Astrophysics Science Division Colloquium Series
Schedule: Spring 2009
Astrophysics Science Division Colloquium Series
Schedule: Spring 2009
|Through the courtesy of the speakers since 2004, some presentations are available on line.|
ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
in Bldg 21, Room 183
unless otherwise noted.
All ASD Colloquia in May will be Building 2, Room 8
Mark Devlin (University of Pennsylvania) - Where Did Half the Starlight in the Universe Go?
Host: Stephen Rinehart
C. Robert O'Dell (Vanderbilt University) - The Dynamic Orion Nebula
Alice K. Harding (NASA Goddard Space Flight Center) - First Results on Galactic Sources From the Fermi Large Area Telescope
PRESIDENT'S DAY BREAK
Zoltan Haiman (Columbia) - Formation and Detection of Supermassive Black Holes at High Redshift
Host: Robin T. Stebbins
Building 2 Room 8
Wes Traub (JPL) - Recent Results Relevant to Future Exoplanet Missions
Host: Marc Kuchner
John Wefel (LSU) - Very High Energy Cosmic Ray Spectra: A Mysterious 'Bump' in ATIC
Host: John Mitchell
Jack Burns (University of Colorado) - Astrophysics From The Moon
Host: Stephen Merkowitz
Building 3 Goett Auditorium
Eugene Chiang (Berkeley) - Planet Formation in Transitional and Debris Disks Mar 31
Bruce Macintosh (Lawrence Livermore National Laboratory) - First Images of an Extrasolar Planetary System and the Future of Direct Detection
Malcolm Coe (Southampton University) - The Amazing X-ray Binary Population of the Magellanic Clouds
Host: Robin Corbet
Tiziana Di Matteo (Carnegie Mellon University) - The Formation and Evolution of a Cosmological Population of Black Holes and Galaxies
Host: Tuck Stebbins
Joel Kastner (Rochester Institute of Technology) - Molecular and X-ray Emission from Sun-like Stars at the Epoch of Jovian Planet Building
Host: Ehud Behar
Paul Kalas (U. of CA, Berkeley) - ST Imaging of Fomalhaut: Direct detection of an exosolar planet and Kuiper Belt around a nearby star
Host: Marc Kuchner
Elena Aprile (Columbia University) - The Search for Dark Matter with the XENON Experiment
Host: Elizabeth Hays
Building 2, Room 8
Stefan Westerhoff (University of Wisconsin-Madison) - New Results from the Pierre Auger Observatory
Building 2, Room 8
Peter Michelson (Stanford) - The Fermi Gamma-ray Space Telescope: A New View of the High Energy Universe
Host: Julie McEnery
Building 2, Room 8
MEMORIAL DAY BREAK
Where Did Half the Starlight in the Universe Go?
University of Pennsylvania
Tuesday, January 27, 2009
We believe that approximately half of all the light from stars is absorbed and reprocessed by dust. The resulting emission is grey body with a temperature near 30 Kelvin. The COBE satellite made the first measurements of the resulting Far Infrared Background (FIRB), but since that time, we have been unable to resolve the background into individual galaxies. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) was designed to address this and a host of other issues. Its three bands at 250, 350, and 500 microns span the peak in emission for galaxies at z=1. I will discuss the BLAST experiment and present results from our measurements of resolved and unresolved galaxies.
The Dynamic Orion Nebula
C. Robert O'Dell
Tuesday, February 3, 2009
The nearest cradle of massive star formation, the Orion Nebula, is rapidly changing. There are strong arguments that the large-scale nebula has had its present appearance for only a few tens of thousands of years. On the smallest scale, HST time-lapse images have shown that many of the lower-mass young pre-main sequence stars have bi-polar outflows that disrupt their surroundings, with time scales down to a few years. On an intermediate scale HST images show that the intense high velocity wind from the most massive star in the cluster has excavated a central cavity. Following a presentation of the arguments for the current dynamical structure of the nebula, I will discuss how this reflects and affects continued star formation in this region.
