List of Past Astronomy Colloquia : 01-Sep-2006 to 31-Dec-2006

Date:   Wednesday 06-September-2006
Speaker:   Dr. Stephen Strom (NOAO)
Title:  "Stellar Rotation: A Probe of Initial Conditions in Star-Forming Regions?"

Date:   Wednesday 13-September-2006
Speaker:   Dr. Harvey Moseley (NASA/GSFC)
Title:  "Searching for the First Stars with Spitzer and JWST"

The IRAC camera on Spitzer provides us with a surprisingly deep view of the universe, allowing us to detect L* galaxies out to z~3. I will describe a program in which we used deep images taken with IRAC to search for light from the earliest stars. By removing the light from the individually detected galaxies, we leave a background of unresolved objects. We have shown that the statistical distribution of this background is not consistent with a plausible extrapolation of the normal population of galaxies, and is thus likely to arise from first generation objects.

While no present telescope has the sensitivity to detect these objects individually, JWST, scheduled to be launched in 2013, promises to open this epoch of the universe to study. I will describe its Near Infrared Spectrometer and the microshutters which provide its multi-object capability. The microshutter array is a new technology, and our team is now completing their development. I will show the present status of the devices and the plans for their deployment on JWST.

Date:   Wednesday 20-September-2006
Speaker:   Dr. Massimo Stiavelli (STScI)
Title:  "First Light and Reionization with HST and JWST"

Date:   Wednesday 27-September-2006
Speaker:   Dr. Neil Gehrels (NASA/GSFC)
Title:  "Gamma Ray Burst Discoveries by the Swift Mission"

Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. The NASA Swift mission, in orbit since November 2004, is an innovative multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Recent results from the mission will be presented. The long-standing mystery of short GRBs is beginning to be solved in a most interesting direction. High redshift bursts have been detected to redshift z=6.3 leading to a better understanding of star formation rates at early times. GRBs have been found with giant X-ray flares occurring in their afterglow. The very nearby GRB 060218 triggered observations within minutes of the full light curve of an odd supernova Type Ic.

Date:   Wednesday 04-October-2006
Speaker:   Dr. Arsen R. Hajian (USNO)
Title:  "Upgrading the Michelson Interferometer: The Dispersed FTS"

Date:   Wednesday 11-October-2006

Date:   Wednesday 18-October-2006
Speaker:   Dr. Chuck Keeton (Rutgers U.)
Title:  "Testing Theories of Gravity with Black Hole Lensing"

Abstract: The gravitational deflection of light provided one of the first observational confirmations of general relativity. Now I am considering how gravitational lensing can provide a stronger and more fundamental test of Einstein's theory, and of intriguing new alternatives. I will introduce a rigorous and comprehensive analytical framework for black hole lensing, and use it to make concrete predictions that are testable with current or near-future technology. Here are two examples: (1) In post-post-Newtonian theories of gravity, there are universal relations among lensing observables. Observed violations of these relations would falsify all PPN models in one fell swoop. (2) In braneworld gravity, there could be many primordial black holes in our Solar System that would be detectable via "attolensing" of gamma ray bursts.

Date:   Wednesday 25-October-2006
Speaker:   Dr. Nick Gnedin (Fermilab)
Title:  "Simulating Reionization: Yesterday, Today, Tomorrow"

I will present a (biased) overview of the current status of numerical modeling of the process of Cosmic Reionization, emphasizing the rapid progress in our ability to model ever bigger volumes with ever increasing resolution. The pace for bigger simulations is not a self-fulfilling goal, though - there is a big prize just around the corner...

Date:   Wednesday 01-November-2006
Speaker:   Daniel Weedman (Cornell U.)
Title:  "Obscured AGN and Starbursts at High Redshift Discovered by Spitzer"

Observational characteristics of AGN, starbursts, and ULIRGS observed with the Infrared Spectrograph on the Spitzer Space Telescope are reviewed. A newly discovered population of very luminous, obscured sources at z ~ 2 is discussed. There are more obscured AGN at these redshifts than optically discoverable, unobscured AGN. Exceptionally luminous starburst galaxies have also been discovered at z ~ 2, but the brightest infrared sources at such redshifts are AGN.

