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|Thu, Jan 15|
Los Alamos National Laboratory
" Mining the Sky in Time Domain with Telescope Networks"
Temporal changes in celestial sources populate a large parameter space ranging from continuous low-amplitude variability in stars to violent explosions such as gamma-ray bursts (GRBs) with enormous energies emitted in a matter of seconds. In recent years we have seen an accelerated progress in time domain studies enabled by a synergy between diverse wide-field survey instruments, affordable computing, and advances in information technology. The RAPTOR/Thinking Telescopes project is developing a network of fully autonomous optical imaging detectors for continuous monitoring of the night sky in search of rapid transient phenomena on time-scales as short as 1 minute. I will discuss the RAPTOR concept, implementation, and GRB science results. The overarching idea is to fuse robotic instrumentation, machine learning, and data intensive information processing to construct a distributed system capable of automatically finding interesting transients and responding before the event is over. Deep wide-field surveys operating on longer time-scales such as the Large Synoptic Survey Telescope (LSST) offer a great opportunity to explore other parts of the parameter space. At the same time, despite a substantial progress in automated variability detection and classification, optimizing the follow-up strategy given a limited pool of resources remains a challenge. The proposed dynamic coalition architecture may help to alleviate this problem.
|Thu, Jan 22|
Lawrence Berkeley National Laboratory
"The Dark Energy Spectroscopic Instrument (DESI) Survey"
The Dark Energy Spectroscopic Instrument (DESI) will perform a spectroscopic redshift survey of 24 million galaxies and quasars at the Kitt Peak National Observatory 4-m Mayall telescope from 2018–2023. These include 4M luminous red galaxies, 18M emission line galaxies, and 2.4M quasars with 0.7M Lyman-alpha forest lines-of-sight. These enable DESI to map the expansion history of the universe to redshift 3 with unprecedented accuracy using the baryon acoustic oscillation method. During bright time, DESI will observe an additional 10M nearby galaxies and 10M stars. I will describe the science reach of DESI, the new spectrographs fed by 5000 robotically positioned fiber optics, and the data systems for target selection, survey planning, simulations, and processing the data. While building off the heritage of previous galaxy redshift surveys, DESI is upgrading all aspects of the pipelines and algorithms to maximize the science reach of the new instrument and survey.
|Thu, Jan 29|
University of Colorado
"Engines, Lighthouses, and Laboratories: Massive Stars Across the Cosmos"
Massive stars are crucial building blocks in the study of star-forming galaxies, stellar evolution, and transient events, and their applications as astrophysical tools span a broad range of subfields. The radiative signatures of young star-forming galaxies are powered by their massive stellar populations. Transient phenomena act as observational beacons, ranging from local non-terminal events signaling the death throes of extreme massive stars to long-duration gamma-ray bursts that can serve as powerful probes of the high-redshift universe. Finally, resolved massive star populations offer a treasure trove of nearby targets, allowing us to closely examine their physical parameters, evolution, and contribution to chemical enrichment. I will present my current research programs focused on developing a comprehensive picture of massive stars across the cosmos: observational surveys and models of star-forming galaxies, progenitor and host environment studies of transient phenomena, and extragalactic stellar observations, including the recent discovery of the first Thorne-Zytkow object candidate. Combined, this work will make substantial progress in our understanding of massive stars over the coming decade. This in turn will equip us with the tools we need to take full advantage of the frontiers opened up by new observational facilities such as LSST, the ELTs, JWST, allowing us to immediately begin probing the new corners of the universe that they reveal.
|Thu, Feb 05|
University of Washington
"Research Frontiers of Planetary Nebulae"
Planetary Nebulae (PNe) have been very important tools in understanding C-N production rates, stellar winds, mass loss and its collimation processes, ionization structure, hydrodynamics, dust formation, non-eqilibrium molecular chemistry, and more recently as probes of galactic structure and assembly. I will be reviewing much of the recent progress across the field with emphasis on the highlights of work by my collaboration teams. The talk will focus in two areas: (1) hydrodynamic models that account for the fantastic HST images of young and active PNe, and (2) PNe as probes of M31's stellar exodisk (an extension if its classical disk from 30 to 1000 kpc).
