Astrophysics Science Division Colloquium Series
Schedule: January - March 2008
Through the courtesy of the speakers since 2004,
most presentations are available on line.
Future schedules:
2008, Second Quarter
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Past schedules:
2007, Fourth Quarter
2007, Third Quarter
2007, Second Quarter
2007, First Quarter
2006, Fourth Quarter
2006, Third Quarter
2006, Second Quarter
2006, First 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.
X-raying the Interstellar Medium
Adrienne Juett
NASA/GSFC NPP
Tuesday, January 15, 2008
Abstract
We have used photoelectric absorption features in the Chandra/HETGS
spectra of bright X-ray binaries to study the detailed spectroscopic
structure of oxygen, iron, and neon absorption in the interstellar
medium (ISM). This is the highest-resolution X-ray spectral study of
interstellar absorption ever performed, revealing previously
undetected features and demonstrating the inadequacy of existing
models for grating data. We find that the ISM absorption edges are
well described by the neutral, atomic cross-section calculations and
laboratory measurements, although requiring small (<50 mA) shifts to
the wavelength scales. The high-resolution spectra allow us to make
an independent determination of the relative abundances of the
elements. The K-shell edges of oxygen and neon also include
absorption lines from singly and doubly ionized forms; we are able to
measure the large-scale ionization fractions of oxygen and neon in the
ISM. Finally, we will present new results from a comparison of the
ultraviolet and X-ray absorption properties of the ISM. The combined
data allows us to determine the abundances relative to hydrogen and
constrain the depletion of metals without using the abundance
assumptions inherent in ultraviolet only studies.
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Eta Carina - What we know and what we will test
Ted Gull
NASA/GSFC
Tuesday, January 22, 2008
Abstract
Eta Carina is a massive binary wind system with historical ejecta that
originated from at least one of the companions at the end of its
hydrogen-burning phase. The binary undergoes X-ray and spectroscopic
minima every 5.54 years with the next minimum predicted to be in
mid-January 2009. We intend to gather observations before, during and
after this minimum to test models of the winds and the massive ejecta
thrown out in two observed events in the 19th century.
Moreover, the N-rich, C- and O-depleted ejecta includes abundant lines
of metals including V, Sr and Sc. Why? What dust formed with a paucity
of C and O? Ultimately how much mass has been ejected and does this
system provide insight to the massive progenitors of the long GRBs?
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SN1987A X-ray and IR analysis of the "big crash"
Eli Dwek
NASA/GSFC
Tuesday, January 29, 2008
Abstract
Multiwavelength observations of supernova remnant (SNR) 1987A show that
its morphology and luminosity are rapidly changing at X-ray, optical,
infrared, and radio wavelengths as the blast wave from the explosion
expands into the circumstellar equatorial ring (ER), produced by mass
loss from the progenitor star.
The Infrared emission arises from dust particles in the ER that are
collisionally-heated by the X-ray emitting plasma.
In this talk I will present combined IR and X-ray observations of the
interaction between the SN blast wave and the ER, and show what we can
learn from the evolution of the IR-to-X-ray flux ratio about the
physical conditions of the X-ray emitting plasma and the interaction
of the dust particles with the hot gas.
Multiwavelength observations of supernova remnant (SNR) 1987A show that
its morphology and luminosity are rapidly changing at X-ray, optical,
infrared, and radio wavelengths as the blast wave from the explosion
expands into the circumstellar equatorial ring (ER), produced by mass
loss from the progenitor star.
The Infrared emission arises from dust particles in the ER that are
collisionally-heated by the X-ray emitting plasma.
In this talk I will present combined IR and X-ray observations of the
interaction between the SN blast wave and the ER, and show what we can
learn from the evolution of the IR-to-X-ray flux ratio about the
physical conditions of the X-ray emitting plasma and the interaction
of the dust particles with the hot gas.
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The Apollo LLR project
James Battat
Smithsonian Astrophysical Observatory
Tuesday, February 19, 2008
Abstract
TBD
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Measuring the Abundances of Exotic Elements in Planetary Nebulae
Nick Sterling
NASA/GSFC
Tuesday, February 12, 2008
Abstract
In recent years, trans-iron elements have been detected in the UV,
optical, and IR spectra of more than 100 planetary nebulae (PNe). These
"neutron(n)-capture" elements are of particular interest because they
can be produced by s-process nucleosynthesis in the asymptotic giant
branch (AGB) progenitors of PNe. Most of the n-capture elements that
have been detected in PNe are not accessible in the spectra of evolved
stars, and hence nebular spectroscopy provides a unique opportunity to
study enrichments of these species in one of their sites of synthesis
for the first time. Accurately determining the abundances of these
species in PNe also provides important new constraints to models of AGB
star structure and nucleosynthesis, particularly the efficiency of
convective mixing and dredge-up and the physical conditions under which
s-process nucleosynthesis occurs.
