Astrophysics Science Division Colloquium Series
Schedule: Fall 2012

Astrophysics Science Division Colloquium Series
Schedule: Fall 2012

Recent schedules:

  • 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.


    Sep 25 Mario Diaz (UT Brownsville) - Educating and mentoring underrepresented minorities through competitive research at UTB's Center for Gravitational Wave Astronomy


    Oct 2 Ehud Behar (Technion) - X-Ray Absorption of High-Redshift Quasars and Gamma Ray Bursts
    Oct 16 Joe Lazio (JPL) - The Dynamic Radio Sky
    Oct 23 Huub Rottgering (Leiden) - LOFAR - Opening up a New Window on the Universe
    NOTE: Room Change - W120
    Oct 30 Brad Benson (U Chicago) - Cluster Shadows in the Microwave Sky: Discovering the Most-Massive, Distant Clusters of Galaxies using the South Pole Telescope


    Nov 6 Nadia Zakamska (JHU) - Observations of Quasar Feedback
    Nov 15
    Nov 20 Alison Peck (ALMA) - ALMA: New Windows on the submm Universe
    Nov 27 Tom Statler (Ohio University) - Photon Rockets and Killer Asteroids: Radiation Recoil as an Evolutionary Driver in the Solar System


    Dec 4 Steve Finkelstein (UT Austin) - Galaxy Evolution in the First Billion Years: How HST has Revolutionized Our View of the Universe
    Dec 11 Gene Serabyn (JPL) - Imaging Exoplanets Very Close to Bright Stars with the Vortex Coronagraph
    Dec 18 Henrique Schmitt (NRL) - The Structure of Stars, AGN Nuclei and Geostationary Satellites

    Educating and mentoring underrepresented minorities through competitive research at UTB's Center for Gravitational Wave Astronomy

    Mario Diaz

    UT Brownsville

    Tuesday, September 25, 2012


    In this talk I will briefly describe the creation and development of the CGWA at UTB and how its research portfolio as diversified over time. I will talk about the recruitment efforts to involve particularly undergraduate students in its research and the center's participation in the LIGO Scientific Collaboration and the LISA mission. I will finish the talk describing my interest in developing a program to participate in transient optical observations and the TOROS project to create such observatory in the highlands of the Argentine northwest.

    X-Ray Absorption of High-Redshift Quasars and Gamma Ray Bursts

    Ehud Behar


    Tuesday, October 2, 2012


    Soft X-ray photoelectric absorption of high-z quasars has been known for more than a decade, but its astro-physical context has remained a mystery. We have constructed the largest sample to date of more than 60 high redshift quasars (z > 0.5) selected from the XMM-Newton archive based on high photon count criteria. We analyze the measured optical depth τ at 0.5 keV for the sample, in an attempt to find which physical parameters of the quasars drive their observed absorption, e.g., redshift, radio luminosity, radio loudness, or the X-ray luminosity. Clearly, high-z quasars are more absorbed than low-z quasars, and radio-loud quasars are more absorbed than radio quiet ones. In fact, z < 2 and radio quiet objects show very little X-ray absorption, and for the most part, provide only upper limits for the optical depth. Taken at face value, optical depth does seem to steeply increase with redshift as τ ~ (1+z)2.5. We confront the quasar absorption dependence on redshift with a comparison sample of gamma ray bursts (GRBs). The 0.5 keV optical depths of both the quasars and the GRBs tend at high redshift to a value of τ ~ 0.4. Such behavior is expected if the absorption arises from the diffuse intergalactic medium (IGM). However, quasar X-ray opacity at intermediate redshift (0.5 < z < 2) is generally too low, which makes the diffuse IGM scenario unlikely.

    The Dynamic Radio Sky

    Joe Lazio


    Tuesday, October 16, 2012


    The time domain of the sky has been only sparsely explored, a fact reflected in "time domain astronomy" being recognized in the Astronomy Decadal Survey as one of five science frontier discovery areas. At radio wavelengths, recent discoveries from limited surveys, serendipitous discoveries, and followup from other wavelengths indicate that there is much to be found on timescales from nanoseconds to years and at wavelengths from meters to millimeters. The observations have revealed unexpected phenomena such as rotating radio transients and coherent pulses from brown dwarfs. Additionally, archival studies have found not-yet identified radio transients without optical or high-energy hosts. In addition to the known classes of radio transients, possible other classes of objects include extrapolations from known clases and exotica such as orphan gamma-ray burst afterglows, radio-discovered supernovae, tidally-disrupted stars, flare stars, magnetars, and even transmissions from extraterrestrial civilizations. Over the next decade, meter- and centimeter-wave radio telescopes with improved sensitivity, wider fields of view, and flexible digital signal processing will be able to explore radio transient parameter space more comprehensively and systematically.

