March 28, 2018 | 3:30 PM | ERC 401 | Wednesday colloquium Gauge-field inflation and the origin of the matter-antimatter asymmetry Peter Adshead, University of Illinois at Urbana-Champaign
The basic inflationary paradigm is in good shape. On the one hand, the observed density fluctuations are adiabatic, gaussian and are red-tilted---characteristics in general agreement with simple models built from scalar fields. On the other hand, B-mode polarization of the cosmic microwave background sourced by primordial gravitational waves, the so-called smoking-gun signature of inflation, remains elusive. Upcoming and planned experiments will make increasingly precise B-mode measurements, potentially putting the inflationary paradigm through a stringent test.
In this talk, I describe a new class of inflationary scenarios which utilize gauge fields to generate inflationary dynamics in the early universe. Beyond simply providing yet another model for inflation, these scenarios furnish unique observational imprints which distinguish them from standard scalar-field scenarios. In particular, these scenarios generically result in large-amplitude, chiral gravitational waves and provide counterexamples to the standard claim that an observable tensor-to-scalar ratio requires inflation at the grand unification scale, as well as super-Planckian excursions of the inflaton. In addition I discuss how these chiral gravitational waves may be responsible for the matter-antimatter asymmetry of the Universe.
April 4, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Science, Politicians, and the Public: What's the Story? Rush D Holt, AAAS
Video With many public decisions being made on the basis of political partisanship rather than scientific evidence, what storyline should scientists follow and what difference does it make for the practicing researcher?
April 11, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Preliminary Cosmology Results from the Dark Energy Survey Supernova Program Rick Kessler, The University of Chicago
Video We have recently completed 5 seasons of the Dark Energy Survey (DES), and cosmology results starting coming out last summer. Here I will discuss new cosmology results based on a subset of spectroscopically confirmed SNIa, and describe advances in the analysis aimed for much larger samples in DES and beyond. Finally, I will briefly describe other science projects using the DES transient-search pipeline.
April 18, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Pushing the Boundaries: Expanding Possibilities for Exoplanet Atmospheric Characterization Emily Rauscher, University of Michigan
With the launch of NASA's Transiting Exoplanet Survey Satellite, the (eventual) launch of the James Webb Space Telescope, and the continual development of ground-based capabilities and construction of extremely large telescopes, we have an expanding ability to collect atmospheric data on many more exoplanets, and much more highly detailed data on the brightest ones. The biggest, brightest transiting planets will always be hot Jupiters which, although we have been observing and modeling their atmospheres for over a decade, remain far from a "solved problem". I will discuss two types of observational techniques that can provide new, highly detailed information about their atmospheres: high-resolution spectroscopy, which provides direct measurement of a planet's rotation rate and wind speeds, and eclipse mapping, which resolves a two-dimensional image of the planet's day side. Each of these methods will enable us to tackle outstanding scientific questions. Then, as we are increasingly able to perform atmospheric characterization measurements of more diverse types of exoplanets, we will be better able to understand atmospheric and planetary properties writ large. I will provide the example of what new things we will learn from studying "warm Jupiters", just slightly out beyond the standard hot Jupiter population.
April 25, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Strong Lensing: Lenses and Sources Michael Gladders, University of Chicago
I will discuss recent studies of both strongly lensed sources, and the foreground lens population (primarily groups and cluster of galaxies), framed by an overview of where I think the strong lensing research is headed in the next decade. The lensed sources I will detail are primarily selected from the SDSS. Highlights will include the smallest star-forming features ever resolved in a distant galaxy, the new MEGaSaURA atlas of moderate resolution rest-UV spectra of more than a dozen bright lensed galaxies at 1.7<z<3.6, and recent HST observations of Lyman continuum photons from a distant galaxy. I will also detail an extensive program to test whether the observed strong lensing by massive clusters - particularly that from the South Pole Telescope cluster sample - is consistent with theoretical expectations.
