Astronomy & Physics
Colloquia & Current Events 2013-14
SUBJECT TO CHANGE! Be sure to check back often.
Friday January 17, 2014, 3:00pm, AT101
Tyler Desjardins, University of Western Ontario
Friday January 24, 2014, 3:00pm, AT101
Dr Casey Lambert, CSA and SMU
Friday January 31, 2014, 3:00pm, AT101
Dr Jorge Moreno, University of Victoria
Friday February 14, 2014, 3:00pm, AT101
Dr Danilo Marchesini, Tufts University
Friday February 28, 2014, 3:00pm, AT101
Dr Ted Jacobson, University of Maryland
Friday March 7, 2014, 3:00pm, AT101
Dr George Chartas, College of Charleston
Friday March 14, 2014, 3:00pm, AT101
Dr Peter Marzlin, St Francis Xavier University
Friday March 21, 2014, 3:00pm, AT101
Dr Stephanie LaMassa, Yale University
Friday March 28, 2014, 3:00pm, AT101
Dr Megan Eckart, NASA Goddard Space Flight Centre
Wednesday September 4, 3:00pm, L176
Dr Joshua M. Bray, Montana State University, Bozeman
Title: Magnetic Resonance Imaging of Complex Flow: Turbulent Rayleigh-Bénard Convection in a Supercritical Fluid
Abstract: In pragmatic terms, the general populace recognizes Magnetic Resonance Imaging (MRI) as a premiere medical imaging modality because it permits three-dimensional examination of soft tissue—in knees, spines, brains, etc.—without cutting them open or sticking things inside.
In actual fact, many things are better examined without cutting them open or sticking things inside!
As a non-destructive characterization technique, MRI has also emerged as an invaluable tool for engineering applications as diverse as functional materials, contaminant transport in geologic media, and carbon capture and storage. This talk will offer an introduction to MRI techniques aimed toward physicists and will explain how the interaction between nuclear spin and a magnetic field can yield detailed images and signal rich in information about molecular dynamics. Recent results on the application of MRI to a convecting supercritical fluid will also be highlighted, where pattern-forming dynamics and statistics of turbulent velocity fluctuations have been detected in a thermodynamic regime normally inaccessible to traditional flow measurement techniques. These measurements, in turn, provide experimental validation for emerging theories of “superstatistics” as a description of turbulence and other non-equilibrium phenomena.
Friday September 6, 10:00am, SB160
Tuesday, September 10, 2013, 2:30 - 3:00 pm, AT 305
MSc Defence: Christopher Cooke
Title: Upper Boundary Condition for Asteroseismological Modelling of Solar-type Stars
Abstract: In asteroseismology, improper modelling of the near-surface layers of stars has led to a well known disagreement between observed and computed oscillation frequencies. We present a grid of line blanketed spherical LTE model atmospheres and high resolution extinction spectra for use in interpolating an accurate outer boundary condition for asteroseismology calculations at arbitrary Teff and log g. We investigate the accuracy of four interpolation methods by interpolating among our grid to solar values of Teff and log g and comparing the results to an exact solar model. We test the impact of the resolution of our grid on the accuracy of the interpolations by perform linear interpolations among our grid at different sampling rates in Teff and log g. We test whether interpolating κR within our grid and computing τR or calculating τR for each model and interpolating it directly produces more accurate results. We also present a NLTE exact solar model and compare the boundary condition resulting from it to those of the LTE exact model. We find that quadratic and linear interpolation methods produce comparable results, that interpolation by cubic splines produces the best results, and that least-squares quadratic interpolation produces results of least accuracy. Increasing the sampling rate in log g by a factor of 3 was found to double the accuracy of interpolations within our grid, while increasing the sampling rate in Teff by a factor of 6 was found to improve the accuracy of interpolations by a between a factor of 1.25 and 1.5. Pre-calculating τR for each model and interpolating among the grid was found to be more accurate than interpolating κR among the grid and computing τR. We also find that the photosphere in the NLTE exact solar model is situated at a lower optical depth than in the LTE exact solar model.
