Astrophysics Science Colloquium Series
Schedule: October - December 2005
Astrophysics Science Colloquium Series
Schedule: October - December 2005
Through the courtesy of the speakers since 2004,
most presentations are available on line.
Future schedules:
2006, First Quarter
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Past schedules:
2005, Third Quarter
2005, Second Quarter
2005, First Quarter
2004, Fourth Quarter
2004, Third Quarter
2004, Second Quarter
2004, First Quarter
2003, Fourth Quarter
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Time: 3:45 pm (Meet the Speaker at 3:30 pm) -
Location: Bldg 21, Room 183 -
unless otherwise noted.
To view the abstract of a seminar, click on the title.
Searching for Gravitational Waves with Ground-Based Detectors
John T. Whelan
Loyola University, New Orleans
Tuesday, 4 October 2005
Abstract
The use of gravitational wave observations to open a new window on the
universe is one of the main motivations for the NASA/ESA Laser
Interferometer Space Antenna (LISA). Meanwhile, an effort is underway
to make the first direct detection of gravitational waves using
ground-based detectors such as the Laser Interferometer
Gravitational-Wave Observatory (LIGO). I will describe some of the
techniques used to search for gravitational waves with ground-based
interferometric and resonant detectors, and the status of those
searches.
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Low Ionization Nuclear Emission Line Regions: The "Missing Link" in the
AGN Population
Shobita Satyapal
George Mason University
Tuesday, 11 October 2005
Abstract
With the recent discovery that virtually all local galaxies harbor
massive nuclear black holes, there is now convincing evidence that
active galactic nuclei (AGN) and normal galaxies in our local Universe
are fundamentally connected. However, the nature of this connection and
the detailed evolutionary history connecting these objects is unknown.
Low Ionization Nuclear Emission Line Regions (LINERs), defined by their
narrow optical emission lines of low ionizatation uncharacteristic of
photoionization by normal stars, may constitute a vital piece of this
puzzle, possibly representing the "missing link" between the powerful
quintessential AGN in the Universe and galaxies such as our own.
Despite several decades of intense research, there are still open
questions, including: what fraction of LINERs are truly AGN, what are
their accretion properties, and how do these quantities relate to the
properties of the host galaxy? In this talk, I will summarize recent
results from our ongoing multiwavlength investigation of LINERs and
compare them with similar observations of known AGN.
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XMM-Newton EPIC Calibration and Health Status 2005
Marcus Kirsch
XMM Project
Friday, 28 October 2005
Location: Bldg. 2 Room 8, Time: 1:30PM
Abstract
On December 10th 2004 the XMM-Newton observatory celebrated its 5th
year in orbit. Since the beginning of the mission a steady health
and contamination monitoring has been performed in combination with
regular calibration and non routine calibration observations by the
XMM-SOC and the instrument teams. We will show trend behaviour over
the 5 years especially in combination with events like solar flares and
micro-meteoroids affecting the performance of the instruments. We will
especially address the change of redistribution behaviour of the EPIC-MOS
cameras in its spatial and time components. Furthermore we will show
cross-calibration examples from our developing cross calibration archive
of XMM-Newton, Chandra and other missions.
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Energy Extraction from Rotating Black Holes
Govind Menon
Troy University
Tuesday, 1 November 2005
Abstract
Following a brief introduction to 3+1 Electrodynamics in curved
space-time, the nature of the constraint equation that arises in the
study of a force free, axis-symmetric, stationary magnetosphere will be
discussed. The relevance of the streaming function Omega and the nature
of Poloidal Surfaces will be developed from a geometric point of view.
Finally we shall present an analytic solution to the constraint equation
and discuss its physical properties.
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Cosmic Star Formation History and Deep Field X-Ray Studies
Pranab Ghosh
Tata Institute
Tuesday, 8 November 2005
Abstract
We summarize the results of CHANDRA deep field surveys and discuss
how they bear on cosmic star-formation history. We indicate the status
of our understanding of the connection between the two. We summarize
the X-ray logN-logS diagnostics from these surveys on this point. We
discuss the discriminators in current use for distinguishing between
normal/starburst galaxies and AGN. Finally, we summarize the
correlations between X-ray emission from galaxies and their emission
in other wavebands --- optical, infrared, submm, and radio --- that
indicate the diagnostic value of X-rays for probing star formation.
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Massive Black Hole Binaries from Collisional Runaways?
John Fregeau
Northwestern University
Tuesday, 15 November 2005
Abstract
Since the invention of the term "intermediate-mass black hole" 5 years
ago, observational evidence hinting at the existence of IMBHs in the
cores of dense star clusters has slowly mounted. Theoretical studies
have shown that a collisional runaway process involving massive
main-sequence stars early in the lifetime of a cluster can produce a
very massive star that may become an IMBH. However, these studies have
largely ignored the influence of primordial binaries, which are known to
populate newly born clusters in large numbers, and strongly alter the
dynamics. I will present the first results of our numerical study of
the collisional runaway process in dense clusters containing primordial
binaries, discuss the possibility of forming an IMBH binary, and the
implications for gravity wave observations.