May 2, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium The Multi-Messenger Picture of a Neutron Star Merger Brian Metzger, Columbia University
On August 17 the LIGO/Virgo gravitational wave observatories detected the first binary neutron star merger event (GW170817), a discovery followed by the most ambitious electromagnetic (EM) follow-up campaign ever conducted. Within 2 seconds of the merger, a weak burst of gamma-rays was discovered by the Fermi and INTEGRAL satellites. Within 11 hours, a bright but rapidly-fading thermal optical counterpart was discovered in the galaxy NGC 4993 at a distance of only 130 Million light years. The properties of the optical transient match remarkably well predictions for "kilonova" emission powered by the radioactive decay of heavy nuclei synthesized in the expanding merger ejecta by rapid neutron capture nucleosynthesis (r-process). The rapid spectral evolution of the kilonova emission to near-infrared wavelengths demonstrates that a portion of the ejecta contains heavy lanthanide nuclei. Two weeks after the merger, rising non-thermal X-ray and radio emission were detected from the position of the optical transient, consistent with delayed synchrotron afterglow radiation from an initially off-axis relativistic jet (or a shock-heated "cocoon" produced as the jet interacts with the kilonova ejecta). I will describe efforts to create a unified scenario for the range of EM counterparts from GW170817 and their implications for the astrophysical origin of the r-process and the properties of neutron stars (particularly their uncertain radii and maximum mass, which are determined by the equation of state of dense nuclear matter). Time permitting, I will preview the upcoming era of multi-messenger astronomy, once Advanced LIGO/Virgo reach design sensitivity and a neutron star merger is detected every few weeks.
May 9, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium The State of Small-Scale "Crises" In Dark Matter Philip F Hopkins, California Institute of Technology
Video The most fundamental unsolved problems in star and galaxy formation revolve around "feedback" from massive stars (and black holes). I'll review how new generations of theoretical models combine new numerical methods and physics, to try to realistically model the diverse physics of the ISM, star formation, and feedback, on a wide range of scales from those of individual proto-stars to the inter-galactic medium. Feedback produces galactic outflows and perturbs galactic structure in ways which fundamentally perturb the nature of dark matter cores and 'cusps', re-shaping rotation curves and suppressing the central densities of low-mass galaxies. I'll discuss a variety of small-scale "crises" in cold dark matter models: "cusp-core," "missing satellites," "too big to fail," and more, and show that these "crises" tend to simply vanish as higher resolution and more treatments of known physics are included in simulations. However, I will show that there are robust, testable predictions of CDM as compared to other models such as self-interacting or ultra-light scalar field or "warm" dark matter, but these may require fundamentally new observations.
May 16, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium The Remarkable Assembly History of Elliptical Galaxies Richard Ellis, University College, London
Once considered the simplest morphological class with smooth surface brightness profiles and homogenous old stellar populations, elliptical galaxies continue to reveal surprises. I will present the results of several comprehensive spectroscopic campaigns of what are considered to be the precursors of present-day ellipticals seen at redshifts up to and beyond 2. Good signal to noise absorption line spectra are capable of probing the stellar kinematics and stellar populations in early examples providing valuable insight into the assembly history of passive galaxies. I will discuss several puzzles that have emerged from such data including how the compact precursors (or "red nuggets") grew in physical size but hardly in stellar mass, and why early massive examples display rapidly rotating stellar disks in contrast with local examples.
May 23, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Small Galaxies, Big Science: The Booming Industry of Milky Way Satellite Galaxies Alex Drlica-Wagner, Fermilab
The small satellite galaxies of our Milky Way are the most ancient, most metal-poor, and most dark-matter-dominated systems known. These extreme objects offer a unique opportunity to test the standard model of cosmology, while also providing insights into the formation of galaxies, stars, and the heavy elements. Over the past three years, the unprecedented sensitivity of the Dark Energy Camera has allowed us to double the known population of ultra-faint Milky Way satellites. I will discuss recent results, outstanding questions, and upcoming advances in the study of the Milky Way's dark companions.
May 30, 2018 | 3:30 PM | ERC 401 | Astronomy Colloquium Astrophysics Flagships, Present & Future Ken Sembach, STScI
NASA's Great Observatories have revolutionized our understanding of the Universe. The James Webb Space Telescope will continue this legacy, and together with the Hubble Space Telescope and Wide-Field Infrared Telescope will usher in an era of unprecedented information about astronomical objects ranging from Solar System objects to the first stars and galaxies formed near the beginning of time. As we continue to explore, new questions arise. Are there Earth-like planets orbiting other stars, and if so are they capable of supporting life? What secrets does the ultra-faint universe hide from our view? What is the nature of dark matter and dark energy? Future flagship missions offer great promise for answering such questions. In this talk, I'll offer some perspectives, both scientific and programmatic, on possible paths forward and the importance of truly ambitious space observatories to the future of astrophysics research.
