Astrophysics Science Division Colloquium Series
Schedule: Fall 2016

Astrophysics Science Division Colloquium Series
Schedule: Fall 2016

Recent schedules:

2016, Fall 2016, Spring  
2015, Fall 2015, Spring  
2014, Fall 2014, Spring  
2013, Fall 2013, Spring 2013, Summer
2012, Fall 2012, Spring  
2011, Fall 2011, Spring  
2010, Fall 2010, Spring  

ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
in Bldg 34, Room W150 unless otherwise noted.


Aug 30 Tom Brown (STScI) - "The Quenching of the Ultra-faint Dwarf Galaxies in the Reionization Era"


Sep 6 No Colloquium
Sep 13 Special Location: B34, W120A+B
Rodolfo Montez (SAO) - "Insights into Binary Stars, Stellar Winds, and Astrophysical Plasmas from X-ray Observations of Planetary Nebulae"
Sep 19 Special Date
Joseph Howard (GSFC) - "Freeform Optics at NASA"
Sep 20 No Colloquium
Sep 27 Special Location: B34, W120
Mateusz Ruszkowski (Michigan) - "The role of cosmic rays in stellar and supermassive black hole feedback"


Oct 4 Maria Petropoulou (Purdue) - "What is the contribution of blazars to the IceCube neutrino flux?"
Oct 11 Matthew Baring (Rice) - "Diagnostics on Acceleration and Turbulence Near Shocks in Blazar Jets"
Oct 18 Jonathan Arenberg (Northrop-Grumman) - "Lessons Learned Designing, Building and Testing the Chandra Observatory"
Oct 25 Special Location: B34, W120
David Tsang (University of Maryland) - "Planetary System Evolution: Giant Planet Eccentricity & Nonconservative Dynamics"


Nov 1 Dominik Riechers (Cornell) - "Cold gas in high-z galaxies with ALMA" (tentative)
Nov 4 Special Colloqium: B34, W120
Alessandra Buonanno (Albert Einstein Institute/UMD) - "Gravitational waves review" (tentative)
Nov 8 Brian Metzger (Columbia) - "Gravitational waves and GRB" (tentative)
Nov 15 Tetsu Kitayama (Toho Univ.) - ALMA observations of SZ effect in galaxy clusters (tentative)
Nov 22 No Colloquium
Nov 29 Special Location: B34, W120
Brian Grefenstette (Caltech) - "NuSTAR observations of SNRs and the Sun" (tentative)


Dec 6 David Spergel (Princeton) - "WFIRST" (tentative)
Dec 13 Tom Barclays (NASA Ames) - Kepler Earth-sized planets (tentative)
Dec 20 Ryan Chornock (Ohio U.) - Time-domain astrophysics (tentative)
Dec 27 No Colloquium

The Quenching of the Ultra-faint Dwarf Galaxies in the Reionization Era

Tom Brown


Tuesday, Aug 30, 2016


I will present results from a Hubble Space Telescope survey of the ultra-faint dwarf galaxies. These Milky Way satellites, discovered in the Sloan Digital Sky Survey, appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in the efforts to understand the missing satellite problem. Because they are the least luminous, most dark matter dominated, and least chemically evolved galaxies known, the ultra-faint dwarfs are the best candidate fossils from the early universe. The primary goal of the survey is to measure the star-formation histories of these galaxies and discern any synchronization due to the reionization of the universe.

Insights into Binary Stars, Stellar Winds, and Astrophysical Plasmas from X-ray Observations of Planetary Nebulae

Rodolfo Montez


Tuesday, Sep 13, 2016


Planetary nebulae (PNe) provide textbook examples of astrophysical plasma and shock processes and provide essential constraints for theories of stellar evolution and the chemical enrichment of the universe. The varied shapes of PNe reveal the actions of interacting stellar winds from the late stages in the life of intermediate-mass stars, and growing evidence suggests that many PNe are the products of interacting binary star systems. As a result, studies of PNe can yield insight into other astrophysical objects governed by binary processes, such as, low mass X-ray binaries and Type Ia supernovae. Best known for their ten thousand degree optical line emission, the Chandra X-ray Observatory has established that a fraction of PNe display extended X-ray emission from shock-heated plasmas of a few million degrees and that the central stars harbor hotter than expected point-like emission from plasmas that reach tens of millions of degrees. I describe the discoveries, insights, and questions raised by Chandra observations of PNe with emphasis on those results gleaned from the Chandra Planetary Nebulae Survey (ChanPlaNS), which is the first systematic X-ray survey of PNe in the solar neighborhood.

Freeform Optics at NASA

Joseph Howard


Monday, Sep 19, 2016


Freeform optics are non-rotationally symmetric optics with large departures from a base sphere, typically from many microns to mm. They provide additional degrees of freedom to optical designs, which enable instruments with better image quality, larger fields of view, and smaller package size. The past, present, and future usage of Freeform Optics at NASA are discussed in this presentation.

