Astrophysics Science Division Colloquium Series
Schedule: July - September 2005
Astrophysics Science Division Colloquium Series
Schedule: July - September 2005
Time: 3:45 pm (Meet the Speaker at 3:30 pm) -
Location: Bldg 2 Conference Room (Ground Floor, Rm 8) -
unless otherwise noted.
To view the abstract of a seminar, click on the title.
July |
|---|
| Sunday | Monday | Tuesday | Wednesday
| Thursday | Friday | Saturday |
|---|
| | | | | | 1 | 2 |
| 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 10 | 11 |
12 - Charles Hoopes (JHU),
The Most Ultraviolet-Luminous Galaxies Discovered by
GALEX |
13 | 14 | 15 | 16 |
| 17 | 18 |
19 |
20 | 21 | 22 | 23 |
| 24 | 25 |
26 - Ann Hornschemeier (GSFC), Dark Energy,
Dark Matter and Science with Constellation-X |
27 | 28 | 29 | 30 |
| 31 |
August |
|---|
| Sunday | Monday | Tuesday | Wednesday
| Thursday | Friday | Saturday |
|---|
| | 1 |
2 - Glen Langston (NRAO Greenbank),
A Cosmologically Distant OH absorber/emitter |
3 | 4 | 5 | 6 |
| 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| 14 | 15 |
16 - Manasse Mbonye (RIT), Non-singular
Black Hole Model as a Possible End Product of Gravitational Collapse |
17 | 18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 28 | 29 | 30 | 31 | | | |
September |
|---|
| Sunday | Monday | Tuesday | Wednesday
| Thursday | Friday | Saturday |
|---|
| | | | | 1 | 2 | 3 |
| 4 | 5 |
6 - Scott Barthelmy (GSFC), Swift, BAT, the NFIs,
and GRBs |
7 | 8 | 9 | 10 |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 |
| 18 | 19 |
20 - Eli Dwek (GSFC), The Near Infrared Background:
Interplanetary Dust or Primordial Stars? |
21 - Lynne Valencic (UNAM), A Re-examination of
UV Extinction and Diffuse Interstellar Bands |
22 | 23 | 24 |
| 25 | 26 |
27 - John Baker (GSFC), Binary Black Hole Modeling
with Numerical Relativity |
28 | 29 | 30 | |
The Most Ultraviolet-Luminous Galaxies Discovered by GALEX
Charles Hoopes
Johns Hopkins University
Tuesday, 12 July 2005
Abstract
The Galaxy Evolution Explorer (GALEX) is conducting deep and shallow
imaging surveys in the ultraviolet. These surveys show that the
population of galaxies with the largest UV luminosities is undergoing
the strongest cosmic evolution. To understand the processes driving this
evolution, we have undertaken a study of the most UV-luminous galaxies
(UVLGs) in the local universe. I will describe the properties of these
galaxies and how they compare to other galaxy populations. I will
concentrate on the high surface brightness subset of this population
(compact UVLGs), which are small galaxies with intense star formation
and properties resembling Lyman Break Galaxies at z>3. Compact UVLGs
appear to be a distinct population in the local universe, rather than
just the extreme end of the star-formation distribution. These galaxies
may prove to be useful laboratories for studying star formation in the
conditions of the early universe.
|
Dark Energy, Dark Matter and Science with Constellation-X
Ann Hornschemeier
Goddard Space Flight Center
Tuesday, 26 July 2005
Abstract
Constellation-X, with more than 100 times the collecting area of
any previous spectroscopic mission operating in the 0.25-40 keV
bandpass,
will enable high-throughput, high spectral resolution studies of sources
ranging from the most luminous accreting supermassive black holes in
the Universe to the disks around young stars where planets form.
This talk will review the updated Constellation-X science case,
released in booklet form during summer 2005. The science areas where
Constellation-X will have major impact include the exploration of the
space-time geometry of black holes spanning nine orders of magnitude in
mass and the nature of the dark energy and dark matter which govern the
expansion and ultimate fate of the Universe. Constellation-X will also
explore processes referred to as "cosmic feedback" whereby mechanical
energy, radiation, and chemical elements from star formation and black
holes are returned to interstellar and intergalactic medium, profoundly
affecting the development of structure in the Universe, and will also
probe all the important life cycles of matter, from stellar and
planetary
birth to stellar death via supernova to stellar endpoints in the form of
accreting binaries and supernova remnants. This talk will touch upon
all these areas, with particular emphasis on Constellation-X's role in
the study of Dark Energy.
|
Green Bank Telescope Observations of Fundamental Constants and Spacecraft
Glen Langston
NRAO Greenbank
Tuesday, 2 August 2005
Abstract
The 100m diameter Robert C. Byrd GBT telescope is fully operational
and has been applied to a wide variety of astronomical observations.
We summarize our measurements of the changes in fundamental constants
based on spectral lines of OH molecule from the high redshift
(z=0.764938) quasar J0134-0931.
