March 30, 2005 | 3:30 PM | RI 480 | Astronomy Colloquium Seismology of Accreting White Dwarfs Phil Arras, University of California, Santa Barbara
Pulsation modes have recently been observed in a handful of white dwarf primaries of Cataclysmic Variables, allowing an interesting new probe into the structure of accreting white dwarfs. I will briefly discuss the seismology of these objects, how stellar properties may be inferred from the observed mode frequencies, and new work on mode driving mechanisms.
April 6, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Early Structure Formation Tom Abel, Stanford University
Through a series of numerical simulations we have arrived at the conclusions that the first luminous objects in the universe were massive isolated stars. These predictions will be tested observationally in the near future. This talk will highlight some of our current attempts to extend such studies of early structure formation to the first metal enriched stars and small early galaxies.
April 13, 2005 | 3:30 PM | RI 480 | Astronomy Colloquium A Tour in the Neutron Star Zoo Rosalba Perna, University of Colorado
Neutron stars are the most common end state of stars, and hundreds of millions of them populate the Galaxy. Despite the fact that several of their properties, such as their mass and composition, vary over relatively narrow ranges, neutron stars give rise to a bewildering zoo of observational properties. In this talk, I will review the main characteristics of the various classes of neutron stars, highlighting differences and connections, and the extent to which these are due to intrinsic versus environmental properties. In particular, I will focus on the origin of the quiescent X-ray emission in Anomalous X-ray pulsars and Soft Gamma-Ray repeaters, the relation between jets in radio pulsars and their anomalous braking indices, and the ultimate fate of the large number of old, isolated neutron stars in the Galaxy. I will finally show how the statistical properties of radio pulsars associated with giant HI supershells can be used to constrain neutron stars birth parameters, and hence better understand the physics of supernova explosions.
April 20, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Recent Results from the Spitzer Space Telescope: A New View of the Infrared Universe Giovanni Fazio, Harvard University
The Spitzer Space Telescope, launched on 25 August 2003, is producing a significantly new view of the Universe at infrared wavelengths. Spitzer is the fourth and final element in NASA's Great Observatory series. It consists of an 85-cm telescope and three cryogenically-cooled instruments capable of imaging from 3 to 180 microns wavelength and spectroscopy from 5 to 40 microns wavelength. Combining the intrinsic sensitivity achievable with a cryogenic telescope in space with the high sensitivity of modern, large-area infrared detector arrays, Spitzer is providing the astronomical community with huge gains in capability for exploring the infrared Universe. Primary among Spitzer's scientific objectives are the study of the formation and evolution of galaxies in the early Universe, understanding energy sources in ultraluminous galaxies, the study of star formation and evolution, determining the structure and evolution of planetary disks around nearby stars, and exploring the nature and distribution of brown dwarfs. After a brief description of the Spitzer mission, results from Spitzer's extragalactic and galactic observational programs will be presented, showing many of Spitzerís very spectacular images.
April 27, 2005 | 3:30 PM | RI 480 | Astronomy Colloquium Raptor Observations of GRBs and Data Mining Tom Vestrand, Los Alamos National Laboratory
May 4, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Tuning into Cosmic Rays and Neutrinos Jim Beatty, Ohio State University
Cosmic rays and neutrinos with energies sensibly expressed in joules per particle have become the subject of considerable interest. Cosmic ray fluxes at these energies are low, and detectors with areas of thousands of square kilometers are needed. The existence of these ultrahigh energy cosmic rays implies the presence of a related flux of neutrinos generated by interactions with the cosmic microwave background. These neutrinos have not yet been detected, because a volumetric exposure of about 100 km^3 sr yr is required. Radio frequency techniques offer an economical approach to obtaining the large collecting power required to make progress on these problems. I will review the recent progress made in radio detection of ultra-high energy cosmic rays and neutrinos, and the prospects for the first detection of the neutrino flux by a balloon payload viewing neutrino interactions in the Antarctic ice sheet.
May 11, 2005 | 3:30 PM | RI 480 | Astronomy Colloquium Super Flare from SGR 1806-20 Kevin Hurley, University of California, Berkeley
June 1, 2005 | 3:30 PM | RI 480 | Wednesday colloquium The Cosmic Evolution of Active Galactic Nuclei Amy Barger, University of Wisconsin
Chandra detects X-rays emitted during accretion onto supermassive black holes, even when they are highly obscured. Using extensive follow-up observations of the X-ray sources detected in both deep and wide-area Chandra surveys, I will describe the cosmic evolution of the X-ray luminosity functions and the reconstruction of the accretion history of supermassive black holes.