|Thu, Feb 12|
"Toward Understanding the Formation of Proto-planetary Disks and Multiple Star Systems"
Disks and multiple star systems are thought to form early in the star formation process. Conservation of angular momentum enables the formation of protostellar disks and protostellar companions can also form if the disk is gravitationlly unstable. However, theory and simulations have suggested disk formation and multiple star formation may be difficult due to removal of angular momentum by magnetic fields. Observations are now sensitive enough to begin testing these predictions and I will present my discovery of the first rotationally-supported (Keplerian) disk around a protostar in the earliest phase of evolution. This discovery has led the way for further ALMA studies of disks in similarly young systems. Despite this recent progress, the number of known Keplerian disks around the youngest protostars remains small and the frequency of companion protostars on scales < 150 AU is unconstrained. To greatly expand our knowledge on the frequency of disks and multiplicity, I am leading a 264 hour VLA large program to observe all protostars in a single star forming region, the Perseus molecular cloud (d ~ 230 pc, N ~ 80), with a spatial resolution of 15 AU With these data, we are identifing new protostellar disk candidates and closer multiple systems than have ever been previously identified toward such young protostars. We have found evidence for a bimodal distribution of protostar separations, with a peak at ~80 AU and another at ~3000 AU. This result is suggestive of multiple formation mechanisms on different scales. Finally, we also see indications of evolution in the separation distribution for younger and more-evolved protostars. The characterization of the newly discovered multiples and disk candidates is just beginning
|Thu, Feb 19|
"Observing the Formation of Planetary Diversity"
Planets and planetary systems are incredibly diverse, as evidenced by the unique planets of our solar system, and the large variety of exoplanetary systems. How did this diversity develop? I will discuss our current understanding of how a unified planet formation scenario can explain such an array of planets, and describe the observations I have been performing to test aspects of this scenario. In particular, I will discuss how spectroscopic observations of protoplanetary disks can be used to probe such processes as disk dispersal, interactions between disks and protoplanets, and the development of the unique chemical characteristics of planets.
|Thu, Feb 26|
LPL/University of Arizona
"Small Planets, Small Stars"
Small stars and small planets are ubiquitous in the Galaxy. Planets smaller than ~2.5 Earth radii occur more frequently than any other type of planet. Stars with masses below ~0.4 Solar masses are the most common type of star. Nonetheless we know much less about the formation, evolution, interior composition, atmospheric makeup, and population trends of M dwarf planetary systems than we do for planets orbiting Sunlike stars. I will review our work to shed further light on the matter, including my team's large HST survey of transiting super-Earth atmospheres and a search for new, small planets transiting M dwarfs using NASA's new "K2" mission. These projects provide the foundation necessary to enable many future exoplanet observations with JWST and other upcoming observing facilities.
|Thu, Mar 05|
KITP/UC Santa Barbara
"The physics of stellar angular momentum transport"
Stars are born rotating. Understanding how the angular velocity profile changes during their evolution is key to unravel the details of explosive stellar deaths (Supernovae and Gamma Ray Bursts) and the properties of stellar remnants (White Dwarfs, Neutron Stars and Black Holes). In particular a large, unpredicted diversity in explosive stellar deaths has been recently highlighted by transient surveys like PTF and Pan-STARRS, pointing towards an incomplete understanding of stellar physics. In the last couple of years new exciting results have been obtained by the KEPLER satellite, which through asteroseismology has provided a measure of the degree of radial differential rotation in many evolved low-mass stars. My current research efforts combine these new observational results with theoretical and numerical modeling of stellar interiors and evolution. I will discuss the physics of different classes of angular momentum transport mechanism in stars, including rotational instabilities and circulations, magnetic torques and internal gravity waves. I will show how the asteroseismic observations can be used to test these different mechanisms in stellar evolution calculations, a synergy that thanks to upcoming observational facilities like K2, GAIA, TESS and PLATO will propel us in the era of high precision stellar physics.
|Thu, Mar 12|
University of Texas
"Simple Instruments for Complicated Physics"
It is crucial to design new astronomical instruments guided by a desire to understand astrophysics. It is easy to stumble into an engineering experiment instead. I want to address how our experiment design should lead us to the to our desired scientific output. I will begin by describing VIRUS, a new massively replicated spectrograph I am building for HETDEX (The Hobby-Eberly Dark Energy Experiment). I will discuss the overall project, design considerations, and current status. Integral field spectrographs such as VIRUS change the way we can understand many fields of astrophysics, including galaxy formation and evolution. I will introduce LRS-2, a new low resolution spectrograph spinoff from VIRUS and discuss why integral field spectroscopy provides particularly valuable insight into the baryonic distribution of the universe.
|Tue, Mar 17|
UC Santa Cruz
"Circumgalactic Matter Matters! Why the Invisible Reservoir of Gas Around Galaxies Counts in Galaxy Evolution"
Galaxies like the Milky Way are engaged in an evolving balancing act among gas supply, consumption, and removal. Many of the baryons involved in this cycle are in a phase that is difficult to observe directly -- diffuse, highly-ionized gas in the halo, aka the circumgalactic medium. Last fall, I presented observational evidence that the cool, ~10,000 K gas in the CGM of 'normal' L* galaxies can account for most of the baryons purported to be missing from dark matter halos of galaxies with M_halo ~ 10^12. In this talk I will focus on progress in developing a consistent physical model the CGM, including hydrostatic support, two-dimensional structure, possible ionization mechanisms, and how cosmological simulations fare against CGM observations. Finally, I will present future survey data that will not only address several outstanding questions related to the CGM but will ultimately enable a more complete picture of both the CGM and the cosmic web surrounding it.