Astrophysics Science Division Colloquium Series
Schedule: Spring 2012

Astrophysics Science Division Colloquium Series
Schedule: Spring 2012

Recent schedules:

  • 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.


    Jan 24 Alan Boss (DTM, Carnegie Institution) - Kepler, Microlensing, and Direct Imaging: New Constraints on Exoplanet Formation Theories
    Host: Aki Roberge
    Jan 31 Jay Lockman (NRAO) - Making the Milky Way: Fresh News on the Continuing Saga


    Feb 7 Kevin Luhman (Pennsylvania State University) - The Formation of Brown Dwarfs and Wide Planetary Companions
    Host: Marc Kuchner
    Feb 14 Julie Comerford (University of Texas) - Dual Supermassive Black Holes as a New Observational Tracer of Galaxy Evolution
    Host: Jeremy Schnittman
    Feb 28 George Sonneborn (GSFC) - The Supernova of the Century: SN 1987A at 25


    Mar 6 Jarita Holbrook (University of Arizona) - A Discussion of Diversity in Astronomy and Astrophysics
    Host: Ann Hornschemeier
    Mar 13 Charles Gammie (University of Illinois) - QPOs from the Black Hole in the Galactic Center
    Host: Jeremy Schnittman
    Mar 20 Karl Gordon (STScI) - Dust Processing in Galaxies Due to Massive Star Formation
    Host: Eli Dwek
    Mar 27 Jason Steffen (Fermilab) - Kepler's multi-object systems
    Host: Aki Roberge


    Apr 3 Laura Chomiuk (CfA) - Constraining the Progenitors of Type Ia Supernovae in the Era of the Expanded Very Large Array
    Host: Ori Fox
    Apr 17 Tom Murphy (University of California San Diego) - Testing Gravity and Lunar Dust via Lunar Laser Ranging
    Host: Stephen Merkowitz
    Apr 24 Tess Jaffe (IRAP) - Modeling Galactic Magnetic Fields with a Self-Consistent Multi-wavelength Approach
    Host: Terri Brandt


    May 1 Fernando Atrio-Barandela (Salamanca) - Searching for Missing Baryons with WMAP and PLANCK
    Host: Sasha Kashlinsky
    May 8 Kailash Sahu (STScI) - Detecting Isolated Black Holes through Astrometric Microlensing
    Host: Jeremy Schnittman
    May 15 Stefan Funk (Stanford University) - Extreme Particle Accelerators in our Galaxy
    Host: Julie McEnery

    Kepler, Microlensing, and Direct Imaging: New Constraints on Exoplanet Formation Theories

    Alan Boss

    (DTM, Carnegie Institution

    Tuesday, January 24, 2012


    Doppler and ground-based transit searches have discovered over 700 exoplanet candidates to date. These discoveries have generally supported the core accretion mechanism for giant planet formation. However, more recent discoveries have raised questions about the core accretion mechanism as the sole mechanism for exoplanet formation. NASA's Kepler space telescope has now detected 2326 exoplanet candidates, with many of these candidates occupying an oasis in discovery space that was predicted to be a desert on the basis of population synthesis models based solely on core accretion. Similarly, ground-based microlensing surveys, as well as direct imaging detections, have demonstrated the existence of significant numbers of giant planets on orbits wide enough to be difficult to explain purely by core accretion. These new constraints on planet formation theories suggest that future population synthesis models need to consider hybrid formation mechanisms, where at least some of the giant planets are formed by the disk instability mechanism, coupled with the formation of rocky planets, hot and cold super-Earths, and some giant planets by the traditional core accretion mechanism.

    Making the Milky Way: Fresh News on the Continuing Saga

    Jay Lockman


    Tuesday, January 31, 2012


    The first part of the talk is about the Green Bank 100-meter diameter radio telescope, its dramatic origin in the collapse of the 300-foot telescope, and its unique capabilities. Some of its recent scientific programs include the search for gravitational radiation, study of Mercury's molten core, discovery of new organic molecules in interstellar space, and topics in the growth and evolution of galaxies.

    The second part of the talk will expand on the evolution of galaxies, with a focus on the Milky Way's continual need for fresh gas. Recently we have discovered that there is a large cloud in the process of merging with the Milky Way whose main body contains several million solar masses of Hydrogen. It will hit the disk in a few tens of Myr. This unique object gives us information on the evolution of the Galaxy, the structure of its gaseous halo, and the existence of dark matter halos, but its origin is still quite uncertain.