April 1, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar The future of dark energy measurements Dragan Huterer, Kavli Institute for Cosmological Physics
Evidence for the existence of some form of dark energy -- a smooth component that causes the accelerated expansion of the universe and contributes about 70% of the total energy density -- is by now very solid. Despite thousands of published papers on the topic, however, very little progress has been made in understanding its nature and the underlying physical mechanism. In this talk I describe the prospects of several methods to measure the macroscopic properties of dark energy within the next decade. In addition to type Ia supernovae, these include weak and strong gravitational lensing, number counts of clusters of galaxies, and cosmic microwave background anisotropies. I particularly concentrate on weak gravitational lensing, describing the recent progress and challenges in controlling the systematic errors. Considering the expected sensitivity of space-based experiments that will perform these measurements, I comment on the prospects for the overall advancement of our understanding of dark energy.
April 8, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Kinematics and Dark Energy From Supernovae at z>1 Adam Reiss, StSCI
Type Ia supernovae (SNe~Ia) provide the only direct evidence for an accelerating universe and the existence of dark energy. We are in the third year of the first space-based search and follow-up campaign to find SNe Ia at z>1 using the Hubble Space Telescope to further explore the kinematics of the expanding Universe and to characterize the nature of dark energy.
April 15, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Reionization and Early Chemical Enrichment by the First Stars Jason Tumlinson, University of Chicago
The first stars hold our interest for their uniqueness and for their potential importance to galaxy formation, chemical enrichment, and feedback on the IGM. I will review recent progress in understanding the intrinsic properties and cosmological importance of zero-metallicity stars. I will discuss insights into the mass function of early stars drawn from observations of reionization at high redshift and their nucleosynthetic "fossil remnants" preserved in the most metal-poor Galactic stars. I will then describe ongoing work to integrate a detailed Galactic chemical evolution model into the CDM picture of the formation of galaxies. This new model uses all the relevant observed phenomena to jointly constrain the mass function, metallicity evolution, and epoch over which metal free stars could have formed. Finally, I will comment on the long term prospects for finding the first stars from space and from the ground.
April 22, 2005 | 12:00 PM | RI 480 | Friday noon seminar The Dark Energy Survey James Annis, FNAL
The Dark Energy Survey is a project that aims to map 5000 square-degrees near the South Galactic Cap in g,r,i,z at i > 24 starting in 2009. The survey aims to measure w to <= 5% using 4 independent techniques: cluster count evolution, weak lensing, galaxy angular power spectra, and supernovae. The talk will discuss the project science goals, the Blanco 4m telescope and the new 500 megapixel camera we are building, the LBL deep depletion CCDs, how the survey is to be conducted.
April 29, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Measuring the CMB Anisotropies with Bolometers: ACBAR, BICEP, and Beyond Chao-Lin Kuo, CalTech
I will discuss three topics in this talk, first by reporting the latest results from the Arcminute Cosmology Bolometer Array Receiver (ACBAR). Significant improvements in sensitivity over the previous data release have been achieved by a combination of more efficient analysis techniques and the inclusion of more data. Together with the CBI measurements at lower photon frequencies, and the WMAP results on large angular scales, the joint ACBAR/CBI/WMAP power spectrum represents the current best knowledge of the temperature anisotropy between l=2 and 3000. I will then give an update on the status of the BICEP experiment (Background Imaging of Cosmological Extragalactic Polarization). BICEP is operating at 100 GHz and 150 GHz at angular resolutions of 1.0 and 0.7 degree, with an array of 98 polarization-sensitive detectors. The experiment is targeting the B-mode polarization in the CMB, which is an imprint of the primordial gravitational background radiation. It is scheduled to start observing at the South Pole station later this year. Finally, I will describe the detector development efforts at JPL/Caltech, with the emphasis on the antenna-coupled transition-edge-sensor (TES) technology for next generation CMB experiments.
May 6, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Precision Cosmology in the Non-linear Regime James Taylor, Oxford University
Current precision cosmology relies on measurements of the average evolution of the universe and of the amplitude of small, localized fluctuations around this average as long as they are still growing linearly. The subsequent non-linear phase of growth, leading to the formation of virialized dark matter halos, is harder to understand analytically but has been shown to produce simple robust patterns in extensive numerical simulations of structure formation. I will discuss several possible next-generation tests of cosmology based on the internal properties of dark matter halos, including their concentration, triaxiality, spin and substructure.
May 13, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Cosmic Rays: from the lowest to the highest energies Maximo Ave, University of Chicago
Many puzzles are associated with the observed properties of the CRs from very high energies, those above 10^15 eV, and up to the highest energy ones exceeding 10^20 eV. In particular, we would like to know what causes the spectral changes observed and the changes in composition as a function of energy. We will review the status of the observations and discuss the recent developments on theoretical models. Finally, we will focus on the high energy end of the spectrum (above 10^19 eV), an energy regime that is being scanned by the Pierre Auger Observatory. Some of the recent results will be presented.
