Department of Astronomy & Physics

Colloquia & Current Events 2015 - 2016

Colloquia Abstracts
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Archived Colloquia 2015-16

Archived Colloquia 2014-15

Archived Colloquia 2013-14

MUSCLES: Exploring the High Energy Radiation Environments around Typical M Dwarf Exoplanet Host Stars

Speaker: Dr. Alexander Brown (CASA, Univ. of Colorado)
Time: June 30, 2017 - 11:00 AM
Location: Atrium 305


The ever-growing pace of exoplanet discovery has provoked a serious need for a much better understanding of the properties of exoplanet host stars, particularly in the various manifestations of stellar activity that can influence planetary habitability. In this talk I shall discuss how host stars influence exoplanet atmospheres and even the existence of such atmospheres, using ultraviolet and X-ray data obtained by our HST Treasury project “MUSCLES” (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems”). We observed a sample of 11 K-M host stars with habitable-zone planets that were deemed to be relatively old “inactive” stars but find that the radiation and particle fluxes produced by their stellar magnetic activity are large enough to significantly affect their planets. Full spectral irradiance distributions have been produced for all the stars in the sample to aid exoplanet atmospheric modelers. I conclude by looking forward to how we can prepare better for future studies of such stars and their planets.


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2017 CAP lecture - Colliding Black Holes and Gravitional Waves: Seeing the Universe through Bizarre Messengers

Speaker: Harald Pfeiffer (CITA, University of Toronto)
Time: March 30, 2017 - 4:00 PM
Location: Sir James Dunn Building, Room 101, Dalhousie University


A century ago, Albert Einstien put forth ideas that led to two astonishing predictions.  The first prediction is black holes, regions of space with such intense gravity that nothing can escape, not even light or the strongest rockets.  The second prediction is gravitational waves, the tiniest ripples in space and time itself travelling through the universe.  Just one year ago, these fantastic ideas were confirmed by direct observations of gravitational waves by the LIGO Scientific Collaboration.  The waves observed so far were all created by colliding black holes.  In this talk, Prof. Pfeiffer will introduce black holes and gravitational waves.  He will then trace the story of the remarkable first gravitational wave discoveries, and explain how gravitational waves are now used to explore our Universe.


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Constraining the accretion regions of meteorites via astrochemical modelling of protoplanetary disks

Speaker: Dr. Jon Ramsey (Natural History Museum of Denmark and Niels Bohr Institute, University of Copenhagen)
Time: March 24, 2017 - 3:00 PM
Location: Atrium 101


Meteorites are the best available empirical record of the formation and early evolution of our Solar System. They originate from asteroid-sized parent bodies (i.e. planetesimals) that have experienced an energetic collision, ejecting material into interplanetary space. While roughly thirty thousand meteorites have so far been discovered on Earth, the meteoritic record remains very far from complete. Indeed, in many cases, interpretation of meteorite data is degenerate in regards to space and time. In this talk, I will present astrochemical and radiative transfer models of protoplanetary disks which I am using in an attempt to break this degeneracy, and constrain the accretion epoch and location of meteorite parent bodies. Through the inclusion of molecular ices and isotopologues of hydrogen and nitrogen in my models, it is possible to make direct comparisons with meteoritic data, and therefore make inferences about parent body accretion and our early Solar System.


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Blue Stragglers Stars in Open Clusters

Speaker: Giovanni Carraro (Universita’ di Padova)
Time: February 3, 2017 - 3:00 PM
Location: Sobey 260


I will report on the status of an ongoing project aimed at identifying and characteriseblue stars in open cluster.  We are conducting a spectroscopic survey with FLAMES@VLT to derive multiple epoch radial velocity for blue straggler star candidates.  The talk will focus on the motivations and the preliminary results.


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POSTPONED until fall17: Dark Matter Substructure: Cosmological Treasure Trove or a Pandora's Box?