First Results on Galactic Sources From the Fermi Large Area Telescope
Alice K. Harding
NASA Goddard Space Flight Center
Tuesday, February 10, 2009
The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST) is a pair conversion detector designed to study the gamma-ray sky in the energy range 20 MeV to >300 GeV. Since its launched June 11, 2008, Fermi has discovered several dozen new Galactic gamma-ray pulsars, as well as emission for the first time in the gamma-ray band from a Globular Cluster and an X-ray binary. In addition, several transient gamma-ray sources in the Galactic plane have been detected. About 15 of the Fermi gamma-ray pulsars are previously unknown pulsars, discovered in blind period searches, and most are not detected at any other wavelengths. I will describe these findings, as well as prospects for detecting supernova remnants and pulsar winds nebulae.
Formation and Detection of Supermassive Black Holes at High Redshift
Tuesday, February 24, 2009
Supermassive black holes (SMBHs) are common in local galactic nuclei, and SMBHs as massive as several billion solar masses already exist at redshift z=6. The earliest SMBHs may arise by Eddington-limited gas accretion and mergers of stellar mass seed BHs, left behind by the first generation of metal-free stars, or by rapid direct collapse of gas in rare special environments where the gas can avoid fragmenting into stars. I will discuss these two scenarios and how they may be distinguished in future observations. I will also discuss how it might be possible to identify coalescing SMBH binaries, based on their variable electromagnetic emission. Together with a detection by LISA of the gravitational waves they produce, these sources could be used as new probes of the nature of gravity on cosmological scales.
Recent Results Relevant to Future Exoplanet Missions
Tuesday, March 3, 2009
With over 300 exoplanets detected, and a respectable fraction of these characterized by the transit technique, we are now ready to consider what additional characterization science might be accomplished during the coming decade, if we had the resources. In the hope that we will someday find a habitable terrestrial planet around a nearby star, I will sketch what we might learn about it from direct imaging in the visible and infrared. I will give a quick review of the status of some of the proposed space mission concepts for direct imaging, and estimate what level of characterization we might expect from them.
Very High Energy Cosmic Ray Spectra: A Mysterious 'Bump' in ATIC
Louisiana State University
Tuesday, March 10, 2009
The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment was designed to study the energy spectra of galactic cosmic rays into the 100's of TeV energy region, limited only by exposure. With a steeply falling energy spectrum, VHE cosmic rays are rare, so a balloon experiment needs to fly for as long as possible. ATIC was constructed for a series of Long Duration Balloon Flights from McMurdo, Antarctica, and has made four trips to that continent resulting in three successful flights. Following a brief review of the construction and operation of the ATIC instrument and the balloon flights, results on the spectra of the primary cosmic ray components are presented with particular attention to the VHE electron spectrum which shows a mysterious 'bump' that provides evidence for a nearby source of high energy particles.
Astrophysics From The Moon
University of Colorado
Tuesday, March 17, 2009
NASA's National Space Exploration Policy calls for a return to the Moon by 2020. Unlike Apollo, the new lunar exploration initiative is to include a robust program of science of, to, and from the Moon. Astrophysics from the Moon has particular potential. The Moon is a unique platform for fundamental astrophysical measurements of gravitation, the Sun, and the Universe. Lunar laser ranging of the Earth-Moon distance provides extremely high precision constraints on General Relativity (GR) and alternative models of gravity. Current alternate theories for gravity, including those that explain dark matter and dark energy, predict deviations from GR at a level that is potentially within the grasp of the next generation of lunar laser retroreflectors. Lacking a permanent ionosphere and, on the lunar farside, shielded from terrestrial radio emissions, a low frequency (<100 MHz) radio telescope on the Moon will be an unparalleled heliospheric and astrophysical observatory. Crucial stages in particle acceleration near the Sun can be imaged and tracked. The evolution of the Universe during and before the formation of the first stars (termed the "Dark Ages") can be traced for the first time, yielding high precision cosmology constraints. I will describe both the science and the technology of these new astrophysical observatories for the lunar surface.