Date:   Wednesday 08-November-2006
Speaker:   Dr. Mario Mateo (U. of Michigan)
Title:  "Plugging Away at Dark Matter"

The local dwarf spheroidal (dSph) galaxies appear to represent the bottom end of the dark matter halo distribution. They represent the survivors of what must have been building blocks of larger systems in the early Universe. It is now possible to obtain large kinematic samples in nearby dwarf galaxies that revolutionize our ability to map the gravitational potentials of these systems and to investigate other complicating factors such as the role of tides and internal substructure. I will discuss a survey of dSph kinematics based on observations with powerful new multi-object, high-resolution spectrographs on the Magellan Telescope and the MMT. We have built up unprecedentedly large samples and have developed new techniques for their analysis. In my talk, I will explore what these data and analyses tell us about the nature of the halos in these galaxies and the nature of their interactions with the Milky Way.

Date:   Wednesday 15-November-2006
Speaker:   Dr. Matija Cuk (U. of British Columbia)
Title:  "Did Earth Originally Have More Than One Moon?"

Analyses of lunar rocks returned by Apollo missions have revealed that many of the giant impact basins on the nearside are about 3.9 billion years old. These findings have given rise to the concept of "Late Heavy Bombardment" (LHB), during which the rate of impacts on the Moon went through a major spike. Shock ages of certain meteorites are also used to argue that this bombardment was system-wide. While widespread, such interpretation of the evidence is far from certain. We show that the currently available data on meteorite ages actually weigh against the LHB being system-wide, but indicate that it was restricted to the Earth-Moon system. Such a distribution of impactors argues heavily for their geocentric origin, presumably as remnants of the Moon's formation. We show that lunar Trojans can be stable for just long enough to produce the LHB, and that their escape from equilateral Lagrangian points, followed by tidal disruption, could explain all the pieces of evidence we have from the LHB. If this scenario is correct, Earth likely had three moons for the first 0.6 billion years of its existence.

Date:   Wednesday 22-November-2006
Speaker:   No Colloquium Scheduled
Title:  "Happy Thanksgiving!"

Date:   Tuesday 28-November-2006 [NOTE SPECIAL DATE]
Speaker:   Dr. Doug Hamilton (U. of Maryland)
Title:  Neptune's Satellite Triton: A Retrospective

Triton, seventh largest satellite in the Solar System, orbits Neptune in a direction opposite the planet's spin. This peculiarity, unique amongst large satellites, points to a capture origin. Two plausible theories were advanced around the time of the Voyager flybys to explain how Neptune might have snared Triton, but both require some fine tuning. Recently Craig Agnor and I have proposed a new scenario in which Neptune captures Triton from an originally heliocentric Pluto-Charon type binary. In the aftermath of this event, the original satellites of Neptune were destroyed, and most of the debris was accreted onto Triton. Over the next 100 million years, the satellite's orbit was circularized by tides raised on it by the planet, and a stunted group of new moonlets grew from the remaining rubble. Periodically during the subsequent history of the system, Triton has exerted considerable influence on these small inner satellites via three-body resonances that have elongated and tilted the moonlet orbits. In this talk I will trace the orbital history of Neptune's satellite system from Triton's dramatic capture to the present day.

Date:   Tuesday 05-December-2006 [NOTE SPECIAL DATE]
Speaker:   Dr. David Spergel (Princeton U.)
Title:  Probing the Dark Energy: Rulers and Candles

The Wilkinson Microwave Anisotropy Probe (WMAP) has made an accurate full-sky measurement of the microwave background temperature and polarization fluctuations. These measurements probe both the physics of the very early universe and the basic properties of the universe today. The WMAP measurements rigorously test our standard cosmological model and provide an accurate determination of basic comological parameters (the curvature of the universe, its matter density and composition). When combined with other astronomical measurements, the measurements contrain the properties of the dark energy and the mass of the neutrino. The observations also directly probe the physics of inflation: the current data imply that the primordial fluctuations were primarily adiabatic and nearly scale invariant.

Many key cosmological questions remain unanswered: what happened during the first moments of the big bang? what is the dark energy? what were the properties of the first stars? I will discuss the role of on-going and future CMB observations in addressing these key cosmological questions and describe how the combination of large-scale structure, supernova and CMB data can be used to address these questions.

Date:   Wednesday 06-December-2006
Speaker:   Dr. Guy Consolmagno (Vatican Observatory)
Title:  "The Real Galileo Affair and its Effects on Church/Science Relations"

Science is always shaped by what is happening in the broader society that supports it, and the science of the 17th century was no different. Speaking as a Jesuit scientist, not a professional historian, Dr. Consolmagno examines how Galileo's work challenged the science of the day, how it was shaped by the personal ambitions of the main players in the field of natural philosophy at that time, and how Galileo's standing rose and fell with the fortunes of the Spanish during the 30 Years War.

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