| September 30, 2020 |
Speaker: Di Li |
Title: The Commensal Radio Astronomy FAST Survey (CRAFTS) |
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Institute: Chinese Academy of Science |
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Host: Vikram Ravi |
Abstract: The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has released its first call for proposal and will be open to the international community next year. Based on a novel technique of high-cadence CAL injection, we have realized the world's first calibrated commensal survey mode, simultaneously taking data for pulsar search, HI galaxies, HI imaging, and FRBs. I introduce here one of the major survey plans, namely, the Commensal Radio Astronomy FAST Survey (CRAFTS, Li et al. 2018), which has discovered more than 100 new pulsars, including a few dozen MSPs, 5 new FRBs, including one new repeater. I will also briefly describe recent FAST results from CRAFTS and other dedicated programs, including new insights into the characteristic energy of FRBs, the formation process of neutron stars, the evolution of interstellar medium, etc. |
| October, 2, 2020 |
Speaker: Danielle Berg |
Title: Extreme UV Emission: Bridging Galaxy Evolution Across Cosmic Time |
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Institute: OSU / UT Austin |
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Host: Chuck Steidel |
Abstract:In the last few years, our first glimpse of the spectral properties of z∼5−7 galaxies has emerged. Deep UV spectra have revealed prominent high-ionization nebular emission lines (i.e., C IV, He II, C III]) indicating that extreme radiation fields may be characteristic of reionization-era systems. While such strong high-ionization emission lines are atypical of the well-studied z∼0−3 galaxy samples, our recent UV spectral campaigns have revealed several galaxies with analogous emission-line features to reionization-era systems. I will discuss the recent detection of extremely strong UV emission in nearby galaxies and the potential sources of their very hard ionizing radiation fields. Such strong detections of high-ionization emission lines have been linked to the leakage of Lyman continuum (LyC) photons (necessary for reionization) both theoretically and observationally. These extreme UV emission-line dwarf galaxies provide a template for the extreme conditions that are important for reionization, however their features are still poorly understood. In preparation for the coming UV window onto the early universe with the advent of ELTs and JWST, I will introduce the COS Legacy Archival Spectroscopic SurveY - an upcoming large HST program designed to disentangle the stellar and nebular spectral signatures of 45 star-forming galaxies. This program will calibrate new UV diagnostics that will allow us to trace galaxy evolution to the distant universe, unveiling the properties of reionization-era galaxies. |
| October 14, 2020 |
Speaker: Keith Hawkins |
Title: Galactic Archaeology with Gaia and Large Spectroscopic Surveys |
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Institute: UT Austin |
One of the key objectives of modern astrophysics is to understand the formation and evolution galaxies. In this regard, the Milky Way is a critical testing ground for our theories of galaxy formation. However, dissecting the assembly history of the Galaxy, requires a detailed mapping of the structural, dynamical chemical, and age distributions of its stellar populations. Recently, we have entered an era of large spectroscopic and astrometric surveys, which has begun to pave the way for the exciting advancements in this field. Combining data from the many multi-object spectroscopic surveys, which are already underway, and the rich dataset from Gaia will undoubtedly be the way forward in order to disentangle the full chemo-dynamical history of our Galaxy. In this talk, I will discuss my current work in Galactic archaeology and how large spectroscopic surveys have and can been used to dissect the structure of our Galaxy. I will also explore the future of Galactic archaeology through chemical cartography. |
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Host: Jim Fuller |
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| October 21, 2020 |
Speaker: Ben Oppenheimer |
Title: Why Measuring Black Hole Masses is Essential for Understanding the Circumgalactic Medium |
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Institute: University of Colorado |
Abstract: Ripped straight from the headlines of the award of this year's Nobel Prize in Physics, I will begin by discussing the potential connection between a galaxy's central supermassive black hole (SMBH) and its gaseous halo, the circumgalactic medium. Cosmological simulations predict a direct connection between these dramatically different scales, which causally arises from the integrated history of SMBH feedback expelling gas beyond the virial radius. While observing this connection is currently challenging, I will discuss the potential of observing hot gaseous halos in X-rays around Milky Way-mass galaxies. I plan to continue discussing Milky Way-mass halos as observed through via UV absorption line signatures, including changes with redshift from z=3 to today. |
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Host: Chuck Steidel |
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| October 28, 2020 |
Speaker: Gwen Rudie |
Title: Feedback and Feeding: The Circumgalactic Medium of Star-Forming Galaxies during Cosmic Noon |
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Institute: Carnegie Observatories |
The exchange of baryons between galaxies and their surrounding intergalactic medium (IGM) is a crucial but poorly constrained aspect of galaxy formation and evolution. I will present three surveys that use classical IGM absorption line techniques to better understand gas flows and the impact of environment on the life cycle of galaxies. Most of my talk will focus on a new detailed study of metal-enriched absorbing gas in the high-z (2"<"z"<"3) circumgalactic medium (CGM) using data from the Keck Baryonic Structure Survey (KBSS). I will highlight results on the size, kinematics, and thermal properties of circumgalactic gas which provide clear evidence of unbound metal-enriched gas within the halos of "z~2" galaxies and demonstrate the CGM at cosmic noon requires constant heating or replenishment of warm gas. Collectively, these data suggest the CGM provides one of the best testing grounds for models of galaxy-scale outflows. Next, I will briefly show forthcoming results from the Cosmic Ultraviolet Baryon Survey (CUBS) which aims to understand the turn down in the cosmic star formation rate density through study of the CGM at 0.4 "<" z "<" 1.0 using HST/COS. I’ll conclude with a short discussion of a new survey underway at Magellan to map the large-scale environment of galaxies at cosmic noon, the Lyman-alpha Tomography IMACS Survey (LATIS). Collectively, these surveys constrain the nature and sphere of influence of galaxy-scale outflows and intergalactic accretion, as well as the impact of environment on galaxies at cosmic noon and beyond. |
