DAO Astronomy Colloquium

DAO Astronomy Colloquium Schedule

Online via Zoom, Victoria

Tuesdays at 11am unless otherwise indicated with (***)

Archive of previous seminar schedules (2010-)
Link to remote connection information


Spring/Summer 2021

Tues March 23rd, 11am,  Zoom: Meredith Macgregor (U. of Colorado Boulder) Recording

How to Form a Habitable Planet: More than 20% of nearby main sequence stars are surrounded by debris disks, where planetesimals, larger bodies similar to asteroids and comets in our own Solar System, are ground down through collisions.  The resulting dusty material is directly linked to any planets in the system, providing an important probe of the processes of planet formation and subsequent dynamical evolution.  The Atacama Large Millimeter/submillimeter Array (ALMA) has revolutionized our ability to study planet formation, allowing us to see planets forming in disks and sculpting the surrounding material in high resolution.  I will present highlights from ongoing work using ALMA and other facilities that explores how planetary systems form and evolve by (1) connecting debris disk structure to sculpting planets and (2) understanding the impact of stellar flares on planetary habitability.  Together these results provide an exciting foundation to investigate the evolution of planetary systems through multi-wavelength observations. 

Tues March 30th, 11am, Zoom: Hanno Rein (U. of T) Recording

Chaos, Instability, and Machine Learning: We have known the equations which determine the trajectories of planets for over 300 years. Yet, the long term evolution of the Solar System was not well understood until just a few years ago. In this talk, I will explain why it is so hard to solve these differential equations and describe the recent algorithmic breakthroughs that have made such problems tractable. These new numerical tools allow us to address many exciting scientific questions. I will outline some of my current research projects which aim to improve our understanding of planet formation in our galactic neighbourhood, and put constraints on General Relativity on timescales of billions of years. I will also present how we construct a Bayesian neural network to accurately predict instabilities orders of magnitudes faster than was possible before. This model enables us to include stability constraints in data reduction pipelines for extrasolar planetary systems.

Tues April 6th, 11am, Zoom: Tuan Do (UCLA) Recording Unavailable

The Galactic Center: a laboratory for the study of the physics and astrophysics of supermassive black holes: The center of the Milky Way hosts the closest supermassive black hole and nuclear star cluster to the Earth, offering us the opportunity to study the physics of supermassive black holes and their environment at a level of detail not possible elsewhere. I will discuss 2 major questions that are at the forefront of Galactic center research: (1) What is the nature of the near-infrared emission from Sgr A*? and (2) How do nuclear star clusters form and evolve in the vicinity of a supermassive black hole? I will show how the long time-baseline of Galactic center observations, improved instrumental capabilities, and use of statistical methods to combine many types of data have led us to new insights into these questions. I will discuss what we have learned in 20 years of observations of the supermassive black hole, Sgr A*, in the near-infrared and its surprising increase in activity in recent years. I will also discuss how the results the first chemical-dynamical model of the Milky Way Nuclear Star Cluster allow us to disentangle its complex formation.

Tues April 13th, 11am, Zoom: Deep Anand (U. of Hawaii) Recording

Cosmicflows-4: Tip of the Red Giant Branch Distances: The tip of the red giant branch (TRGB) is becoming the preferred technique to determine accurate distances to galaxies within the local Universe. The method involves using the brightest red giant branch stars as standard candles, and has now been applied to nearly 500 galaxies within 20 Mpc. Accurate distances are essential for transforming observed properties of galaxies into their physical counterparts (luminosity, physical size, etc.). In addition to their inherent benefits, distances allow us to disentangle the two components of a galaxy’s observed velocity, the component due to the Hubble Flow, and its peculiar velocity. With the latter, we map the patterns of large-scale galaxy flows, and provide insight into the formation and evolution of large-scale structure. In this talk, I will present an update on the TRGB component of the Cosmicflows-4 program, and showcase several recent results from this work, including a discussion on the implications for the value of the Hubble Constant.

Tues April 20th, 11am, Zoom: Auriane Egal (Western U.) Recording

Comet Halley’s twin meteor showers: 1P/Halley is a famous comet that aroused the interest of the general public and the scientific community for several centuries. Its most recent apparition in 1986 motivated an unprecedented observational effort, combining spacecraft rendezvous and ground-based telescopic programs led by different countries. Most of our knowledge about the comet’s activity and evolution comes from the results of this exceptional observation campaign. From the analysis of ancient Chinese and Babylonian inscriptions, we suspect that 1P/Halley has been delivering meteoroids to Earth for several millennia. In particular, the comet is known to produce two meteor showers at the present epoch, the Eta-Aquariids in May and the Orionids in October. However, and despite decades of meteor observations, most of the showers’ characteristics are still unexplained. In this presentation, we expose the results of a new numerical model of 1P/Halley’s meteoroid streams, allowing to reproduce the meteor showers’ formation, intensity, duration, and predict the apparition of future meteor outbursts to watch. In particular, we expect three Eta-Aquariids outbursts in the future that deserves special attention.

Tues April 27th, 11am, ZoomOliver Müller (U. of Strasbourg) Recording

A cosmic ballet of dwarf galaxies as challenge for dark matter cosmology: Dwarf galaxies are not only the most common galaxies but also the most dark matter dominated objects in the universe. By studying their abundance and distribution, we can test our current model of cosmology. Around the Milky Way and the Andromeda – the Local Group –, several discrepancies between observations and the predictions for these dwarf galaxies have been identified, constituting a small-scale crisis. The most severe of them is the plane-of-satellites problem: the dwarf galaxy satellites around the Milky Way and the Andromeda are aligned in thin, planar, co-rotating structures. This is in stark contrast to the results of cosmological simulations, where for the satellite system an isotropic distribution with random motions is expected. This raises the question: Is the Local Group unique? Recent observations of the nearby Centaurus group say it is not. In my talk, I will give a review over the current state of this peculiar question in near-field cosmology.