May 20, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Direct Measurements of the Composition of Cosmic Rays Jojo Boyle, University of Chicago
While the overall cosmic-ray spectrum covers an enormous range of energies, extending beyond 10^20 eV per particle, details on the composition of the cosmic rays are known for only a fraction of this range. Yet without information on the abundances and energy spectra of the individual cosmic-ray components, conclusions about the sources of these particles, and of their acceleration and transport through the Galaxy, remain tentative and controversial. Currently, measurements of the energy spectra and absolute intensities of these individual species extend to only a few thousand GeV/amu for primary nuclei and ~200 GeV/amu for secondary nuclei. These measurements support a model in which all cosmic-ray nuclei are accelerated with the same differential energy spectrum which is consistent with that from acceleration in strong shocks, probably supernovae. In an attempt to confirm this expectation and to find experimental clues for the origin of the cosmic rays at still higher energies I will report on two current balloon borne cosmic ray detectors, TRACER and CREAM, that have been developed at the University of Chicago. TRACER is designed to measure the energy spectra of primary nuclei Oxygen to Iron (Z=8->26) over the range 0.5 - >10,000 GeV/amu. TRACER was successfully flown from McMurdo, Antarctica in December 2003. CREAM can detect Protons to Iron (Z=1->26) and had a record-breaking 42-day Antarctic flight in 2004/05. Our goal with CREAM is the determination of the ratio of secondary to primary nuclei towards 1,000 GeV/amu. Combining results from TRACER and CREAM will place severe constraints on existing models for the sources of these cosmic-ray particles, and of their acceleration and transport through the Galaxy.
May 27, 2005 | 12:00 PM | RI 480 | Friday noon seminar Cluster Density Profiles from Weak Lensing in the SDSS Erin Sheldon, Kavli Institute for Cosmological Physics
I will show the latest weak lensing results from the Sloan Digital Sky Survey. We use lensing to constrain cluster density profiles in a model-independent way. We compare the measurements to "universal" mass profiles from simulations. We also constrain the mean mass-richness relation at the ~10% level over a wide range of cluster masses. I will discuss how this mass calibration can be used to constrain cosmology. I will also discuss how the density profile on scales of tens of Mpc, far outside the virial radius, can be used to constrain bias and cosmology.
June 3, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Spheroids on Steroids: Insights from a Study of Intracluster Light Anthony Gonzalez, University of Florida
I present a unifying description of the structural and kinematic properties of all spheroids embedded in dark matter halos. The intracluster stars (ICS) in galaxy clusters define spheroids that are typically 100 times the size of normal elliptical galaxies. Our analysis of these spheroids demonstrates that they lie on a "fundamental plane" as tight as that defined by normal ellipticals, but with a different slope. We attribute the difference primarily to a corresponding change in M/L within the effective radius. By expressing the M/L term in the simple derivation of the fundamental plane in terms of the velocity dispersion, and requiring that the behavior of that term mimic the observed relation between the two quantities, we simultaneously fit a surface to ellipticals, BCGs, and the ICS. The new relation fits spheroids that span three decades in effective radius. I will also show that the ICS are a significant source of metals for the intracluster medium.
June 10, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Twenty-one centimeter radiation and epoch of reionization Xiaomin Wang, Kavli Institute for Cosmological Physics
The observation of twenty-one centimeter radiation is emerging as a powerful tool to explore the end of cosmic dark age and the epoch of reionization. I will describe the mechanism, the emission power spectra, and what it can tell us about the early Universe. What we are able to learn from 21cm observations are limited by our ability to lift various contaminations from the observed signal, such as astrophysical foregrounds, noise, and redshift space distortions, etc. I will present our approach to some of these issues. I will also discuss the aspects of some upcoming and future 21cm experiments.
April 21, 2005 | 12:00 PM | AAC 123 | Special seminar Hierarchical galaxy formation and supermassive black hole feedback Brant Robertson, CfA, Harvard University
We explore the effects of feedback from growing supermassive black holes in the context of disk galaxy formation and of the black hole mass - stellar velocity dispersion (M-sigma) relation over cosmological time. We find that feedback from the growth of supermassive black holes can assuage the formation of disk galaxies in hierarchical cosmologies, connecting the M-sigma relation to the evolution of normal disk galaxies. We also explore the redshift-dependence of the M-sigma relation resulting from mergers of progenitor galaxies whose properties have been scaled in a redshift-appropriate way. Our results have a variety of implications for models of hierarchical galaxy formation.