Friday September 13, 3:00pm, AT101
Dr Chia-Ying Chiang, Saint Mary's University
Title: Modelling the X-ray Spectra of Accreting Black Holes
Abstract: X-ray emission from accreting black hole systems provide information on the accretion geometry of the innermost region of the black hole. Observational evidence indicates that black hole systems are consisted of an accretion disc around a central black hole with a hot illuminating corona above the disc plane. The resulting X-ray spectra can be decomposed by a powerlaw continuum, a reflection component and a thermal disc component if the accretion is hot. The reflection features (i.e. the 6.4 keV Fe K-alpha fluorescent line, the Compton hump) are frequently observed in the X-ray spectra of accreting black holes and can provide information on the black hole spin. This talk mainly focuses on modelling the X-ray spectra of accreting black holes, including black hole binaries (BHBs) and active galactic nuclei (AGN). The reflection model has been tested on sources with various masses and properties. I started by re-examining the XMM-Newton spectrum of the black hole candidate XTE J1652-453 and found that a self-consistent relativistic reflection model works well. The scenario was then applied on more massive objects, the Type 1 AGN. The analyses of these sources again reveal the importance of disc reflection. The large soft excess displayed in the spectrum of CBS 126 can be successfully explained by blurred reflection. The complex spectrum of MCG-6-30-15 can be modelled by a model consisting of several absorbing zones, together with a relativistically blurred reflection component. The relativistic reflection model works well on data from all epochs and explains both the spectral and timing properties without difficulty, and partial-covering absorbers are not required in all analyses.
Friday October 18, 3:00pm, AT101
Dr Marcin Sawicki, Saint Mary's University
Title: Life and Death at Cosmic High Noon
Abstract: Galaxies are giant machines that turn gas into stars and the rate at which they were doing this was highest around redshift z=2, when the universe was only 1/4 of its present age. This is "cosmic high noon", and I will discuss both starforming (live) and quiescent (dead) galaxies at z~2. My choice of this live/dead terminology here is not just a fanciful analogy but is central to my talk: I will show how the starforming-to-quiescent transition follows rules that are very similar to those that govern human death, leading not only to a well-justified "live/dead" terminology for star forming and quiescent galaxies, but to a simple and direct explanation for the Schechter-like stellar mass function for massive galaxies along with potential insights into the quenching mechanism itself.
Friday October 25, 10:30am, AT305
Mr. Esteban Castro, Universidad Nacional Autuónoma de México
Title: On the behavior of entanglement in systems of massive particles under relativistic transformations
Abstract: We analyze the entanglement change, as seen by different relativistic observers, for a system consisting of two spin-1 particles, considering different partitions of the Hilbert space, which has spin and momentum degrees of freedom. We show that there exists a complete set of states of the spin subspace in which the entanglement change of any state in the set is zero for all partitions and all values of the Wigner angle. Moreover, these states only change by a global phase factor under the Lorentz boost. Within this basis, maximally entangled invariant states, interesting for quantum information purposes, are explicitly obtained. On the other hand, the entanglement in the particle-particle partition is Lorentz invariant, thus protecting the consistency of quantum correlations and teleportation results. We show how our results may be generalized to arbitrary spin.
Friday October 25, 3:00pm, AT101
Dr Aldona Wiacek, Saint Mary's University
Title: Applying Physics to Air Quality and Climate Problems
Abstract: Desert dust is the most abundant aerosol species in the atmosphere and it is also the most efficient ice nucleating material, commonly found in the ice crystal residuals of cirrus and mixed-phase clouds. While dust source regions are increasing due to human activity, it is difficult to measure or model the concentration of dust particles in the upper troposphere with the certainty necessary for global modeling of clouds and their radiative effects on climate. In this talk I will discuss my work on the Lagrangian transport modeling of mineral dust, as well as on the challenges of measuring this aerosol species remotely from space. Finally, I will outline my plans for a Tropospheric Remote Sensing Laboratory at Saint Mary’s University.
Friday November 1, 3:00pm, AT101
Dr Toru Yamada, Tohoku University
Title: WISH: Wide-field Imaging Surveyor for High Redshift
Abstract: WISH, Wide-field Imaging Surveyor for High-redshiftt, is a space mission concept to conduct very deep and wide-field surveys at near infrared wavelength at 1-5μm to study the properties of galaxies at very high redshift beyond the epoch of cosmic reionization. The concept has been developed and studied since 2008 to be proposed for future JAXA/ISAS mission with international collaboration now being developed. PRIMARY SCIENTIFIC GOALS of WISH are to search for the most-distant first-generation galaxies and revealing the galaxy distribution and properties in the era of cosmic re-ionization, to study of the expansion history of the universe and properties of dark energy by using a very large sample of high-redshift Type-Ia Supernovae, and to conduct extensive study in many other field of astronoy utilizing the unique wide-area NIR observations from space.