    LOFAR - Opening up a New Window on the Universe

    Huub Rottgering


    Tuesday, October 23, 2012


    LOFAR, the Low Frequency Array, is a next-generation radio telescope that is being built in Northern Europe. It will operate at frequencies from 15 to 240 MHz (corresponding to wavelengths of 20 to 1.2 m). Its superb sensitivity, high angular resolution, large field of view and flexible spectroscopic capabilities will represent a dramatic improvement over previous facilities at these wavelengths. As such, LOFAR will carry out a broad range of fundamental astrophysical studies. The design of LOFAR has been driven by four fundamental astrophysical applications: (i) The Epoch of Reionisation, (ii) Extragalactic Surveys and their exploitation to study the formation and evolution of clusters, galaxies and black holes, (iii) Transient Sources and their association with high energy ob jects such as gamma ray bursts, and (iv) Cosmic Ray showers and their exploitation to study the origin of ultra-high energy cosmic rays. During this contribution we will first present the LOFAR project with an emphasis on the challenges faced when carrying out sensitive imaging at low radio frequencies. Subsequently, we will discuss LOFAR's capabilities to survey the low-frequency radio sky. Main aims for the planned surveys are studies of z>6 radio galaxies, diffuse emission associated with distant clusters and starbursting galaxies at z>2.

    In the second part, I will discuss in detail recent radio observations of clusters that provided important information on the impact of shocks and mergers on the general evolution of clusters. In the last years we have embarked on a large project to elucidate the relation of diffuse radio sources in clusters and properties of the ICM. Presented will be results from studies of individual clusters including the spectacular 'sausage' and 'toothbrush' clusters. These provide measurements of the properties of the shocks such as Mach numbers and magnetic field strengths. Also assisted by simulations, we then show how many parameters of merging clusters can be constrained (mass ratio, impact parameter, orientation).

    Finally, the first LOFAR observations on selected nearby clusters will presented.

    Cluster Shadows in the Microwave Sky: Discovering the Most-Massive, Distant Clusters of Galaxies using the South Pole Telescope

    Brad Benson

    U Chicago

    Tuesday, October 30, 2012


    The cosmic microwave background (CMB) is one of our most unique, and powerful, tools to study cosmology. It gives us a snapshot of the content and structure of the Universe at a time only 400,000 years after the Big Bang, while also acting as a backlight to the entire observable Universe - a mechanism that imprints the CMB with signatures of structure formation during its 14 billion year journey. I will discuss recent measurements from the South Pole Telescope (SPT), which has imaged the CMB with an unprecedented combination of depth, area, and resolution. I will give an overview of the SPT cluster survey, a new catalog of ~400 of the most massive, distant clusters in the Universe, and the latest cosmological results from the SPT survey, including: constraints on dark energy, the sum of the neutrino masses, and the number of relativistic particle species. I will also give an overview of the SPT cluster follow-up program and efforts to improve the cluster mass calibration, including large X-ray programs on Chandra and XMM, and a weak lensing program using the Magellan and Hubble telescopes. Finally, I will give the status of plans to equip the SPT with even more sensitive polarization-sensitive instruments, including the currently operating SPTpol and the future SPT-3G experiments. SPTpol and SPT-3G will make high signal-to-noise measurements of the polarization of the CMB, and will additionally expand the SPT cluster survey by over an order of magnitude.

    Observations of Quasar Feedback

    Nadia Zakamska


    Tuesday, November 6, 2012


    Black hole feedback -- the interaction between the radiation and outflows from supermassive black holes and their surrounding environments -- is routinely invoked to explain the absence of overly luminous galaxies, the observed high temperatures of intracluster medium and the black hole / bulge correlations. I will review the theoretical basis of this phenomenon, existing observational evidence for feedback in various types of active galaxies and present recent observations of our group illustrating black hole feedback in action.

    ALMA: New Windows on the submm Universe

    Alison Peck


    Tuesday, November 20, 2012


    The Atacama Large Millimeter/submillimeter Array (ALMA) is an international millimeter/submillimeter interferometer under construction in the Atacama Desert of northern Chile. ALMA is situated on a high-altitude site at 5000m elevation which provides excellent atmospheric transmission over most of the wavelength range of 0.3 to 3 mm. At the shortest planned wavelength and most extended configuration, the angular resolution of ALMA will be 5 milliarcseconds. This will give us the ability to, for example, image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars at a distance of 150 pc, or to image the redshifted dust continuum emission from evolving galaxies at epochs of formation as early as z = 10. At present, there are ~30 scientists from all over the world working at the Joint ALMA Observatory in Santiago, all of whom are assisting with Commissioning and Early Science activities, as well as carrying out their own research programs. Commissioning started in January 2010 with the achievement of phase closure, and progressed to Science Verification, making "end to end" science observations with at least 8 antennas in January 2011. ALMA is currently in the first Early Science semester, making observations in 4 receiver bands with at least 16 antennas. A second call for Early Science proposals, using longer baselines and at least 32 antennas, was issued in mid-2012. This talk will outline the types of observations possible in ALMA Early Science as well as some of the latest science results.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of Japan by the National Astronomical Observatory of Japan (NAOJ) and on behalf of North America by the National Radio Astronomy Observatory (NRAO).

