Category: Old Seminars
Monday, April 30, 2018
3:30pm, CAS 502
From Exotic to Familiar: Observing Exoplanet Atmospheres in the Coming Decade
Abstract: Observations of exoplanets to date have used the Hubble and Spitzer Space Telescopes to reveal exotic exoplanet atmospheres. Substantial resources have been dedicated to characterizing the handful of planets with radii between Earth’s and Neptune’s —for which we have no counterparts in the solar system—that are accessible to current telescopes. Observations of their transmission spectra reveal a diversity of worlds, some shrouded in clouds and others with molecular features. I will discuss the types of clouds and hazes that can obscure transmission spectra, and show the effect that these thick hazes have on the thermal emission of small exoplanets. I will discuss some of my plans for new observations during the first cycle of JWST to measure the thermal emission of these planets. The new frontier of exoplanet atmosphere studies is characterizing the atmospheres of planets more familiar to Earthlings: cold gas giants and temperate Earths. I will discuss my current work to reveal the atmosphere of a cold free‐floating giant planet, and my plans for detecting a host of interesting molecules in its atmosphere with JWST. Furthermore, we will soon be able to access Earth‐sized, temperate worlds for the most favorable 3 systems orbiting the small stars. I will discuss the recent discoveries of Earth‐sized planets around bright M dwarfs and how we might use JWST to detect their atmospheres.
Monday, April 23, 2018
3:30pm, CAS 502
What Can Modeling Chemical Abundance Ratio Distributions in Dwarf Galaxies Tell Us?
MIT Kavli Institute
Abstract: The chemical abundances found in stars convey a wealth of information on stellar evolution from stellar nucleosynthesis (e.g., stellar core burning, AGB phase burning, explosive supernova phase fusion, etc.) to stellar remnant explosive nucleosynthesis (e.g., white dwarf and neutron star mergers). Their chemical abundances also convey information on their likely galactic origins, i.e., are they formed in the bulge/disk of the Milky Way (in situ) or are they originally from an accreted dwarf galaxy or major merger (ex situ)? To make use of the information stellar chemical abundances provide I have constructed semi‐analytic models of the chemical abundance ratio distributions (CARDs) found in ultra‐faint dwarf (UFD) galaxies (Lee et al. 2013) to better constrain the relative contributions to r‐process element enrichment (e.g., Barium, Europium, etc.) from core‐collapse supernova and neutron star mergers (Lee & Frebel 2018 [in prep]). These CARDs can also provide useful information for reconstructing the accretion history of Galaxy (Lee et al. 2015). In my talk, I will explain how these CARD models and statistical analysis methods can be used to gain better insights into the origins of the Galactic halo, origins of individual r‐process enhanced stars in the UFDs and the origin of r‐process elements themselves.
Space Physics Seminar
Thursday, April 26, 2018
3:30pm, CAS 502
Extending our Vision to a Galaxy of Planets
Dr. Karl Stapelfeldt
Jet Propulsion Laboratory, Caltech
Abstract: The most obvious method of studying extrasolar planets ‐ directly imaging them alongside their parent star ‐ is also the most difficult. Image contrasts exceeding a billion to one, at subarcsecond separations, are required to detect an analog of our solar system in reflected starlight. Following the charge of the Astro2010 decadal survey, the NASA Exoplanet Exploration Program (ExEP) is tasked with developing the technology and precursor science needed to realize the goals of directly imaging Earth analogs and characterizing their atmospheres for habitability and the presence of life. In this talk I will review the history of efforts to image extrasolar planets; the methods that can be used, and technical challenges that must be met to image and characterize Earth analogs; the role of exoplanet imaging on the WFIRST mission; and how ExEP and the broader community are working to make a “New Worlds” space telescope into a ready option for the 2020 decadal survey.