Speaker: Frank C. van den Bosch (Yale)
Time: January 20, 2017 - 3:00 PM
Location: Atrium 101


Hierarchical structure formation in a LCDM cosmology gives rise to virialized dark matter halos that contain a wealth of subtructure.  Being able to accurately predict the abundance and demographics of dark matter subhaloes is of paramount importance for many fields of astrophysics: gravitational lensing, galaxy evolution, and even constraining the nature of dark matter. Dark matter substructure is subject to tidal stripping and tidal heating, which are highly non-linear processes and therefore best studied using numerical N-body simulations. Unfortunately, as I will demonstrate, state-of-the-art cosmological simulations are unable to adequately resolve the dynamical evolution of dark matter substructure. They suffer from a dramatic amount of artificial subhalo disruption as a consequence of both inadequate force softening and discreteness noise amplification in the presence of a tidal field.  I discuss implications for a variety of astrophysical applications, and briefly discuss potential ways forward.



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Probing relativistic effects in the central engine of AGN

Speaker: Dr. Mario Sanfrutos (Centro de Astrobiologia, ESAC (ESA))
Time: January 13, 2017 - 3:00 PM
Location: Atrium 101


Active Galactic Nuclei are perfect laboratories to check General Relativity effects by using Broad Line Region clouds eclipses to probe the innermost regions of the accretion disk and their vicinity. We are working on a new relativistic X-ray spectral model for X-ray eclipses, involving different observables including the X-ray emitting regions size, the emissivity index, the cloud's column density, ionization, size and velocity, the black hole spin, and the system's inclination with respect to our line of sight. I will present some theoretical predictions on these observables as unveiled in XMM-Newton simulations, and also show the big potential of our relativistic model to fit real data. Specifically, this model is fit to actual XMM-Newton data from a long observation of the NLS1 galaxy SWIFT J2127.4+5654, in which a Broad Line Region cloud eclipse was characterised from a non-relativistic prespective in a previous work.



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Diving into the midst of galaxies: Multiple ways of suppressing star-formation

Speaker: Dr. Thibaud Moutard (Saint Mary's University)
Time: December 2, 2016 - 3:00 PM
Location: Atrium 101


The fact that galaxies can be classified according to their star-formation activity into a blue/star-forming population and a red/quiescent population is now well established, and this bimodality, clearly observed to redshift z ~ 4, is the statistical expression of a fairly rapid phenomenon called quenching

The processes that are involved in such quenching of star formation are, however, still a matter of debate. In particular, the quenching mechanism(s) that turn star formation off in young/low-mass galaxies may be quite different from those that are at play in massive galaxies after billion years of star formation.

I will discuss the existence of two different quenching channels that contribute strongly to the shaping of the quiescent galaxy population at z < 1.5: a slow quenching channel followed by old/massive star-forming galaxies and a rapid quenching channel followed by young/low-mass ones. I will finally conclude with a review of the most promising leads regarding the physical mechanisms that may underlie these quenching channels.


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The Evolution of Quasars with Cosmic Time

Speaker: Dr. Michael Strauss (Princeton University)
Time: October 14, 2016 - 3:00 PM
Location: Atrium 101


While the luminosity and mass distributions of quasars have evolved dramatically with cosmic time, the physical properties of quasars of a given luminosity are remarkably independent of redshift.  I will describe recent results on the spectra of luminous quasars, the dark matter halos in which they sit, and the intergalactic medium of their host galaxies, that are essentially indistinguishable from moderate redshifts to z>6.    Dust obscuration is another theme in quasar studies; an appreciable fraction of the growth of black holes may be hidden at optical wavelengths by dust.  I will describe searches for obscured quasars at high redshift and low, and studies of their demographics and physical properties.  I will conclude the talk with a discussion of future surveys, including the next generation of wide-field imaging and spectroscopic surveys with the 8.2-meter Subaru Telescope.