    Photon Rockets and Killer Asteroids: Radiation Recoil as an Evolutionary Driver in the Solar System

    Tom Statler

    Division of Astronomical Sciences, National Science Foundation, and Astrophysical Institute, Ohio University

    Tuesday, November 27, 2012


    The recoil due to the reflection and emission of photons from a Sun-irradiated surface is a major driver of dynamical evolution for small asteroids-especially the sorts that pose an impact hazard for Earth. The net recoil force (the Yarkovsky effect) drives evolution of the orbital elements; the net recoil torque (the YORP effect) drives evolution of the spin rate and axis orientation. Both effects are sensitively dependent on the spin state; hence understanding how spins evolve under the influence of YORP is crucial for understanding how orbits evolve under the influence of Yarkovsky. Previous work showed that monolithic, rigid asteroids should follow a largely deterministic "YORP cycle," with long phases of rotational acceleration and deceleration. I will demonstrate, however, that YORP is so hypersensitive to the detailed topography of the surface that slight motions of loose material can qualitatively alter the torque and interrupt the cycle. The fact that most asteroids are probably not monolithic, but instead loosely-bound aggregates, has led to suggestions that continuous YORP acceleration may drive centrifugal mass shedding and the formation of binaries. However, we have performed the first self-consistent simulations of the YORP effect on dynamically evolving aggregates, and the results indicate that acceleration is rarely continuous. Instead, repeated reconfigurations of the body under the changing centrifugal force result in a random walk in spin rate and obliquity. This stochastic YORP evolution is qualitatively different from the YORP cycle, and, moreover, correctly predicts the distribution of orbits for asteroid families evolving under the Yarkovsky effect. These results have significant implications for binary formation and the feeding of asteroids onto Earth-crossing orbits, as well as for our understanding of the material properties of potential impactors.

    Galaxy Evolution in the First Billion Years: How HST has Revolutionized Our View of the Universe

    Steve Finkelstein

    UT Austin

    Tuesday, December 4, 2012


    The field of high-redshift galaxy evolution has experience an explosion over the past three years, thanks to the installation of the infrared-sensitive Wide Field Camera 3 on the Hubble Space Telescope. In the first few months after the servicing mission, numerous papers were published detailing the discovery of the first robust galaxy samples at z = 7 and 8, with the most distant galaxies dating only 500 million years from the Big Bang. Since that time, new deep and wide area surveys, such as the HST Multi-cycle Treasury Program CANDELS, has allowed us to take a detailed look into the properties of these galaxies. These data allow us to probe into the epoch when we expect to see galaxies vigorously building up their stellar, chemical, and dust reservoirs. I will discuss my ongoing work examining these enigmatic galaxies, first on understanding the colors of these galaxies, from which we have learned about the build-up of dust in the universe, as well as the possible presence of primordial stars. I will also show how we use these galaxies to probe the reionization of the intergalactic medium, which was likely ending around this epoch. Finally, I will detail key tests for the future, including those which can only be done with the James Webb Space Telescope.

    Imaging Exoplanets Very Close to Bright Stars with the Vortex Coronagraph

    Gene Serabyn


    Tuesday, December 11, 2012


    The imaging of faint exoplanets near bright stars requires the development of very high contrast detection techniques, and one of the most promising of the novel coronagraphic techniques is the optical vortex coronagraph. Because the optical vortex is generated by means of a transparent phase mask, observations very close to the stellar position are possible. In this talk the properties of the optical vortex coronagraph will be explored, from both the theoretical and practical points of view. Recent laboratory and observational results obtained using the vortex coronagraph will also be presented. Both theory and practice suggest a bright future for the optical vortex coronagraph, especially as its small-angle observational capability enables it to be used effectively even with modestly-sized telescopes.

    The Structure of Stars, AGN Nuclei and Geostationary Satellites

    Henrique Schmitt


    Tuesday, December 18, 2012


    With a few notable exceptions, resolving stars and their disks requires the use of optical interferometry and cannot be done with monolithic telescopes. I will present recent results on the structure of stars, circumstellar disks and binaries, obtained with the Navy Precision Optical Interferometer (NPOI) and other optical interferometers. I will also present results on the observations of the tori around the nucleus of AGNs. I will discuss some of the current developments at the NPOI, which include the commissioning of a 437 m baseline, and shorter baselines, which will allow us to resolve stars as small as 0.2mas and do a detailed study of the structure of large stars. As a final subject I will discuss the observations of geostationary satellites and the challenges involved in this work.

    Jeremy Schnittman
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