    The Formation of Brown Dwarfs and Wide Planetary Companions

    Kevin Luhman

    Pennsylvania State University

    Tuesday, February 7, 2012


    Brown dwarfs have been discovered at progressively lower masses in recent years, reaching well into the mass regime of giant planets. Meanwhile, high-contrast imaging is beginning to uncover planetary-mass companions in very large orbits around stars and brown dwarfs. It is difficult for theories of star and planet formation to explain the existence of both free-floating brown dwarfs and wide planetary companions. I will review recent observational and theoretical progress in understanding the origin of these objects. I will begin by describing the latest measurements of various properties of brown dwarfs, including their initial mass function, binarity, circumstellar environment (disks, accretion, envelopes), and spatial and velocity distributions at birth, and I will compare these data to the predictions of theories for the formation of brown dwarfs. I will then describe the observed properties of wide planetary-mass companions and the resulting constraints on their formation.

    Dual Supermassive Black Holes as a New Observational Tracer of Galaxy Evolution

    Julie Comerford

    University of Texas

    Tuesday, February 14, 2012


    Dual supermassive black holes (SMBHs) with kpc-scale separations are an expected consequence of galaxy mergers, yet surprisingly few dual SMBHs have been observed to date. I will describe the first systematic search for dual SMBHs. This search employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, and X-ray and radio observations to identify dual SMBHs that power active galactic nuclei. I will present the first batch of dual SMBHs that have been discovered with these techniques. This systematic survey will enable us, for the first time, to assemble a large observational catalog of dual SMBHs, which will provide observational constraints on the galaxy merger rate, SMBH growth via gas accretion during mergers, and SMBH coalescence.

    The Supernova of the Century: SN 1987A at 25

    George Sonneborn


    Tuesday, February 28, 2012


    Supernova 1987A in the Large Magellanic Cloud is one of the most intensively studied objects in the universe. The wealth of observations across the electromagnetic spectrum have confirmed some longstanding theories, trashed others, and stimulated new ways of modeling and studying supernovae and other transient phenomena. Now at its 25th anniversary, SN 1987A is a very young supernova remnant, a phase unobserved in any other supernova. In this talk I will discuss recent observations from the far-ultraviolet to the far-infrared with HST, the VLT, Spitzer, and the Herschel Space Observatory. These data reveal new insights into the composition, geometry, and heating of the explosion debris, the shock interaction with circumstellar material, and dust in the SN 1987A system.

    A Discussion of Diversity in Astronomy and Astrophysics

    Jarita Holbrook

    University of Arizona

    Tuesday, March 6, 2012


    In 2009, I began an NSF funded project to study women and minorityrity astronomers and their practices related to large database driven projects. This social science project uses oral history interviews as the primary means of data collection along with publicly available information about individual scientists and large database driven projects. The majority of the interviews conducted for the project focus on the Infrared Processing and Data Center (IPAC), the Large Synoptic Survey Telescope (LSST), and the Sloan Digital Sky Survey (SDSS). This presentation will review the numbers for diversity within astronomy, the current hypotheses for the lack of diversity and current strategies for increasing diversity. From the NSF project, we have learned about the professional networks, the career paths, mentoring, and the hostile environment experienced by women and minority astrophysicists. Finally, there will be an open discussions of new hypotheses and strategies to increase diversity within astronomy and astrophysics.

    QPOs from the Black Hole in the Galactic Center

    Charles Gammie

    University of Illinois

    Tuesday, March 13, 2012


    Observationally, Sgr A* is perhaps the best-understood accreting black hole: its mass and distance are known with precision, and it has been resolved on sub-event-horizon scales using millimeter VLBI. Theoretically, it is now possible to create nearly ab initio numerical models of the geometrically thick, optically thin, relativistic accretion flow that is believed to power Sgr A*. I will describe results from the models, particularly the recent discovery of high frequency quasi-periodic oscillations in model near-IR and X-ray light curves.

    Dust Processing in Galaxies Due to Massive Star Formation

    Karl Gordon


    Tuesday, March 20, 2012


    The properties of dust in nearby galaxies shows evidence for processing due to nearby massive star formation. This can be seen in the ultraviolet through analysis of the starburst galaxies observations with dust radiative transfer models and variations in Milky Way and Magellanic Clouds UV extinction curves. The processing is also be seen in the infrared through Spitzer investigations of the mid-infrared aromatic (PAH) emission from HII regions and starburst galaxies. These results indicate that dust grains can respond to their environment quickly and give clues to the nature of dust grains themselves.

    Kepler's multi-object systems

    Jason Steffen


    Tuesday, March 27, 2012


    NASA's Kepler mission has discovered over 2000 exoplanet candidates, with several hundred of these candidates orbiting in multi-object systems. In such systems dynamical interactions can cause deviations from a constant period as measured by the transit times. These transit timing variations (TTVs) can be used to characterize the various objects, detect unseen objects, and confirm the planetary nature of the candidates. I report on the various studies of the multi-object planetary systems and their TTVs from the Kepler data.