WISH has a 1.5m-diameter primary mirror and a wide-field imager covering 850 arcmin2. The pixel scale is 0.155 arcsec for 18μm pitch, which properly samples the diffraction-limited image at 1.5μm. The main program is Ultra Deep Survey (UDS) covering 100 deg2 down to 28AB mag at least in five broad bands.
We expect to detect >>10^4 galaxies at z=8-9, 10^3-10^4 galaxies at z=11-12, and 50-100 galaxies at z>14, many of which can be feasible targets for deep spectroscopy with Extremely Large Telescopes. With recurrent deep observations, detection and light curve monitoring for type-Ia SNe in rest-frame infrared wavelength is also conducted, which is another main science goal of the mission. During the in-orbit 5 years observations, we expect to detect and monitor >2000 type-Ia SNe up to z~2. WISH also conducts Ultra Wide Survey, covering 1000deg2 down to 24-25AB mag as well as Extreme Survey, covering a limited number of fields of view down to 29-30AB mag.
In this talk, we introduce the basic capability of WISH and examples of science applications as well as reporting the current status of the development of the base-line design model.
Friday November 8, 3:00pm, AT101
Dr David Radford, Oak Ridge National Laboratory
Title: The Nature of Neutrinos
Abstract: First hypothesized by Wolfgang Pauli in 1931, the elusive neutrino is an electrically neutral elementary particle that interacts only very weakly with matter. Produced in copious amounts in nuclear reactions and radioactive decays, neutrinos play key roles in the state of the early universe, in cosmology and astrophysics, and in nuclear and particle physics. In the 1970's and 80's, an experiment a mile underground in a gold mine in South Dakota measured the flux of neutrinos from the Sun’s core. It detected only about one-third of the neutrinos predicted by theory, and ultimately led to a much deeper understanding of particle physics. The current status of neutrino experiments will be reviewed, and a new experiment under construction in that same SD gold mine will be described. This experiment aims to show that the neutrino and its antiparticle (the anti-neutrino) are in fact the same particle.
Friday November 15, 3:00pm, AT101
Dr Nancy Evans, CfATitle: Cepheids, Binaries, and Star Formation: Making the Connection
Abstract: Cepheids provide insight into both star formation and stellar evolution. Multiwavelength studies supply binary/multiple properties for these reasonably massive stars, which allow the exploration of differences between high and low mass stars formation. A 3 part program to derive binary parameters is underway. We are conducting a survey of Cepheids with the Hubble Space Telescope Wide Field Camera 3 (WFC3) to identify possible resolved companions, for example Eta Aql. X-ray observations (Chandra and XMM-Newton) can confirm whether possible low mass companions are young enough to be physical companions of Cepheids, hence providing constraints on star formation. In a related study of intermediate mass stars, Chandra X-ray observations of late B stars in Tr 16 have been used to determine the fraction which have low mass companions (which are X-ray active in contrast to the late B stars which are X-ray quiet). Finally, velocity data from the Groynya, et al. is being combined with CORAVEL data develop statistics on long period orbits.
Friday November 22, 3:00pm, AT101
Dr Gerard van Belle, Lowell Observatory
Title: Directly Determined Linear Radii, Effective Temperatures, and Shapes of Stars from Long-Baseline Optical Interferometry
Abstract: A brief introduction to the concepts of long-baseline optical interferometry (LBI) will be presented, followed by a review of fundamental stellar parameters as directly determined using LBI. Special attention will be paid to the progression of precision over the years of the observables of linear radius and effective temperature, with the current state-of-the-art measures approaching sub-percent levels for hundreds of stars (and being limited primarily by the ancillary data products of distance and bolometric flux, not measured angular size). Discussion will also be presented on the diminishing meaning of these gross parameterizations of stellar atmospheres, as higher-order surface details such as shapes, limb darkening, gravity darkening, and spotting are beginning to be imaged with LBI.
Friday November 29, 3:00pm, AT101
Dr Kamil Bradler
Saint Mary's University
Title: Perfect retrieval of quantum information from black holes
Abstract: Black hole information puzzle is a longstanding open problem concerned with the fate of information thrown into the black hole. In this talk, I will introduce the problem and reformulate it in the language of quantum information theory. I will argue that this is the right branch of physics to finally settle the whole issue. Quantum information theory takes the inspiration from computer science and Shannon's theory of communication and offers a new perspective on certain fundamental problems in physics. The black hole information puzzle is the most prominent example. It is really a quantum communication problem and as such it could not had been resolved before the era of quantum information theory - only now we have the right tools at our disposal.
Previous Years' Abstracts