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Host: Chuck Steidel |
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| November 4, 2020 |
Speaker: Natasha Batalha |
Title: Interpreting Exoplanet Atmospheres at the Onset of Next-Generation Telescopes |
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Institute: NASA Ames |
Abstract: One of NASA's primary goals is to observationally characterize exoplanet atmospheres, understand the chemical and physical processes of exoplanets and improve the understanding of the origins of exoplanetary systems. Throughout the next decade and beyond, JWST, WFIRST, future mission concepts, and ground based telescopes will work towards achieving these goals by interpreting a diverse set of exoplanet atmosphere observations, ranging from hot gas giants to small temperate rocky worlds. Our understanding and interpretation of this full gamut of spectroscopy data will hinge on our ability to accurately link observations to theoretical models. Therefore, it is imperative that our theoretical models are equipped to tackle these problems. Leading up to this new era in exoplanetary space science, one of our goals has been to ensure that the community is equipped with robust, user-friendly, open-source, theoretical models needed to both plan and execute ground-breaking science. I will first discuss the current landscape of theoretical exoplanet model development. Then, I will discuss our recent developments in cloud, opacity, and spectroscopy models that will work together to enable effective interpretation of exoplanet spectroscopy during this next-generation of observations. |
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Host: Tiffany Meshkat |
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| November 11, 2020 |
Speaker: Subo Dong |
Title: Direct Collision of White Dwarfs as a Possible Major Channel for Type Ia Supernovae |
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Institute: Peking University |
Abstract: The explosion mechanism of Type Ia supernovae (SN Ia) is unknown. The continuity in the properties of SNe Ia across the luminosity function suggests a single dominant channel to explain the population. We argue that direct collisions of white dwarfs may be promising as such a major channel. I will present results of our efforts to test the collision model. |
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Host: Ilaria Caiasso |
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| November 18, 2020 |
Speaker: Joss Bland-Hawthorn |
Title: Galactic seismology: the evolution of the “phase spiral” after the Sagittarius impact |
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Institute: University of Sydney |
Abstract: Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be studied using the full distribution of stars, from white dwarfs to supergiants. The oldest components provide unique insight into how galaxies form and evolve over billions of years. This is a veritable golden age for galactic archaeology with many large surveys now under way to map both chemistry and motions for stars in the Galaxy. Detailed 6D "phase space" information combined with chemistry for millions of stars heralds a new era in how we slice up the Galactic disc. This has already enabled the most remarkable discovery to emerge from ESA's Gaia satellite — the “phase spiral”. This phenomenon, which was not foreseen, is direct evidence of giant waves crossing the disc. We discuss how the phase spiral is generated and what it may tell us about our history. We review the main science goals of Galactic seismology, and look to what the future may hold. These studies will continue to play a fundamental role far into the future because there are measurements that can only be made in the near field and contemporary astrophysics depends on such observations. |
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Host: Chris Martin |
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| December 2, 2020 |
Speaker: Ann-Marie Madigan |
Title: Collective Gravity in the Outer Solar System |
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Institute: University of Colorado |
Abstract: There’s something odd going on in our solar system. While the planets move on nearly-circular orbits in a well-defined plane, the minor planets beyond Neptune appear to cluster together in a highly-inclined, eccentric, and tilted structure. Astronomers have invoked the presence of an additional planet (Planet 9) or even a primordial black hole in explanation. In this talk I will show that these theories may be unnecessary. In analogy with spiral arms and bars in galaxies, the collective gravity of individually small but collectively massive bodies can create such structures in the outer solar system. |
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Host: Tiffany Meshkat |
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| December 9, 2020 |
Speaker: Rebecca Jensen-Clem |
Title: Exoplanet Imaging with Extremely Large Telescopes |
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Institute: UCSC |