4/17 Berger: Rattle and Shine: Joint Detection of Gravitational Waves and Light from the Binary Neutron Star Merger GW170817
Tuesday, April 17, 2018
3:30pm, CAS 502
Rattle and Shine: Joint Detection of Gravitational Waves and Light from the Binary Neutron Star Merger GW170817
Abstract: The much‐anticipated joint detection of gravitational waves and electromagnetic radiation was achieved for the first time on August 17, 2017, for the binary neutron star merger GW170817. This event was detected by Advanced LIGO/Virgo, gamma‐ray satellites, and dozens of telescopes on the ground and in space spanning from radio to X‐rays. In this talk I will describe the exciting discovery of the optical counterpart, which in turn led to several detailed studies across the electromagnetic spectrum. The results of the observations carried out by our team include the first detailed study of a “kilonova”, an optical/infrared counterpart powered by the radioactive decay of r‐process nuclei synthesized in the merger, as well as the detection of an off‐axis jet powering radio and X‐ray emission. These results provide the first direct evidence that neutron star mergers are the dominant site for the
r‐process and are the progenitors of short GRBs. I will also describe how studies of the host galaxy shed light on the merger timescale, and describe initial constraints on the Hubble Constant from the combined GW and EM detection.
Space Physics Seminar
Friday, April 5, 2018
Characterizing Jupiter’s Auroral Acceleration Region
University of Lancaster
Abstract: At Jupiter and other magnetized planets, auroral emissions are signatures of particle acceleration above the planetary atmosphere. Juno is currently exploring
Jupiter’s auroral acceleration region; however its low altitude coverage is limited to the dusk side of the magnetosphere. We use HST images of Jupiter’s aurora using the Knight Relation and Bayesian analysis to infer the characteristics of Jupiter’s auroral
acceleration region i.e. initial energy and density of precipitating electrons, and the
location of acceleration region. We will compare our findings to Juno’s initial results.
Monday, March 26, 2018
Imaging and Filming Black Holes, with the Event Horizon Telescope.
Abstract: Does the black hole appear as a literally dark object if we take its picture on scales of its event horizon? This simple and intriguing question will be observationally addressed by an Earth-sized radio interferometer named the Event Horizon telescope (EHT). The EHT has been resolving event-horizon-scales emission in the vicinity of supermassive black holes in our Galactic Center Sgr A* and the nearby radio galaxy M87. With recent developments in its array and new interferometric imaging techniques, the EHT may be able to provide the first pictures and movies of black holes within a year from now. This talk will give an overview of the EHT and also new interferometric imaging techniques with some example applications to other radio interferometric observations such as ALMA and VLA observations of protoplanetary disks and radio stars.
Monday, March 19, 2018
Shedding New Light on Star Formation,
from Molecular Clouds to Disks.
Abstract: Star formation is a multi‐scale process. Star‐forming clouds in our galaxy have sizes of a few tens of parsecs. Dense condensations within clouds, where individual (or groups of) stars form, are smaller by more than two orders of magnitude. Circumstellar envelopes and disks are even smaller. A complete picture of the star formation process thus requires understanding the gas structure and kinematics over a very wide range of spatial scales. I will present new interferometer (sub)millimeter data that have allow us to study the star formation environment at superb resolution, over a wide range of scales ‐from the scales of giant molecular clouds (~10pc) to the scales of circumstellar envelopes and disks (~100AU). New molecular line maps of the nearest high‐mass star‐forming cloud (the Orion molecular cloud) probe a variety of structures —such as filaments, bipolar outlows, shells, bubbles, and photo‐eroded pillars ‐ that reveal the dynamic and chaotic environment where stars forms. I will also present new ALMA observations that probe the infall of dense gas onto young protostellar systems and the impact outflows have on the circumstellar envelope —the main mass reservoir of the forming star. With even higher resolution, ALMA have allowed us to study the distribution of disk sizes and masses in the Orion Nebula Cluster.
Monday, April 2, 2018
Galactic Archaeology in the Gaia Era
Abstract: One of the key objectives of modern astrophysics is to understand the formation and evolution of galaxies. In this regard, the Milky Way is a fantastic 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 been used to dissect the structure of our Galaxy. I will also explore the future of Galactic archaeology through chemical cartography.