The role of cosmic rays in stellar and supermassive black hole feedback

Mateusz Ruszkowski


Tuesday, Sep 27, 2016


I will discuss the role of cosmic rays in stellar and supermassive black hole feedback. I will argue that cosmic rays are likely to play a very important role across a large range of distance scales -- from the scales of individual galaxies to the scales comparable to those of cool cores of galaxy clusters.

Regarding the galactic scale feedback, I will focus on supernova and cosmic ray driven winds. Galactic outflows play an important role in galaxy evolution and, despite their importance, detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. Although cosmic rays comprise only a tiny fraction of interstellar particles by number, they carry energy comparable to that in the thermal gas. I will describe a suite of global 3D MHD numerical simulations that focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of cosmic ray streaming along the magnetic fields. Our results show that this microphysical effect can have a significant impact on the wind launching depending on the details of the plasma physics.

Regarding the feedback on galaxy cluster scales, I will discuss results from our simulations of black hole jets in cool cores of galaxy clusters including the effects of cosmic rays. I will argue that cosmic ray heating of the intracluster medium (ICM) may be a very important heating mechanism both in the tenuous and cold phases of the ICM while not violating observational constraints.

While largely an unexplored territory in the context of galactic winds and AGN feedback, cosmic ray feedback is an important process facilitating launching and efficient driving of galactic-scale winds in starburst galaxies and heating of the ICM and remains the subject of intense research.

What is the contribution of blazars to the IceCube neutrino flux?

Maria Petropoulou


Tuesday, Oct 4, 2016


The discovery of 0.1 – 2 PeV neutrinos of astrophysical origin by IceCube has opened a new window in the high-energy Universe. There are various astrophysical candidate sources, including active galactic nuclei (AGN) and starburst galaxies. Although a firm association of the detected neutrinos with one (or more) of them is still lacking, IceCube has started constraining various theoretical models. In this talk, I will present our model predictions for (i) the blazar contribution to the diffuse neutrino flux and (ii) for the possibility of detecting individual blazars as neutrino point sources. I will discuss the implications of the latest IceCube searches on the theoretical models for blazar emission.

Diagnostics on Acceleration and Turbulence Near Shocks in Blazar Jets

Matthew Baring


Tuesday, Oct 11, 2016


Acceleration at relativistic shocks is likely to be important in various astrophysical jet sources, including blazars and other radio-loud active galaxies. An important recent development for blazar science is the ability of Fermi-LAT data to pin down the power-law index of the high energy portion of emission in these sources, and therefore also the index of the underlying non-thermal particle population. This talk highlights how multiwavelength spectra including X-ray band and Fermi data can be used to probe diffusive acceleration in relativistic, oblique, MHD shocks in blazar jets. The spectral index of the non-thermal particle distributions resulting from Monte Carlo simulations of shock acceleration, and the fraction of thermal particles accelerated to non-thermal energies, depend sensitively on the particles' mean free path scale. Models of the radiative synchrotron/Compton signatures of the resulting thermal and non-thermal particle distributions are presented. Important constraints on the frequency of particle scattering and the level of field turbulence are identified for the blazars BL Lac, AO 0235+164 and Mrk 501. The possible interpretation that turbulence levels decline with remoteness from jet shocks, and a significant role for non-gyroresonant diffusion, are addressed, and analogies to heliospheric conditions are drawn.

Lessons Learned Designing, Building and Testing the Chandra Observatory

Jonathan Arenberg


Tuesday, Oct 18, 2016


Launched in 1999, the Chandra X-ray Observatory, which began its existence as the Advanced X-ray Astrophysics Facility (AXAF) has been a highly successful, productive mission. The discussion offers some of the major lessons learned by members of the Chandra Telescope team. The lessons discussed are gleaned from our experiences developing, designing, building and testing the telescope and its subsystems, with the benefit of 16+ years of hindsight and mission success. Among the topics to be discussed are the early developmental tests, known as VETA-I and VETA-II, requirements derivation, the impact of late requirements and reflection on the conservatism in the design process. This discussion will conclude with some ideas on building highly motivated and largely badgeless teams like Chandra's for future missions of all sizes.

Planetary System Evolution: Giant Planet Eccentricity & Nonconservative Dynamics

David Tsang

University of Maryland

Tuesday, Oct 25, 2016


I will discuss two topics relevant to the evolution of planetary systems, eccentricity evolution of giant planets within their natal disks, and a new nonconservative action formalism that can be used for N-body dynamics. In the first part of the talk I will show how entropy gradients within the disk can modify the non-coorbital corotation torques which dominate the eccentricity evolution for giant planets, and that when insolation heats the gap in the disk due to the giant planet, eccentricity can be pumped. This may have a signature in the existing exoplanet radial velocity data, which may bear the imprint of the disk structure as a function of metallicity. In the second part, I will briefly outline a new nonconservative variational principle that we have recently developed, which allows for nonconservative processes to be generically modeled with an action. I will demonstrate how this allows for the formulation of nonconservative (slimplectic) variational integrators: numerical integrators with the Noether charge (Energy, angular momentum etc) accuracy properties of symplectic integrators but for systems that have dissipation or other nonconservative physics (e.g. tides, radiation reaction, drag).

Maxim Markevitch
NASA Logo, National Aeronautics and Space Administration