Abstract: In the last thirty years, over 3000 planets have been discovered orbiting nearby stars. This flood of new worlds includes planets unlike any found in our own Solar System, from Jupiter-mass planets with years as short as our day to exotic rocky worlds twice as massive as the Earth. While our understanding of exoplanets' diversity has leapt forward in recent years, fundamental questions remain. For example, what are the dominant planet formation pathways? How do planets acquire their atmospheres? Is there life on other worlds? These questions can only be answered through observations of exoplanets’ spectra, where the characteristic imprints of atoms and molecules making up a planet’s atmosphere are revealed. The most promising method for obtaining spectra of diverse exoplanets is direct imaging: by nulling the light of the parent star with an optical device called a coronagraph, the planet itself can be seen and its light dispersed into a spectrum. So far, only extremely young, massive worlds have been directly imaged, while older, lower mass objects like the Earth remain hidden in the glare of their host stars. In this talk, I will describe two avenues for advancing the state-of-the-art in exoplanet imaging: 1) detecting low-mass exoplanets at Solar System separations with the W. M. Keck Observatory and Thirty Meter Telescope via predictive wavefront control and focal plane wavefront sensing, and 2) characterizing the atmospheres of directly imaged planets with polarimetry -- an untapped method for probing the physics of clouds in the atmospheres of other worlds. |
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Host: Mansi Kasliwal |
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| January 6, 2021 |
Speaker: Ellen Zweibel |
Title: Cosmic Rays in Multiphase Gas |
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Institute: University of Wisconsin-Madison |
Abstract: Cosmic rays appear to be universal in galaxies with star formation or nuclear activity. They play a role in the dynamics, energy balance, and stability of the diffuse gas in these systems, and are now included in many state of the art models of galaxy formation and evolution. The exchange of energy and momentum between cosmic rays and thermal gas is largely collisionless, mediated by kinetic scale plasma waves. The properties of these waves depend both on local conditions and the global structure of the thermal gas, introducing complex feedback loops that are only beginning to be probed theoretically and incorporated into models. I will discuss some recent progress in this area, focusing on the role of interstellar clouds. |
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Host: Jim Fuller |
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| January 20, 2021 |
Speaker: Stephen Smartt |
Title: Mergers, magnetars and multi-messengers |
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Institute: Queens University Belfast |
Abstract: |
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Host: Mansi Kasliwal |
Wide-field optical sky surveys are discovering a remarkable diversity |
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PLEASE NOTE: THIS TALK WILL BE HELD |
in how stars merge, collapse and explode. A number of unusual and |
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AT 12:00 PM (NOON) instead of 4:00pm |
fast declining transients have been found, but their true volumetric rate |
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appears low. The powering mechanism for |
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many of these requires a source beyond radioactivity, plausibly a |
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magnetic, rapidly spinning neutron star. In addition, the discovery of |
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an electromagnetic counterpart to a pair of merging neutron stars |
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showed that gravitational wave sources produce transients that emit photons |
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from gamma rays to the radio. Spectral analysis provides a method to |
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determine the composition, ejecta velocity and kinetic energy of the transients, |
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which helps constrain their nature. I will highlight our recent searches for degenerate |
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mergers and fast transients with ATLAS and Pan-STARRS. I will also show |
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how spectroscopic analysis can uncover the composition of these unusual |
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objects. |
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| January 27, 2021 |
Speaker: Erin Kara |
Title: Reverberation mapping black hole accretion flows |
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Institute: MIT |
Sitting at the heart of nearly all galaxies is a massive black hole, that, while typically 1000 times less massive than the galaxy in which it resides, has the potential to release enough energy via accretion of gas onto the black hole, to completely unbind the entire galaxy. Most of the power from an Active Galactic Nucleus (AGN) is released close to the black hole, and thus studying the inner accretion flow, at the intersection of gas inflow and energy outflow, is essential for understanding how black holes grow and affect galactic evolution. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and the black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and show how extending these X-ray spectral-timing techniques to transient accretion episodes is helping us probe the formation of X-ray coronae, jets and other relativistic outflows. |
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Host: Ilaria Caiazzo |
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| February 3, 2021 |
Speaker: Francois Combes |
Title: |
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Institute: Observatoire de Paris |
Abstract: |
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Host: Chris Martin |
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| February 10, 2021 |
Speaker: Silvia Toonen |
Title: |
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Institute: University of Birmingham |
Abstract: |
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Host: Jim Fuller |
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| February 17, 2021 |
Speaker: Tim Bedding |
Title: |
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Institute: University of Sydney |
Abstract: |
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Host: Jim Fuller |
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| March 10, 2021 |
Speaker: Risa Wechsler (Biard Lecture) |
Title: |
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Institute: Stanford University |
Abstract: |
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Host: Mansi Kasliwal |
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