Tues May 4th, 11am, Zoom: Judit Prat (DES/U. of Chicago) Recording

Galaxy-galaxy lensing and Lensing Ratios for Cosmological Analyses in the Dark Energy Survey: Galaxy cosmic surveys such as the Dark Energy Survey are a powerful tool to extract cosmological information. In particular, the combination of weak lensing and galaxy clustering measurements, usually known as 3x2pt, provides a potent and robust way to constrain the parameters controlling the structure formation in the late Universe. Galaxy-galaxy lensing, which is the cross-correlation of the shapes of source background galaxies with lens foreground galaxy positions, is one of the three probes that is part of this combination. In this talk, I will describe how we can accurately measure and model galaxy-galaxy lensing correlations using the well-understood large scales with the purpose of extracting cosmological information. Besides this, I will also describe how we can construct suitable ratios of these measurements to exploit the otherwise usually disregarded small-scale information and naturally integrate it as a part of the 3x2pt analysis.

Tues May 25th, 11am, Zoom: Carl Fields (MSU/Arizona/LANL)  Recording

Next-Generation Simulations of The Remarkable Deaths of Massive Stars: Core-collapse supernova explosions (CCSN) are one possible fate of a massive star. Simulations of CCSNe rely on the properties of the massive star at core-collapse. As such, a critical component is the realization of realistic initial conditions. Multidimensional progenitor models can enable us to capture the chaotic nuclear shell burning occurring deep within the stellar interior. I will discuss ongoing efforts to progress our understanding of the nature of massive stars through next-generation hydrodynamic stellar models. In particular, I will present recent results of three-dimensional hydrodynamic massive star models evolved for the final 10 minutes before collapse. These recent results suggest that realistic 3D progenitor models can be favorable for obtaining robust models of CCSN explosions and are an important aspect of massive star explosions that must be taken into consideration. I will conclude with a brief discussion of the implications our models have for predictions of multi-messenger signals from CCSNe.

Tues June 1st, 11am, Zoom: Yamila Miguel (Leiden) Recording

Unveiling the secrets of Jupiter with the Juno mission: With more than 4000 exoplanets found and about 2-dozens of planets with detected atmospheric chemical species, we moved from an era of discovery to a new era of exoplanet characterisation. On the other hand, extremely accurate measurements by Juno and Cassini missions, make this an exceptional time to combine the detail information on the solar system giant planets and the large amount of data from exoplanets to get a better understanding on planetary physics and a better comprehension on planet formation and evolution. Because our knowledge on the interior structure of the giant planets is linked with the data we obtain from space missions, these last years were crucial for this field: the outstanding accuracy of the gravity data provided by Juno has fundamentally changed our understanding of the interior of Jupiter. It has allowed us to put constrains on the zonal flows, the extent of differential rotation and lead us to find that Jupiter has most likely a dilute core. In this presentation I will review our knowledge on the interior structure of Jupiter and will also show some new results where we find that a non-homogenous envelope is also a constraint set up by the Juno measurements, which is helping us to get closer to unveiling Jupiter’s deep secrets and to reach a better understanding of the giant planets formation history.

Tues June 8th, 11am, Zoom: Shany Danieli (IAS) Recording

Towards a better understanding of low mass galaxies beyond the Local Group: Low mass galaxies provide an essential testing ground for theoretical predictions of cosmology. Their number densities, structures, and internal dynamics can be extremely insightful for studying dark matter and galaxy formation on small scales. I will discuss recent results studying dwarf galaxies and ultra-diffuse galaxies (UDGs). UDGs hold the promise of new constraints on low mass galaxies dynamics, as their spatial extent and often significant globular cluster populations provide probes on spatial scales where dark matter should dominate the kinematics. I will also discuss the dynamics of two UDGs that seem to lack most, if not all, of their dark matter and host an intriguing population of globular clusters. I will finish by presenting a new wide-field survey carried out with the 48-lens Dragonfly Telephoto Array. With an excellent photometric depth, the Dragonfly Wide Field Survey will provide an unprecedented view of the low surface brightness universe over a wide area of the sky (350 square degrees). The main goal of the survey is to provide information on the properties and statistics of the dwarf galaxy population beyond the Local Group but it will also provide a useful resource for other resolved, low surface brightness phenomena, such as stellar streams and tidal tails, stellar halos, intragroup light and the extent of massive galaxies.

Tues June 22nd, 11am, Zoom: Jane Huang (U. of Michigan) Recording

The ALMA View of Planet Formation: The ubiquity and diversity of planets tell us that they can emerge under an astonishing range of conditions. By enabling us to map the distributions of dust grains and molecules in protoplanetary disks at an unprecedented level of detail, the Atacama Large Millimeter/Submillimeter Array (ALMA) has transformed our understanding of planet formation. In the Disk Substructures at High Angular Resolution Project (DSHARP), we undertook the first high angular resolution disk survey at millimeter wavelengths. Although protoplanets are difficult to detect directly, the widespread presence of dust gaps and rings in disks suggests that giant planet formation may occur readily on Myr-timescales at surprisingly wide separations. Meanwhile, in a small but growing number of systems, detections of puzzling spiral structures oblige us to re-examine common assumptions about the reservoir of material available for planet formation. ALMA has also revealed strong chemical heterogeneity within and among disks, laying the observational groundwork for linking the compositions of planets to their formation location. Together, these new data show that the natal environments of planets are far more dynamic and varied than earlier observations have indicated.