    Constraining the Progenitors of Type Ia Supernovae in the Era of the Expanded Very Large Array

    Laura Chomiuk


    Tuesday, April 3, 2012


    While there is general agreement that Type Ia Supernovae (SNe Ia) signal the destruction of accreting white dwarfs that approach the Chandrasekhar mass, the mode of this accretion and the nature of the binary companion star remain some of the greatest unsolved mysteries in stellar astrophysics. Each possible progenitor scenario is accompanied by theory that makes predictions for the circumbinary medium surrounding the accreting white dwarf, and we might therefore rule out possible progenitor systems by searching for signs of interaction between the SN Ia explosion and surrounding material. Here, we present the strongest constraints to date on such material around SNe Ia, using the unrivalled sensitivity of radio continuum observations from the Expanded Very Large Array (EVLA). However, in detail these deep limits on the density of material surrounding SNe Ia can be difficult to interpret, due to a limited empirical understanding of the environments of local accreting white dwarfs. We therefore also present our intensive EVLA campaign to monitor recent Galactic novae---local laboratories for mass transfer and accretion processes---at radio wavelengths, probing the circumbinary material in these systems with unprecedented detail and sensitivity.

    Testing Gravity and Lunar Dust via Lunar Laser Ranging

    Tom Murphy

    University of California San Diego

    Tuesday, April 17, 2012


    Forty years ago, Apollo astronauts placed the first of several retroreflector arrays on the Moon. Laser range measurements between the Earth and the Moon have provided some of our best tests to date of general relativity and gravitational phenomenology--including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravitomagnetism. A new effort called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecedented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests, as well as reveal more detail about the interior structure of the Moon. This talk will include an overview of the science goals, a demonstration of millimeter range performance, the re-discovery of the Lunokhod 1 reflector, and convincing evidence that the lunar reflectors are covered by dust. The latter part will include diffraction simulations and measurement aimed at understanding the performance of corner cube reflectors experiencing thermal gradients.

    Modeling Galactic Magnetic Fields with a Self-Consistent Multi-wavelength Approach

    Tess Jaffe


    Tuesday, April 24, 2012


    Our knowledge of the large scale structure of the magnetic fields in the Milky Way is surprisingly inaccurate, but recent and future data will allow us to make progress through studies that were not previously possible. I will describe our integrated approach that performs self-consistent modeling of the observables affected by the magnetic fields, involving processes from cosmic ray electron propagation to thermal dust grain alignment. I will summarize our results so far, on-going work, and the prospects with future data from projects such as Planck, LOFAR, and the SKA.

    Searching for Missing Baryons with WMAP and PLANCK

    Fernando Atrio-Barandela


    Tuesday, May 1, 2012


    About half the baryons in the local Universe could be in the form of a Warm Hot Intergalactic Medium (WHIM). If a large fraction of the gas is ionized, it could produce significant temperature anisotropies in the Cosmic Microwave Background (CMB), generated by the thermal and also the kinematic Sunyaev-Zeldovich effect. We have developed a theoretical framework to describe the mildly non-linear regime of the WHIM that allows us to compute its contribution to CMB anisotropies measured by WMAP and the forthcoming PLANCK data. We also discuss prospective ways of detecting this contribution by cross correlating templates constructed from galaxy catalogs with CMB data.

    Detecting Isolated Black Holes through Astrometric Microlensing

    Kailash Sahu


    Tuesday, May 8, 2012


    All stars with initial masses of larger than 20 solar mass are expected to end their lives as black holes. Yet, not a single isolated black hole has been unambiguously detected in the Galaxy. Astrometric microlensing is the only available technique capable of detecting isolated black holes and measuring their masses. I will discuss the technique of astrometric microlensing, and two HST programs underway aimed at the first detections of isolated, stellar-mass black holes through this technique.

    Extreme Particle Accelerators in our Galaxy

    Stefan Funk

    Stanford University

    Tuesday, May 15, 2012


    The past decade has brought significant advances in our understanding of acceleration processes at work in shell-type as well as in plerionic Supernova remnants through observations from radio via X-rays to VHE Gamma-rays. Unprecedented morphological studies of gamma-ray emission from shell-type Supernova remnants show a striking correlation to X ray emission. Gamma-ray energy spectra of up to 100~TeV confirm particle acceleration close to the ``knee'' in the Cosmic ray spectrum at 1~PeV in these objects. The Fermi-LAT is contributing to our understanding of these objects through observations in range between 20 MeV and 300 GeV. All these observations allow for the first time to severely constrain gamma-ray emission models and allow for studies of the parent population accelerated in these objects. I will review the current observational status of gamma-ray emission and our understanding of the origin of cosmic rays.

    Judith Racusin
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