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The Influence of Large Scale Structure on WMAP's First Year Data
Carlos Hernandez-Monteagudo
University of Pennsylvania
Tuesday, 22 November 2005
Abstract
Apart from the temperature fluctuations generated during Hydrogen
recombination at redshift 1,100, the CMB temperature anisotropies should
carry signatures of the growth and formation of the large scale structure
at much more recent epochs. Existing surveys in the radio, optical and
X-ray ranges provide means to probe the presence of (late) secondary
anisotropies in CMB data. By using two different cross-correlation
techniques in real space, we search for signatures of hot gas and an
accelerated expansion in the Universe in WMAP's first year data. We
detect and identify sources of statistically significant temperature
decrements when comparing galaxy surveys with CMB data. These decrements
are compatible with CMB photons interacting with hot electron plasma (via
Sunyaev-Zeldovich effect), and the sources to which they are associated
are either known galaxy clusters or galaxy cluster candidates in the
Zone of Avoidance. We find no evidence of diffuse hot gas in supercluster
scales, however. Regarding the late acceleration phase of the expansion
of the Universe, we develop a phase-sensitive cross-correlation method
and apply it to unveil the signal in the CMB generated by the freeze-out
of the gravitational potentials (ISW effect). The lack of correlated
signal reported enters into contradiction with previous results and
suggests that either current surveys do not trace properly potential
wells or that there is no ISW effect in WMAP's first year data.
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Nucleosynthesis in Asymptotic Giant Branch Stars
Amanda Karakas
McMaster University
Tuesday, 29 November 2005
Abstract
The Asymptotic Giant Branch is the last nuclear-burning phase for stars
with initial masses between about 0.8 to 8 solar masses, and is very
short, comprising less than 1 per cent of the main-sequence lifetime.
Nevertheless, it is on the AGB that the richest nucleosynthesis occurs for
low and intermediate mass stars. The nucleosynthesis is driven by thermal
instabilities of the helium-burning shell, the products of which are mixed
to the stellar surface by recurrent mixing episodes. Envelope burning
occurs in the most massive AGB stars, which also alters the surface
composition. In this talk, I will discuss the structure, evolution and
sites on nucleosynthesis in AGB stars. I will focus on intermediate mass
stars, over about 3 solar masses, and the nucleosynthesis of elements
lighter than iron. I will finish with a brief discussion of the major
uncertainties.
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Cosmic infared background fluctuations from deep Spitzer images and
evidence for Population III
Alexander Kashlinsky
GSFC
Tuesday, 6 December 2005
Abstract
Spatial fluctuations of the diffuse infrared background measured
with the Spitzer Space Telescope deep imaging at near-IR are found
to be significantly in excess of random instrument noise on
angular scales up to ~ 5'. Individual galaxies have
been removed down to faint levels leaving predominantly high-z
contributions to the diffuse light fluctuations from cosmological
sources. The remaining diffuse light fluctuations are not
consistent with possible instrumental effects, nor with zodiacal
light or Galactic foregrounds, and are significantly higher than
what is expected from the remaining ordinary galaxy populations.
The spectral energy distribution of the fluctuations appears to be
flat to slowly rising with wavelength between 3.6 and 8 micron. The
amplitude, color, and spatial scale of the fluctuations in the
cosmic infrared background (CIB), remaining after removal of the
identified galaxies, might arise from fainter objects located at
early cosmic times. The signal can be explained by emissions from
massive Population III stars, the first stars in the Universe. The
measurements of the fluctuations constitute evidence of an era dominated
by the massive Population III stars and set fundamental constraints on the
history of their emission production.
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Connecting Galaxy Evolution, Star Formation and the X-ray Background
David Ballantyne
University of Arizona
Tuesday, 13 December 2005
Abstract
As a result of deep hard X-ray observations by Chandra and XMM a
significant fraction of the cosmic X-ray background has been resolved
into individual sources. These objects are almost all active galactic
nuclei (AGN) and optical followup observations find that they are mostly
obscured Type 2 AGN, have Seyfert-like X-ray luminosities, and peak in
redshift at z~0.7. In this talk, I review the properties of the X-ray
background and present calculations which show that the current data
strongly supports a change to the traditional AGN unification model. I
argue that the obscuring material required for AGN unification is
regulated by star-formation within the host galaxy, and evolves with
redshift. This evolution of the obscuration implies a close relationship
between star formation and AGN fueling, most likely due to minor mergers
or interactions.
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Jerry Bonnell