June 6, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Physical Manifestations of Evolution, Regularity and Chaos In and Around Our Galaxy Kathryn Johnston, Columbia University
Our Galaxy is thought to be dynamically young with a fairly smooth potential dominated by a nearly spherical dark matter halo that has evolved little in the last several billion years. These attributes broadly suggest that potential evolution and dynamical chaos should have negligible influences on the orbits of its constituent stars, as well as on the stellar structures they collectively support. This talk reviews some recent results which point to signatures of Galactic evolution and the chaotic nature of stellar orbits that can be (and have been) observed.
June 13, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium The X-Ray Emission From Young Supernovae Vikram Dwarkadas, University of Chicago
Detection, identification and analysis of young supernovae (SNe) has generally been the purview of optical astronomy, aided in part by stellar evolution models. But given the fast shocks and high post-shock temperatures, observations at X-ray wavelengths can provide supplementary and very useful information regarding the nature of these objects, their evolution, their abundances, and their progenitors. My students and I have aggregated together data available in the literature, or analysed by us, to compute the lightcurves of almost all young SNe that have been detected in X-rays. Currently we have about 60 SNe spanning all the various types, but the database is expanding rapidly. The lightcurves themselves span 12 orders of magnitude in luminosity. We use this library of lightcurves and spectra to explore the diversity of SNe, the characteristics of the environment into which they are expanding, and the implications for their progenitors. X-ray spectra can provide insight into the density structure, composition and metallicity of the surrounding medium, and the ionization level, through the spectra themselves as well as the X-ray absorption. Since core-collapse SNe expand mainly in environments created by the progenitor star mass-loss, this can provide crucial information about the nature of the progenitor star, and its mass-loss parameters in the decades or centuries before its death. In this talk we will explore the X-ray emission from all types of SNe. Type IIPs have the lowest X-ray luminosities, which sets a limit on the mass-loss rate, and thereby initial mass of a red supergiant star which can become a Type IIP progenitor. Type IIns are observed to have high X-ray luminosities in general, but their light curves are very diverse, with some of them tending to fall off very steeply, and one rising for several thousand days. A recent exciting entry to the category of X-ray SN was the discovery by our group of a Type Ia-CSM, SN 2012ca, the first Type Ia SN of any kind to be detected in X-rays. In this presentation we will investigate what the observations reveal about the medium in which these SNe are expanding, the evolution of the resulting shock waves, and the identity of their progenitors. Our results show that our understanding of how massive stars evolve is highly incomplete, and sometimes incorrect.
June 20, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium A perspective on cosmology from the Antarctic plateau, past, present, and future Thomas Crawford, University of Chicago
The high, dry, cold Antarctic plateau (average elevation ~3000m, average precipitation <3mm/year, winter temperatures <-50C) is the premier site in the world for millimeter-wave astronomy. The most successful cosmological research from the Antarctic plateau so far has been conducted from the NSF Amundsen-Scott South Pole Station. Through the Astronomy Department and later the KICP, Chicago has played a leading role in recognizing the potential of the Antarctic plateau for cosmological observations, developing the infrastructure necessary to make the South Pole a world-class research station, building innovative telescopes and cameras to deploy to the station, and gathering and analyzing data leading to groundbreaking scientific results. I will give my personal perspective on ~20 years of exciting cosmological results from the South Pole and discuss potential future projects exploiting the unique characteristics of the Antarctic plateau, possibly extending beyond the currently developed research stations.