Planet Formation in Transitional and Debris Disks
Tuesday, March 24, 2009
Myriad processes operate in circumstellar disks to give birth to planets. New insights are afforded by transitional T Tauri disks and debris disks. Transitional disks resemble classical T Tauri disks but have central AU-sized clearings that are swept clean of dust. They age into debris disks in which the dust is entirely optically thin. The decline in optical depth almost certainly reflects the accumulation of micron-sized grains into planets. In connection with these systems we offer progress reports on several problems in disk physics, planet formation, and planet-disk interaction: (1) How do T Tauri disks accrete and dissipate? (2) As dust grains sediment to disk midplanes, what maximum densities can they achieve? Are dust concentrations large enough for planetesimals to form by gravitational instability? (3) What physics underlies the surface brightness profiles of debris disks? In particular, how can we use the observed shapes of debris disks to infer the properties of attendant planets, such as the newly imaged extrasolar planet orbiting Fomalhaut?
First Images of an Extrasolar Planetary System and the Future of Direct Detection
Lawrence Livermore National Laboratory
Tuesday, March 31, 2009
Although more than 300 extrasolar planets are now known, almost all have been detected indirectly - through radial velocity measurements or eclipses of their parent star. Direct detection - spatially resolving the planet from the star - opens up new areas of exoplanet phase space and new avenues for planet characterization. The promise of this approach was recently demonstrated with HST images of a planet orbiting Fomalhaut (Kalas et al 2008) and adaptive optics images of a three-planet system orbiting the young A star HR8799 (Marois et al 2008). I will discuss the HR8799 system in detail, including the observational techniques used, recovery of the outermost planet in archival HST data, photometry and astrometry, the interesting properties of the host star, and the implications for models of planet atmospheres and planet formation.
The HR8799 planets were detectable because they are extremely young (60 Myr) and massive (5-10 Jupiter masses.) To next major step in direct detection will be dedicated instruments such as the Gemini Planet Imager (GPI). GPI will use a 4000-actuator MEMS deformable mirror, an advanced apodized-pupil Lyot coronagraph, and ultraprecise wavefront sensing to achieve contrasts 1-2 orders of magnitude better than any current ground or space facility. I will briefly discuss the design and scientific capabilities of GPI, which is planned to have first light in 2011 on the Gemini South 8-m telescope.
The Amazing X-ray Binary Population of the Magellanic Clouds
Tuesday, April 7, 2009
The Small Magellanic Could (SMC) represents an exciting opportunity to observe the direct results of tidal interactions on star birth. One of the best indicators of recent star birth activity is the presence of significant numbers of High Mass X-ray Binaries (HMXBs) - and the SMC has them in abundance! We present results from nearly 10 years of weekly X-ray monitoring using RXTE, an extensive survey carried out using Chandra in 2006, and a wealth of ground-based optical data. Together they permit us to build a picture of a galaxy with a mass of only a few percent of the Milky Way but with a more extensive HMXB population. However, as often happens, new discoveries lead to some challenging puzzles - where are the other X-ray binaries (eg black hole systems, LMXB systems) in the SMC? And why do virtually all the SMC HMXBs have Be star companions? And yet, the XRB population of the LMC looks extremely similar to that of the Milky Way. The evidence for all this unusual stellar evolution will be presented.Malcolm Coe obtained his PhD from Imperial College, London for his work on the first British X-ray observatory, Ariel-5. Subsequently he went to work at GSFC for a couple of years using hard X-ray data from the OSO-8 satellite to probe X-ray binaries in our galaxy. In 1980 he took up a faculty position at Southampton University, UK where he has been since. Over the years he has placed great importance on using a multi-waveband approach to understanding the complex behavior of X-ray binary systems.
The Formation and Evolution of a Cosmological Population of Black Holes and Galaxies
Tiziana Di Matteo
Carnegie Mellon University
Tuesday, April 14, 2009
There is a growing observational evidence for a close connection between the formation and evolution of galaxies and of their central supermassive black holes. Motivated by this connection, we investigate the coupled formation and evolution of black holes and galaxies using state-of-the-art cosmological hydrodynamic simulations of structure formation in the Lambda-Cold Dark Matter model. Along with the gravitational evolution of dark matter, gas dynamics, cooling and star formation, the simulation follows black hole growth and associated feedback self-consistently. I will discuss black hole growth in the centers of galaxies and the impact of AGN feedback on galaxy formation.