The capabilities of the telescopes in Green Bank have application to
Goddard's Space Science priorities as well. For example, scientists
at Goddard, have used the GBT to discover two interstellar molecules,
Propanal and Propenal. The GBT has also contributed to our
understanding of the solar system, by assisting in VLBI observations
of the Huygens probe as it fell to the surface of Saturn's moon Titan.
|
A Non-Singular Black Hole Model as a Possible End-Product of
Gravitational Collapse
Mannasse Mbonye
Rochester Institute of Technology
Tuesday, 16 August 2005
Abstract
We present a non-singular black hole model as a possible
end-product of gravitational collapse. The depicted spacetime which is
type [II,(II)], by Petrov classification, is an exact solution of the
Einstein equations and contains two horizons. The equation of state in
the radial direction, is a well-behaved function of the density and
smoothly reproduces vacuum-like behavior near r=0 while tending to a
polytrope at larger r, low density, values. The final equilibrium
configuration comprises of a de Sitter-like inner core surrounded by a
family of 2-surfaces of matter fields with variable equation of state.
The fields are all concentrated in the vicinity of the radial center
r=0. The solution depicts a spacetime that is asymptotically
Schwarzschild at large r, while it becomes de Sitter-like for vanishing
r. Possible physical interpretations of the macro-state of the black
hole interior in the model are offered. We find that the possible state
admits two equally viable interpretations, namely either a
quintessential intermediary region or a phase transition in which a
two-fluid system is in both dynamic and thermodynamic equilibrium. We
estimate the ratio of pure matter present to the total energy and in
both (interpretations) cases find it to be virtually the same, being
0.83. Finally, the well-behaved dependence of the density and pressure
on the radial coordinate provides some insight on dealing with the
information loss paradox.
|
Swift, BAT, the NFIs, and GRBs
Scott Barthelmy
Goddard Space Flight Center
Tuesday, 6 September 2005
Abstract
The Swift MidEx mission was launched in Nov 2004.
Since the commissioning phase, BAT has been operating 7 months
and localized 47 GRBs (as of July 2005). The two NFI instruments,
XRT and UVOT have been operating for a slightly shorter period.
They have detected the afterglows of many of the BAT bursts as well as
making follow-up observations of INTEGRAL and HETE bursts.
I will present descriptions of the 3 instruments and results,
focusing mainly on the BAT, including some results of
the BAT all-sky hard x-ray survey.
|
The Near Infrared Background: Interplanetary Dust or Primordial Stars?
Eli Dwek
Goddard Space Flight Center
Tuesday, 20 September 2005
Abstract
The intensity of the diffuse ~ 1 - 4 micron sky emission from which
solar system and Galactic foregrounds have been subtracted is in
excess of that expected from energy released by galaxies and stars
that formed during the z < 5 redshift interval (Arendt & Dwek 2003,
Matsumoto et al. 2005). The spectral signature of this excess near-
infrared background light (NIRBL) component is almost identical to
that of reflected sunlight from the interplanetary dust cloud, and
could therefore be the result of the incomplete subtraction of this
foreground emission component from the diffuse sky maps.
Alternatively, this emission component could be extragalactic. Its
spectral signature is consistent with that of redshifted continuum
and recombination line emission from HII regions formed by the first
generation of very massive stars. In this paper we analyze the
implications of this spectral component for the formation rate of
these Population III stars, the redshift interval during which they
formed, the reionization of the universe and evolution of collapsed
halo masses. We find that to reproduce the intensity and spectral
shape of the NIRBL requires a peak star formation rate that is higher
by about a factor of 4 to 10 compared to those derived from
hierarchical models. Furthermore, an extragalactic origin for the
NIRBL leads to physically unrealistic absorption-corrected spectra of
distant TeV blazars. All these results suggest that Pop III stars
contribute only a fraction of the NIRBL intensity with zodiacal
light, star forming galaxies, and/or non-nuclear sources giving rise
to the remaining fraction.
|
A Re-examination of UV Extinction and Diffuse Interstellar Bands
Lynne Valencic
Universidad Nacional Autonoma de Mexico
Wednesday, 21 September 2005
Location: Bldg 21/Room 183A, Time: 3:15
Abstract
Since their discovery in the 1930s, the diffuse interstellar bands (DIBs)
and their carriers have proven to be enigmatic, but a concensus has been
reached that the carriers are likely to be ionized polycyclic aromatic
hydrocarbons (PAHs). Models of PAHs show that they should contribute
strongly to UV extinction in the diffuse ISM, particularly the far-UV
nonlinear rise. In order to gain a more comprehensive view of the
relationships between PAHs and UV extinction carriers, we have assembled
DIB strengths from the literature and combined it with our homogeneous
database UV extinction characteristics. We considered 4 DIB features
over more than 100 lines of sight, making it the largest sample studied
up to this point. Our results will be useful in constraining models of
UV extinction.
|
Binary Black Hole Modeling with Numerical Relativity
John Baker
Goddard Space Flight Center
Tuesday, 27 September 2005
Abstract
Binary black hole systems are expected to be key sources of observable
gravitational radiation for existing ground based gravitational wave
instruments such as the NSF's Laser Interferometer Gravitational-Wave
Observatory (LIGO), and for the space-based Laser Interferometer Space
Antenna (LISA) a joint NASA/ESA mission. The peak radiation rate from a
comparable mass binary system occurs in the binary's final moments as the
two black holes spiral together, accelerating through each other's strong
fields in a non-linear interaction governed by Einstein's gravitational
field equations. Accurate modeling of modeling of the merger process,
and consequently of the gravitational radiation waveforms produced,
requires treatment by numerically simulating Einstein's equations,
"numerical relativity." Numerical simulations of binary black hole
systems have proven particularly challenging. I will describe recent
technical advances which promise significant improvements in modeling
applications, highlighting recent achievements of Goddard's Numerical
Relativistic Astrophysics Group.
|
Jerry Bonnell
