Department of Astronomy & Physics

Colloquia & Current Events 2017 - 2018

Colloquia Abstracts
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Archived Colloquia 2016-17

Archived Colloquia 2015-16

Archived Colloquia 2014-15

Archived Colloquia 2013-14

Probing the galaxy-mass connection in TeraByte-scale imaging surveys

Speaker: Dr. Jean Coupon (University of Geneva)
Time: November 24, 2017 - 3:00 PM
Location: Atrium 101


The past decade has seen the emergence of new techniques and exciting discoveries powered by wide-field imaging surveys from the UV to the near-IR domain. Owing to gravitational lensing, galaxy clustering and abundance matching (to name but a few), coupled with advanced statistical interpretation, the informative power of astronomical imaging surveys has significantly increased. In particular, the connection between galaxies and dark matter, a keystone in cosmology and the study of galaxy evolution, has widely gained from this "scale revolution" and the future is bright, as the next experiments such as HSC, LSST, Euclid or WFIRST are dedicated "survey" machines that will further increase imaging data by orders of magnitude (without mentioning the tremendous gain in image resolution, time domain and deep near-IR imaging). I will focus my talk on reviewing the main techniques to connect galaxies and dark matter in the context of wide-field surveys and I will show some concrete examples of applied data analysis in the CFHTLenS and COSMOS projects, showing that these techniques are now well proven, although the challenges in reducing some critical systematic uncertainties are ahead of us.


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Electron capture on Ne-20 and the ultimate fate of medium-mass stars

Speaker: Dr. Oliver Kirsebom (Aarhus University)
Time: January 12, 2018 - 3:00 PM
Location: Atrium 101


Medium-mass stars develop an electron-degenerate core consisting mainly of oxygen and neon, which can become so heavy that it collapses under its own weight. While such a collapse is all but certain to trigger a thermonuclear runaway, the impact on the star is highly uncertain and depends critically on the density at which oxygen ignites, with lower densities favouring disruption of the stellar core and higher densities favouring collapse into a neutron star.
Understanding the final evolution of medium-mass stars is an interesting problem in itself, but it is also necessary if we want to understand how these stars contribute to galactic chemical evolution.
In my talk, I will review what we known about the final evolution of medium-mass stars, explain why electron-capture reactions on Ne-20 nuclei are important in this connection, and discuss ongoing efforts to improve our understanding of these reactions in laboratory experiments.


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Eclipse Chasing in Nebraska

Speaker: Dave Lane (SMU) and Dave Chapman
Time: September 15, 2017 - 3:00 PM
Location: Atrium 101


Several Nova Scotians and many other Canadians headed to Nebraska (and other western states) last month to view the Great American Total Solar Eclipse. This "light" colloquium will chronicle our journey, experiences and some of the images and video collected by us and other Canadians.



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Eta Carinae: a Rosetta Stone or an anomaly?

Speaker: Dr.  Ted Gull   (NASA/GSFC)
Time: September 22, 2017 - 3:00 PM
Location: Atrium 101


The first metals that enriched the interstellar medium came from very massive stars that evolved quickly. We can gain understanding of the physical processes by studying nearby massive stars in the present epoch, especially those that have undergone rapid evolutionary changes leading to huge ejections. However their estimated frequency is about one per galaxy per century.

Fortunately the massive star with historical ejection in our Milky Way, Eta Carina, is sufficiently nearby that we are able to study the ejected material and even monitor its current behavior with modern observatories. 

I will describe observations and models of the Eta Carina binary system, its fossil wind structures and its nineteenth century ejecta: the Homunculus and the Little Homunculus. 3D models of the Homunculus and the current interacting winds will be presented. Questions still persist on how Eta Carina might explain the distant supernova imposters, some of which precede actual supernovae.


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What drives the growth of supermassive black holes? -- Galaxy interactions versus secular evolution

Speaker: Dr. Andy Goulding (Princeton)
Time: September 29, 2017 - 3:00 PM
Location: Atrium 101


Collisions and interactions between galaxies are thought to be pivotal stages in their formation and evolution, causing the rapid production of new stars, and possibly serving as a mechanism for fueling the most rapid growth of supermassive black holes (BH). However, the majority of more moderate luminosity growing BHs, so called active galactic nuclei, appear to be hosted in isolated disk-like systems. These spiral galaxies do not appear to have undergone a significant merger in the last 2-3 billion years, and are evolving along a more secular route.
I will discuss our recent efforts to harness the enormous statistical power of wide-field surveys, such as the Hyper Suprime Camera Survey and the Sloan Digital Sky Survey, to perform a multi-wavelength analysis of BHs and their galaxies, and to investigate AGN triggering in the context of galaxy evolution.


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MacLennan Memorial Lecture in Astronomy (public lecture) presents: Exoplanets and the Search for Habitable Worlds

Speaker: Dr. Sara Seager (MIT)
Time: October 20, 2017 - 7:00 PM
Location: McNally Theatre Auditorium


Thousands of exoplanets are known to orbit nearby stars with compelling evidence that all stars in our Milky Way Galaxy likely have planets. Beyond their discovery, a new era of “exoplanet characterization” is underway with an astonishing diversity of exoplanets driving the fields of planetary science and engineering to new frontiers. The push to find smaller and smaller planets down to Earth size is succeeding and motivating the next generation of space telescopes to have the capability to find and identify habitable worlds. The ultimate goal is to discover planets that may have suitable conditions for life or even signs of life by way of atmospheric biosignature gases.


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Dark Matter Substructure: Cosmological Treasure Trove or a Pandora's Box

Speaker: Dr. Frank van den Bosch (Yale)
Time: October 27, 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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Stellar activity in exoplanet observations

Speaker: Dr. Giovanni Bruno (STScI)
Time: November 3, 2017 - 3:00 PM
Location: Atrium 101


While being a treasure of information for stellar physicists, stellar activity is a major source of headaches for exoplaneteers. Transit photometry and radial velocities, the main techniques to measure the radius and mass of exoplanets, are affected by the noise and systematic errors introduced by phenomena related to stellar activity, such as starspots. This is a serious limitation because the mass and radius of a planet are necessary parameters to model its internal structure. Starspots also affect the atmospheric characterization of exoplanets, as they can mimic particular spectral features which can erroneously be interpreted as aerosol signatures in otherwise clear atmospheres.

I will review the main challenges due to stellar activity and present different ways it can be dealt with, with their advantages and disadvantages, discussing real cases. We are far from the solution to this problem, but recent improvements in survey precision, analytic modeling and computational techniques give some reasons to be optimistic.


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