Molecular and X-ray Emission from Sun-like Stars at the Epoch of Jovian Planet Building
Rochester Institute of Technology
Tuesday, April 21, 2009
Observations designed to establish the masses, chemistries, and longevity of the gaseous components within giant planet-building zones in the circumstellar disks orbiting pre-main sequence and young main sequence stars are necessary to understand the process of Jovian planet formation and the origins of comets and Kuiper Belt objects. These outer solar system planet-building processes may have had substantial impact (pardon the pun) on terrestrial planet formation and the emergence of life on Earth. I describe the results of X-ray and radio observations that probe the circumstellar environments of nearby (D < 100 pc) stars with ages and spectral characteristics corresponding to the ``end game'' of giant planet formation. These results point to an intimate connection between high-energy (circum)stellar radiation and the chemistry of gaseous protoplanetary disks, and suggest that giant planets should be commonplace among close binary stars.
HST Imaging of Fomalhaut: Direct detection of an exosolar planet and Kuiper Belt around a nearby star
University of California, Berkeley
Tuesday, April 28, 2009
Advances in high-contrast imaging have produced a new sample of spatially resolved debris disks with morphologies attributed to the dynamical effects of planets. I will briefly review several cases, including our recent non-detection of Beta Pictoris b using Keck adaptive optics at L-prime. Then I will focus on the case for a planetary system around the nearby A star Fomalhaut. Optical coronagraphic observations using the Advanced Camera for Surveys aboard HST shows a vast dusty debris belt offset from the star and cleanly sculpted at its inside border. Follow-up HST images have further revealed a co-moving point source with apparent orbital motion 18 AU interior to the dust belt. I will discuss both the observational and theoretical evidence that the point source is a planet with < 3 Jupiter masses, making Fomalhaut b the lowest mass planet candidate detected via direct imaging. I will give alternate explanations and discuss future plans for the detailed mapping of Fomalhaut's planet.
The Search for Dark Matter with the XENON Experiment
Tuesday, May 5, 2009
Large volume liquid xenon detectors with excellent self-shielding and background discrimination are advancing at a fast pace and promise to impact the field of dark matter direct detection in a significant way. The XENON experiment aims at probing WIMP-nucleon interactions with more than two order of magnitude sensitivity improvement over the most stringent limits reported to date. I will review the properties of liquid xenon which make it an excellent target-detector for particle dark matter and present the status and physics reach of the current phase of the program, the XENON100 experiment in final commissioning phase at the Gran Sasso Underground Laboratory.
New Results from the Pierre Auger Observatory
University of Wisconsin-Madison
Tuesday, May 12, 2009
The Pierre Auger Observatory in Malargue, Argentina, is the world's largest detector for the study of the origin of ultrahigh energy cosmic rays. The experiment stretches over 3000 km2 and measures cosmic rays with energies above 1018 eV using two complementary detector types: an array of 1600 particle detectors on the ground, and 4 fluorescence detectors overlooking the ground array from the periphery. The Observatory is now complete, and scientific data taking started already at the beginning of 2004. Among the first results is the confirmation of the so-called GZK suppression of the cosmic ray flux at the highest energies caused by the interaction of cosmic rays with the microwave background. I will review the most recent results with a special emphasis on the energy spectrum, the chemical composition of the cosmic ray flux, and the arrival direction of the highest energy cosmic rays and their possible correlation with known astrophysics sources.
The Fermi Gamma-ray Space Telescope: A New View of the High Energy Universe
Tuesday, May 19, 2009
The Fermi Gamma-ray Space Telescope was launched by NASA on June 11, 2008. The Large Area Telescope (LAT) instrument measures cosmic gamma-ray radiation in the energy range 20 MeV to >300 GeV, with supporting measurements by the Gamma-ray Burst Monitor (GBM) for gamma-ray bursts from 8 keV to 30 MeV. The LAT, with a large improvement in sensitivity, large field-of-view, and much finer angular resolution compared to previous high-energy telescopes, observes 20% of the sky at any instant and covers the entire sky every 3 hours. Fermi is providing an important window on a wide variety of high-energy phenomena, including pulsars, black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark-matter annihilations/decays and exotic relics from the Big Bang. This talk will describe results obtained during the first six months of the first year sky-survey phase of the Fermi mission.