March 30, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Galaxy Cluster Cosmology with the Dark Energy Survey Yuanyuan Zhang, Fermilab
Constraining LambdaCDM cosmology with galaxy cluster abundance is one of the fundamental goals of the Dark Energy Survey (DES). Many thousands of clusters out to redshift 0.65 have been identified in DES data. Weak lensing and multi-wavelength studies with X-ray and cosmic microwave background observations are performed to provide inputs to the cosmology analysis. A cosmology pipeline that considers various systematic effects such as cluster projections and mis-centering is used to derive constraints on LambdaCDM cosmology parameters. In this talk, I will present current progress on DES galaxy cluster cosmology analyses as well as discuss future improvements.
April 6, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Habitability of water-rich exoplanets Nadejda Marounina, University of Chicago
Planets with global water oceans have been the subject of intrigue both in Hollywood and in the exoplanet community. Water worlds are water-rich exoplanets that possess >1% of water by mass, and if located at an appropriate orbital separation from their host star, they may host a global surface water ocean. These habitable (liquid ocean-bearing) water worlds are especially timely because 1) water worlds formed from remnant cores of evaporated mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich habitable zone planets around M dwarf stars, and 2) their larger sizes relative to terrestrial planets make them more amenable to observations with current and upcoming telescopes such as Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). The recent and exciting discovery of TRAPPIST-1 system, that may possess planets with a substantial water/ice fraction, further motivates the study of water-worlds.
In the first part of this talk, I propose to give an overview on the habitability of water-worlds and show you that the the classical estimation of the habitable zone does not apply to this type of exoplanets. In the second part of my talk, I will present the coupled models of planet interiors, clathrate formation, liquid-vapor equilibrium, and atmospheric radiative transfer that are used constrain the atmospheric abundance of CO2 and corresponding habitable zone boundaries of water world exoplanets.
April 13, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Primordial Black Holes in the era of Planck and LIGO Yacine Ali-Haimoud, New York University
LIGO's first direct gravitational-wave detections have revived interest in an old dark-matter candidate, primordial black holes (PBHs). In this talk I will first discuss cosmic microwave background constraints to PBHs in the range of ~10 to a few hundred solar masses. I will then discuss PBH binary formation processes and the resulting merger rates. In particular, I will argue that LIGO may already set the most stringent limits on PBH abundance, provided PBH binaries formed in the early Universe are not strongly perturbed by tidal fields due to non-linear structures.
April 20, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Simulating structure formation in different environments and the applications Chi-Ting Chiang, C.N. Yang Institute for Theoretical Physics/Stony Brook University
The observables of the large-scale structure such as galaxy number density generally depends on the density environment (of a few hundred Mpc). The dependence can traditionally be studied by performing gigantic cosmological N-body simulations and measuring the observables in different density environments. Alternatively, we perform the so-called "separate universe simulations", in which the effect of the environment is absorbed into the change of the cosmological parameters. For example, an overdense region is equivalent to a universe with positive curvature, hence the structure formation changes accordingly compared to the region without overdensity. In this talk, I will introduce the "separate universe mapping", and present how the power spectrum and halo mass function change in different density environments, which are equivalent to the squeezed bispectrum and the halo bias, respectively. I will then discuss the extension of this approach to inclusion of additional fluids such as massive neutrinos. This allows us to probe the novel scale-dependence of halo bias and squeezed bispectrum caused by different evolutions of the background overdensities of cold dark matter and the additional fluid. Finally, I will present one application of the separate universe simulations to predict the squeezed bispectrum formed by small-scale Lyman-alpha forest power spectrum and large-scale lensing convergence, and compare with the measurement from BOSS Lyman-alpha forest and Planck lensing map.
April 27, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Microwave Multiplexing of Superconducting Sensors John A B Mates, University of Colorado, Boulder
Superconducting detectors provide by far the most sensitive measurement of long-wavelength radiation for astronomy and cosmology, with detector noise falling below that of the astronomical signals in the mid-to-late 1990s, depending on the wavelength of interest. To measure better and faster, we have therefore assembled cameras with increasingly large arrays of detectors.
Since the 90s, the size of superconducting detector arrays has followed a Moore's Law trend, which is set to continue into the 100,000 pixel range with instruments like the Simons Observatory and CMB-S4. Perhaps the greatest challenge to continuing this trend is the need to bring the signals from the detector arrays out of a 100 mK cryostat on a much smaller number of wires.