I will review recent UV and IR studies of s-process enrichments in PNe,
in which the abundances of Ge, Se, and Kr were determined in over 100
PNe. In addition, I will discuss an ongoing project to obtain deep,
high-resolution optical spectra of PNe in order to detect multiple ions
of Kr and several other n-capture elements (including Br, Xe, and Rb).
Because of the low cosmic abundances of n-capture elements (< few 10^-9
that of H), many challenges exist in the analysis of their spectroscopic
features. Foremost among these challenges are the weakness of emission
lines from these species, which causes only one or two ions from each of
these elements to be detectable in most PNe. It is therefore important
to accurately estimate the abundances of unobserved ionization stages, a
goal that requires accurate data for atomic processes affecting the
ionization balance - data which is currently unknown for nearly all
n-capture elements. I will discuss ongoing experimental and theoretical
efforts to determine the photoionization cross-sections and rate
coefficients for various recombination processes for ions of the four
most widely observed n-capture elements in PNe (Se, Kr, Xe, and Ge).
These new atomic data will be incorporated into state-of-the-art
photoionization codes in order to model the ionization structure of
n-capture elements observed in ionized nebulae, and accurately determine
their abundances.
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The NEXT / SXS Mission
Richard Kelley
NASA/GSFC
Tuesday, February 26, 2008
Abstract
The Japan Aerospace Exploration Agency's (JAXA) New Exploration X-Ray
Telescope (NEXT) is now under development for launch in 2013. The
observatory is designed to provide extremely high spectral resolution
with large collecting area below 10 keV using an x-ray calorimeter and
a very large band pass (up to 300 keV) with extraordinary sensitivity
over the range 10-80 keV using focusing x-ray optics. In this talk I
will give an overview of the mission and discuss plans for the Soft
X-Ray Spectrometer (SXS), which uses an x-ray calorimeter array to
provide the high spectral resolution. The SXS will use a 6x6
calorimeter array that has strong heritage in the Suzaku program with
better than 7 eV energy resolution, and probably as good as 4-5 eV
expected based on recent laboratory tests. The cryogenic system will
be a hybrid design developed by ISAS/JAXA with both liquid helium and
mechanical coolers to provide a robust, redundant system with long
life (> 3 years). The x-ray optical system uses thin-foil conical
optics to provide at least 220 square cm at 6 keV. The SXS will enable
a wide variety of interesting science topics to be pursued, including
testing theories of structure formation using velocity measurements of
clusters of galaxies and inferring the energy output from the jets and
winds of active galaxies. The SXS will accurately measure metal
abundances in the oldest galaxies, providing unique information on the
origin of the elements, and observe matter in extreme gravitational
fields, enabling time-resolved spectra from material approaching the
event horizon of a black hole.
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Black Hole Kick Predictions
Cole Miller
University of Maryland College Park
Tuessday, March 4, 2008
Abstract
TBD
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One Hundred 30 Dors: Is the Milky Way Different or Are We Somehow
Missing Them?
Margaret Hanson
U. Cincinnati
Tuesday, March 4, 2008
Abstract
There are a few ways to estimate the number of massive open clusters
expected in the disk of the Milky Way, such as the total star
formation rate of the Galaxy, or the open cluster mass function
extrapolated to include the entire Galaxy. Surprisingly, they give
similar predictions: the Milky Way should contain about 100 clusters
as massive as 30 Doradus in the Large Magellanic Cloud, and even
several clusters with 10 times that mass. Why donÕt we see them? This
talk will first look closely at these predictions and compare that to
what we have found so far in our Galaxy. I will then present
sophisticated Monte Carlo imaging simulations our group is doing to
estimate the selection biases faced by current near-infrared searches
for these massive clusters.
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Cometary X-rays
Dennis Bodewits
NASA/GSFC NPP
Tuesday, March 18, 2008
Abstract
The interaction of the solar wind with the planets, moons and the
interstellar medium is of key importance for understanding the evolution
of our solar system. The interaction with Earth’s atmosphere is best
known for the northern light. In case of Mars, the interaction with the
solar wind might have lead to the erosion of its atmosphere. Solar
wind-atmosphere interactions can be studied particularly well in
cometary atmospheres, because in that case the solar wind flow is not
attenuated by a planetary magnetic field and interacts directly with its
atmosphere, the coma.
When solar wind ions fly through an atmosphere they are neutralized via
charge exchange reactions with the neutral gaseous species. These
reactions depend strongly on target species and collision velocity. The
resulting X-ray and Far-UV emission can therefore be regarded as a
fingerprint of the underlying reaction, with many diagnostic qualities.
This seminar will address all aspects relevant for X-ray and FUV
emission from comets: experimental studies of state-to-state charge
exchange cross sections, observations of X-ray emission from comets
using Chandra, XMM, and Swift, and theoretical modeling of the
interaction of solar wind ions with cometary atmospheres and the
resulting X-ray emission spectrum.
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Cancelled
Mark Trodden
Syracuse University
Wednesday, March 26, 2008
Abstract
Talk Cancelled
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Randall Smith
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