes in the nuclei of merging galaxies at redshifts from 0 to 100, and compact stars scattered into supermassive black holes. The latter will provide precision tests of strong-field predictions of relativity, such as the No-Hair Theorem and energy extraction from rotating black holes. We will describe the principles of operation of LISA, and the known and unknown physics, astrophysics, and signal-processing which govern the sources it will detect and the information we will gain. Host: Marten van Kerkwijk
Mar 28	Prof. Edward Guinan (Villanova) *The Young and Restless Sun: Effects of the Young Sun's Strong Magnetic Activity on Paleo-Planetary Atmospheres and the Evolution of Life* Studies of young solar proxies (G0-G5 V stars) as part of the "Sun in Time" program, show that the young Sun was rotating over 10x faster than today. As a consequence of this, these young solar-type stars, and the young Sun, had vigorous magnetic dynamos and correspondingly strong coronal X-ray and chromospheric far-UV and UV emissions up to several hundred times stronger than those observed for the present Sun. Also, observations of the youngest solar proxies, indicate that the young Sun had frequent and powerful flares. The results of the recent study of the astrospheres of nearby stars (which correspond to the solar heliosphere), indicate that the young Sun may have had strong, massive winds that were hundreds or even thousands of times more massive than today. In this talk I will discuss the results of the "Sun in Time" program and discuss some of the major effects that the young Sun's strong magnetic activity may have had on the photoionization, photochemistry, and erosion of paleo-planetary atmospheres. Some examples that will be briefly discussed include: the possible erosion of Mercury's mantle, loss of water on Mars and the oxidation of its surface, hydrodynamic mass loss from paleo planetary atmospheres, and the evolution of the Earth's atmosphere and the origin and evolution of life on Earth (and maybe on Mars). Host: Christine Clement
Apr 4	Dr Nahum Arav (CASA, Colorado) *Exciting Times for Studying AGN Outflows* I will review the rapidly advancing field of AGN outflows, and show the progress made possible by the new generation of UV and X-ray space telescopes, as well as ground based observatories. Host: Yuri Levin
Apr 11 Refresh- ments: MP 110	Prof. Andrei Linde (Stanford) *Inflation, Dark Energy, and M-theory* I will discuss recent attempts to describe inflation of the universe and dark energy in the context of M-theory. I will argue that in accordance with the M-theory, the present stage of acceleration of the universe cannot last indefinitely long: The universe can be either in a metastable de Sitter state with an exponentially large but finite decay time, or in an unstable state with the lifetime comparable with the present age of the universe. Host: Lev Kaufman
Apr 18	No colloquium: Good Friday
Apr 25 MP 137!	Prof. Steven Shore (IUSB) *Turbulence: A Brief Guide for the Perplexed* Host: Tom Bolton
May 2	No colloquium: Cancelled
May 9 MP 137!	Prof. Marc Pinsonneault (Ohio State) *Accretion Disks and the Origin of Stellar Rotation* Stellar rotation is the single most important physical effect not traditionally included in theoretical models of stellar structure and evolution. There is a growing recognition that rotation may generate phenomena such as internal mixing with important consequences for stellar evolution. A wide range in stellar rotation rates at fixed mass and age is observed, which also implies that a range of extra mixing rates at a given mass is to be expected. The initial angular momentum of stars is closely related to the star formation process, and understanding the origin of this range is an important research topic. In this talk I begin by reviewing the theoretical framework for the origin of stellar rotation. I then turn to the observational data for low mass stars. I argue that the current data is consistent with an emerging picture where magnetic coupling between the protostellar accretion disk and the protostar governs the stellar rotation rate. In this picture the range of rotation rates prior to the T Tauri phase is generated by a range of mass infall rates; this distribution is further modified by subsequent magnetic coupling to accretion disks for varying lifetimes. Host: Slavek Rucinski
May 14 Wed., MP 137!	Damien Le Borgne (IAP) *X-ray to near-IR modeling of galaxy evolution* With the new generation of instruments on large telescopes, high quality observations become available at many wavelengths. Models are now required to interpret, at the same level of details, photometry and high resolution spectra. PEGASE is a code developed at the IAP (France), aimed at modeling the spectro-photometric evolution of galaxies. I will present the low-resolution modeling of spectral energy distributions from far-UV to near-IR, and recent improvements at very high resolution (R=10000) in the optical. New spectral indices useful to reduce the observed degeneracy between metallicity and age in stellar populations will be discussed. In addition to tracers of metallicity, age and star formation history available in UV-optical-NIR spectra, complementary powerful tracers exist in X-rays. I will describe a modeling of X-ray emission from normal and active galaxies, consistently with the modeling of optical emission. Comparisons of models and observations at high redshift will be discussed. Host: Bob Abraham
May 16 MP 137!	Dr Davy Kirkpatrick (IPAC) *The Role of Gravity and Metallicity in Shaping M, L, and T Dwarf Spectra* For main sequence stars, the main parameter controlling the appearance of the emergent spectrum is its temperature. Now that the first step at defining L and T dwarf classifications has been done, we can address whether these strictly morphological types are also primarily dictated by temperature or if another parameter such as dust also plays a role. The spectra of a few oddball L and T dwarfs will also be shown and compared to the standard sequence to demonstrate what we believe are low-metallicity brown dwarfs from a very early epoch of star formation in the Milky Way. Lastly, we will compare M and L dwarf spectra from star clusters of varying ages to show the effect of gravity on brown dwarf spectra, diagnostics from which can be used to age-date field brown dwarfs where no other info is known. Host: Bob Garrison
May 21 Wed., MP 137!	Dr Patrick Hall (Princeton/P. Univ. Catolica de Chile) *Red Quasars* Quasars have intrinsically blue spectra, which makes them easy to locate and study. But heavily obscured active galactic nuclei are also known to exist, in the form of radio galaxies or Seyfert 2s with broad lines seen in polarized light, for example. In between these extremes we should find a population of dust-reddened quasars. I discusss recent results on such quasars, primarily from the Sloan Digital Sky Survey. In a sample of 4576 SDSS quasars, 6% appear to be moderately dust reddened. More than just dust reddening may also be at work in such quasars, because they have narrower Balmer lines than unreddened quasars, as well as other spectral differences. In summary, the color distribution of SDSS quasars contains information on the distribution of reddenings around quasars, which determines the relative contributions of unreddened, moderately reddened, and obscured quasars to the total population of luminous AGN. Host: Howard Yee
May 23 MP 137!	Dr John Steele (UoT) *Eclipse Prediction and the Length of the Saros in Babylonian Astronomy* Cuneiform tablets recovered from archaeological sites in Iraq reveal that Babylonian astronomers of the first millennium BC undertook a detailed programme of regular astronomical observation. From these observations they developed complex mathematical methods for calculating astronomical events such as the visibility of the lunar crescent, the dates and celestial longitudes of planetary phenomena, and the occurrence of eclipses of the sun and moon. These astronomical methods, which were purely arithmetical, were just as effective as the later Greek geometrical theories of Ptolemy. In this talk I will explore one aspect of this Babylonian mathematical astronomy, namely the methods used to predict eclipses of the sun and moon. At the heart of these methods is the so-called Saros cycle of 223 lunar months. The variable length of the Saros, due to lunar and solar anomaly, was one of the central problems of Babylonian lunar theory, and they developed elegant techniques to separate out the lunar and solar components. Host: Marten van Kerkwijk

Last modified: 12 Dec 2003, 16:01:34
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