I will present the emerging technique of multiplexing these superconducting sensors using superconducting microresonators. We can use this new scheme with both superconducting Transition-Edge Sensors (TESs) and Microwave Kinetic Inductance Detectors (MKIDs) to read out thousands of highly-sensitive detectors per coaxial cable. This capability will enable new instruments for astronomy and precision cosmology.
May 4, 2018 | 12:00 PM | ERC 401 | Friday noon seminar The early Universe: preparing theory for observations Emanuela Dimastrogiovanni, Case Western Reserve University
I will describe some interesting scenarios for the generation of gravitational waves from inflation and their characteristic imprints, which can be tested with upcoming B-mode observations as well as with interferometers. In the second part of my talk I provide an overview of the physics of CMB spectral distortions and discuss what we can learn from those about the early universe.
May 18, 2018 | 12:00 PM | ERC 401 | Friday noon seminar The Progenitor of the Milky Way's Halo Vasily Belokurov, University of Cambridge/CCA, NYC
We map the composition of the Galactic stellar halo in 7 dimensions spanned by phase-space coordinates and chemical abundances. The local halo appears to be dominated by stars on highly eccentric orbits. These stars are more metal-rich than typically assumed for the Galactic halo and were likely deposited into the Milky Way during an ancient massive accretion event. Using numerical simulations of the stellar halo formation we deduce that this merger must have happened between 8 and 11 Gyrs ago, during the epoch of the Galactic disk formation. This formation scenario for the MW halo has a number of implications for the studies of the evolution of the Galaxy in general and the measurements of the local Dark Matter matter distribution in particular.
May 25, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Beyond the Boost Siavash Yasini, University of Southern California
Our peculiar motion with respect to the cosmic microwave background (CMB) changes the observed frequency and incoming angle of the CMB photons due to the Doppler and aberration effects. The most prominent signature of these motion-induced effects on the CMB is a kinematic dipole, which is observationally indistinguishable from any intrinsic dipole that the CMB might possess. Due to this degeneracy -- and the fact that we theoretically expect the intrinsic dipole of the CMB to be subdominant with respect to the kinematic component -- the 3mK dipole of the CMB is commonly interpreted as an entirely kinematic effect. Consequently, the frame in which the entire dipole of the CMB vanishes is customarily defined as the CMB rest frame. However, if the intrinsic dipole of the CMB is non-zero, this definition would not be appropriate anymore, unless we can properly separate the intrinsic and kinematic components of the dipole. In this talk, I will demonstrate how we can achieve this goal using spectral measurements of the monopole and quadrupole moments of the CMB. I will also describe the impact of the Doppler and aberration effects on the CMB power spectrum (especially on the small angular scales) and their relevance as an observational bias for the current and future surveys. Our recently developed "Generalized Doppler and Aberration Kernel" formalism can be used to measure and remove the motion-induced effects from any arbitrary frequency-dependent cosmological observable.
June 1, 2018 | 12:00 PM | ERC 576 (Note Location Change for this Seminar) | Friday noon seminar Imaging supermassive black holes with the Event Horizon Telescope Lindy Blackburn, Harvard-Smithsonian CfA
The Event Horizon Telescope is an expanding global array of sub-mm radio telescopes designed to directly probe the spacetime geometry and radiative processes on event-horizon scales for the supermassive black holes at the center of our galaxy, Sgr A*, and at the center of M87. A major goal of the EHT is to measure the size and shape of the black hole "shadow," a characteristic signature of strong lensing at the event-horizon and a fundamental prediction of general relativity. In 2017, the EHT operated an 8-station array with both the South Pole Telescope and the ALMA array in Chile for the first time, and included a coordinated campaign of simultaneous ground and space-based multiwavelength observations. While analysis is ongoing, the data achieve an unprecedented 20 micro-arcsecond resolution and provide a direct view of the spatial structure of dynamical processes in the immediate vicinity of Sgr A*.
June 5, 2018 | 2:30 PM | ERC 401 | Special seminar Science News: One year of XENON1T Luca Grandi, KICP
The XENON1T experiment is dark matter direct search that has operated in stable conditions at the Gran Sasso Underground Labs in Italy since December 2016. With an unprecedented target mass and world-record low-background levels for such kind of detectors, XENON1T is the largest liquid xenon time projection chamber operated up to date and it is uniquely placed to explore uncharted territory of the allowed parameter space, further probing the WIMP paradigm, other dark matter models as well as exotic rare-processes. In this science-news talk, I will briefly introduce the project and focus on the recent results from the WIMP search on data collected in the last year of data taking.