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Undergrad Symposium

Speaker: Undergrad Research Assistants
Time: September 9, 2016 - 1:00 PM
Location: Sobey 265


OpenStars: More fun in the new world

Speaker: Dr. Ian Short (Saint Mary's University)
Time: September 16, 2016 - 3:00 PM
Location: Atrium 101


This presentation and web-app demonstration will be less technical than a typical astronomy colloquium and is appropriate for a more general audience interested in scientific computing web applications.  The current goal of the OpenStars project is to deploy a general, open-ended stellar atmospheric, spectrum, and exo-planetary system modelling and visualization code as an open source web application, and to implement the modelling in a way that is rapidly responsive on common-place low performance personal computing devices.  GrayStar implements the core physical modeling in client-side JavaScript and has been developed significantly since it was last presented at SMU.  GrayStarServer implements the core physical modeling in server-side Java and performs spectrum synthesis based on a comprehensive atomic line list.  In both cases the user interface (UI), post-processing, and visualization are implemented in JavaScript and in HTML5, feature intuitive renderings of direct observables, and will work on any web browser on any platform.  These apps serves as public virtual science exhibits, and as pedagogical apparatus for properly physics-based parameter perturbation experiments and demonstrations is stellar astronomy and astrophysics.  As a pure JavaScript deployment, GrayStar turns any web browser into a computational astrophysics lab through the developer console, and entices students to contribute to the project on their own initiative.  I will perform a variety of pedagogically crucial demonstrations with both apps.   Both the physics engines and the UIs are suitable for indefinite further development at the undergraduate, graduate, and PDF level in astronomy and in computing science.   See .


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Galactic Archaeology Near and Far: Using Chemical Abundances of Globular Cluster Stars to Probe Galaxy Formation

Speaker: Dr. Charli Sakari (University of Washington)
Time: September 30, 2016 - 3:00 PM
Location: Atrium 101


Globular star clusters (GCs) are found around nearly every galaxy in the local universe.  GCs are thought to form in every major burst of star formation, and they are expected to follow the properties of a galaxy's field stars (those stars that are not in clusters).  Observations of GCs can therefore be used to unravel a galaxy's assembly history, including when and where a GC may have formed (e.g., in a dwarf galaxy that was later accreted by a larger galaxy).  In this talk I will review the techniques that are used to observe GCs, focusing on spectroscopic techniques that provide detailed chemical abundances of GC stars.  I will discuss applications to GCs in the Milky Way Galaxy and beyond, focusing on the GC population of the Milky Way's nearest massive galaxy, M31.  I will present detailed abundances from optical and infrared high resolution spectroscopy and discuss what these
abundances reveal about M31's assembly history.  The wider importance of these results for cosmology and fundamental physics will then be discussed.


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At the Edge: Recent Highlights from the Frontier Fields Program

Speaker: Dr. Gabriel Brammer (Space Telescope Science Institute, Baltimore, MD) 
Time: October 7, 2016 - 3:00 PM
Location: Atrium 101


The Frontier Fields Program has recently completed its ambitious observing campaign comprising 840 orbits and 1000 hours of the Hubble and Spitzer Space Telescopes, respectively. Imaging six deep fields around massive lensing clusters, the FF program will reveal the population of galaxies at redshifts 5--10 that are 10–-50 times fainter intrinsically than any presently known and it will help to solidify our understanding of the structures, stellar masses and star formation histories of faint galaxies across most of the age of the universe, down to, and including, the redshifts of the targeted galaxy clusters. I will highlight a number of recent discoveries made from the FF images and associated spectroscopic followup observations, including galaxy candidates discovered at z>8, gravitationally lensed dusty star-forming galaxies detected at far-infrared wavelengths with ALMA and the LMT, and the remarkable multiply-imaged supernova "Refsdal", a Type-II explosion at z=1.49 that has provided a unique and valuable tool for testing lensing and cluster dark matter models.


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Previous Years' Abstracts