June 22, 2018 | 12:00 PM | ERC 401 | Special seminar mm-wave Synoptic Surveys Gilbert Holder, UIUC
Modern high resolution CMB surveys have broad astrophysical applications, ranging from solar system objects to galaxy feedback and reionization. Making dark matter maps, finding strong lenses, and with nearly daily maps of large areas of the variable sky, these surveys have a wide variety of uses.
June 18, 2018 | 2:30 PM | ERC 401 | Open Group seminar Cosmology with curved-sky weak lensing mass maps Marco Gatti, IFAE Barcelona
The statistical analysis of lensed galaxies is a powerful tool to study the dark matter distribution of the Universe. For instance, the distortion of galaxy shapes induced by the large scale structure of the Universe can be used to reconstruct the projected matter density along the line-of-sight (mass maps). Mass maps are useful as they provide a wealth of information that goes beyond and complements the more traditional two-point statistics used in Cosmology. During this talk, I will review standard techniques to reconstruct projected matter density using lensed galaxies. Then, I will discuss possible ways to use the higher order information encoded in the mass maps to constraint cosmological parameters, with a particular focus on the second and third moments of the maps. Finally, I will show some preliminary systematic tests from the first three years of observations of the Dark Energy Survey (DES Y3), which will allow to construct the largest curved-sky galaxy weak lensing mass map to date, covering about 5000 sq. deg of the southern sky.
March 27, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Star Formation Then and Now Nia Imara, Harvard University
Stars are of fundamental importance to astronomy, and how they form and shape their environments influence everything from exoplanet studies to cosmology. Stars form in heavily obscured molecular clouds, and understanding the initial conditions of star formation persists as one of the leading challenges of contemporary astrophysics. A major challenge is the wide range of physical scales involved: from the large-scale galactic environment, to molecular clouds, to the high-density filaments and cores most directly associated with the birth of stars, and all the way down to the physics of dust, atoms and molecules. I will discuss ways to overcome these challenges, focusing on the birth of molecular clouds from the atomic interstellar medium, the role of high-density substructure in the formation of stars, and the properties of molecular clouds in dwarf galaxies. I will also consider some cosmological implications of stardust, including how intergalactic dust may be a significant source of contamination in CMB spectral distortions. Throughout this presentation, I will promote the idea that bridging local star formation, extragalactic star formation, and star formation in the cosmological context will help to advance this exciting field.
April 3, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Understanding turbulent dynamo and the transport of ultra-high-energy cosmic rays using laboratory plasma astrophysics experiments Petros Tzeferacos, University of Chicago
The ubiquity of cosmical magnetic fields is revealed by diffuse radio-synchrotron emission and Faraday rotation observations. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of observable matter in the Universe and regulators of the trajectories that cosmic rays follow. The standardmodel for the origin of intergalactic magnetic fields is through the amplification of seed fields via turbulent dynamo to levels consistent with current observations. We have conceived and conducted a series of high-power laser experiments at Omega, NIF, and LMJ to study the dynamo amplification of magnetic fields in different plasma regimes. The properties of the fluid and the magnetic field turbulence are characterized using a comprehensive suite of plasma and magnetic field diagnostics. In this talk, we describe the large-scale 3D simulations we performed with the radiation-MHD code FLASH on ANL's Mira to help design and interpret the experiments. We then discuss the results of the experiments we carried out at the world's largest laser facilities, which indicate that magnetic Reynolds numbers above the expected dynamo threshold are achieved and that seed magnetic fields - produced by the Biermann battery mechanism - are amplified by turbulent dynamo. We also show how these experiments can provide experimental constrains on how cosmic rays diffuse through astrophysical magnetized turbulence.
May 1, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar A New Window into Atmospheric Escape in Exoplanets Antonija Oklopcic, Harvard-Smithsonian Center for Astrophysics
Atmospheric escape, or mass loss, is an important process in the evolution of planetary atmospheres in the Solar System, as well as in extrasolar planets. However, there are many aspects of atmospheric escape in exoplanets that remain poorly understood, in part due to a small number of direct observations. Observational evidence of atmospheric escape has been obtained only for a few exoplanets to date, mostly through transit observations in the hydrogen Lyman-alpha line, inaccessible for ground-based observations. The absorption line of helium at 10830 Angstrom can overcome some of the main difficulties associated with the UV diagnostics. In this talk, I will present a new model of escaping planetary atmospheres used to predict in-transit absorption at 10830 Angstrom. Our results indicate that significant absorption at this wavelength can be expected in some exoplanets. The helium 10830 Angstrom line is accessible for ground-based observations using high-resolution spectrographs, which could enable more detailed studies of extended atmospheres for a much larger number of exoplanets than realistically possible with UV spectroscopy. By opening up this new wavelength window into escaping atmospheres, we can improve our understanding of the physical processes that drive atmospheric mass loss and, consequently, affect planetary evolution and demographics of planetary systems.
May 8, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar DAVs: Red Edge & Outbursts Jing Luan, University of California, Berkeley
As established by ground based surveys, white dwarfs with hydrogen atmospheres pulsate as they cool across the temperature range, 12,500 K < Teff < 10,800 K. Known as DAVs or ZZ Ceti stars, their oscillations are attributed to overstable g-modes excited by convective driving. The effective temperature at the blue edge of the instability strip is slightly lower than that at which a surface convection zone appears. The temperature at the red edge is a two-decade old puzzle. Recently, the Kepler space telescope discovered a number of cool DAVs exhibiting sporadic outbursts separated by days, each lasting several hours, and releasing ~10^33-10^34 erg. We provide quantitative explanations for both the red edge and the outbursts. The minimal frequency for overstable modes rises abruptly near the red edge. Although high frequency overstable modes exist below the red edge, their photometric amplitudes are generally too small to be detected by ground based observations. Nevertheless, these overstable parent modes can manifest themselves through nonlinear mode couplings to damped daughter modes which generate limit cycles giving rise to photometric outbursts.
June 5, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Power, Privilege and Leadership in Academia Kathryn V. Johnston, Columbia University
PDF This "talk" consists of a set of slides to share what I have learned, both through my career as an academic and from perusing the social and psychological science literature, that I have found useful to understanding barriers to the full participation of women and other under-represented minorities in science. My intention is not to give a thorough review (the vast majority of the professional literature I read is on the Milky Way , not psychology!), but rather use the slides as a starting point for discussion. Participation by department members, from students to senior faculty, is welcome.
April 20, 2018 | 1:00 PM | ERC 576 | Special Seminar Come Explore with Us! Kimberly Ennico-Smith, NASA
PDF SOFIA is entering a new era of research and capability with significant new opportunities! From funding of $10,000 per hour of award observation time, to a multi-million dollar call for new groundbreaking science programs that can require updates to existing instruments or the fabrication of new instruments, there are a number of new ways to explore with the SOFIA team. This short meeting is a chance to review those funded opportunities and to learn about the new ideas you have for SOFIA. Please join us this Friday at 1PM!
May 31, 2018 | 12:00 PM | ERC 501 - Hubble Lounge | Special Seminar Focus on the Science, Not the Scientist Kenneth Sembach, Space Telescope Science Institute
Biases can play a subtle but important role in defining the outcomes of proposal peer reviews, job hiring campaigns, and manuscript reviews. In this seminar I'll describe some of the biases discovered in the proposal review process for the Hubble Space Telescope, as well as actions being taken to minimize them including anonymization of the proposers' identities during the reviews. While widely regarded as a more objective form of peer review in many fields, science reviews with hidden proposer identities are new to the field of astronomy. Proposers will face changes in the ways proposals need to be written to prevent self-identification, and reviewers will need to be cautious not to impart conscious bias into the review process by trying to determine the identities of the proposers from the information presented. This significant change in assessing Hubble proposals will be watched closely as a "pilot program" for other observatories and agencies to emulate. After describing the path forward for Hubble, we will have an open discussion about measuring progress and the pros and cons of focusing the proposal peer review process on the science proposed rather than the proposing scientists.