474 research outputs found
Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust
We observe significant dust-correlated emission outside of H II regions in
the Green Bank Galactic Plane Survey (-4 < b < 4 degrees) at 8.35 and 14.35
GHz. The rising spectral slope rules out synchrotron and free-free emission as
majority constituents at 14 GHz, and the amplitude is at least 500 times higher
than expected thermal dust emission. When combined with the Rhodes (2.326 GHz),
and WMAP (23-94 GHz) data it is possible to fit dust-correlated emission at
2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an
additional dust-correlated component similar to Draine & Lazarian spinning
dust. The rising component generally dominates free-free and synchrotron for
\nu >~ 14 GHz and is overwhelmed by thermal dust at \nu > 60 GHz. The current
data fulfill most of the criteria laid out by Finkbeiner et al. (2002) for
detection of spinning dust.Comment: ApJ in press. 26 pages, 11 figures, figures jpeg compressed to save
spac
Feasibility study ASCS remote sensing/compliance determination system
A short-term technical study was performed by the MSC Earth Observations Division to determine the feasibility of the proposed Agricultural Stabilization and Conservation Service Automatic Remote Sensing/Compliance Determination System. For the study, the term automatic was interpreted as applying to an automated remote-sensing system that includes data acquisition, processing, and management
Tiny scale opacity fluctuations from VLBA, MERLIN and VLA observations of HI absorption toward 3C 138
The structure function of opacity fluctuations is a useful statistical tool
to study tiny scale structures of neutral hydrogen. Here we present high
resolution observation of HI absorption towards 3C 138, and estimate the
structure function of opacity fluctuations from the combined VLA, MERLIN and
VLBA data. The angular scales probed in this work are ~ 10-200 milliarcsec
(about 5-100 AU). The structure function in this range is found to be well
represented by a power law S_tau(x) ~ x^{beta} with index beta ~ 0.33 +/- 0.07
corresponding to a power spectrum P_tau(U) ~ U^{-2.33}. This is slightly
shallower than the earlier reported power law index of ~ 2.5-3.0 at ~ 1000 AU
to few pc scales. The amplitude of the derived structure function is a factor
of ~ 20-60 times higher than the extrapolated amplitude from observation of Cas
A at larger scales. On the other hand, extrapolating the AU scale structure
function for 3C 138 predicts the observed structure function for Cas A at the
pc scale correctly. These results clearly establish that the atomic gas has
significantly more structures in AU scales than expected from earlier pc scale
observations. Some plausible reasons are identified and discussed here to
explain these results. The observational evidence of a shallower slope and the
presence of rich small scale structures may have implications for the current
understanding of the interstellar turbulence.Comment: 6 pages, 5 figures. Accepted for publication in ApJ. The definitive
version will be available at http://iopscience.iop.org
Simulated SKA maps from Galactic 3D-emission models
(Abridged) We present maps for various Galactic longitudes and latitudes at
1.4 GHz, which is the frequency where deep SKA surveys are proposed. The maps
are about 1.5 deg in size and have an angular resolution of about 1.6 arcsec.
We analyse the maps in terms of their probability density functions (PDFs) and
structure functions. Total intensity emission is more smooth in the plane than
at high latitudes due to the different contributions from the regular and
random magnetic field. The high latitude fields show more extended polarized
emission and RM structures than those in the plane, where patchy emission
structures on very small scales dominate. The RM PDFs in the plane are close to
Gaussians, but clearly deviate from that at high latitudes. The RM structure
functions show smaller amplitudes and steeper slopes towards high latitudes.
These results emerge from the fact that much more turbulent cells are passed
through by the line-of-sights in the plane. Although the simulated random
magnetic field components distribute in 3D, the magnetic field spectrum
extracted from the structure functions of RMs conforms to 2D in the plane and
approaches 3D at high latitudes. This is partly related to the outer scale of
the turbulent magnetic field, but mainly to the different lengths of the
line-of-sights.Comment: 19 pages, 15 figures, accepted for publication in Astronomy and
Astrophysics. The sizes of figures have been significantly reduced. For the
version with full resolution, see
ftp://ftp.mpifr-bonn.mpg.de/outgoing/p098wre/sun-reich.pd
G28.17+0.05: An unusual giant HI cloud in the inner Galaxy
New 21 cm HI observations have revealed a giant HI cloud in the Galactic
plane that has unusual properties. It is quite well defined, about 150 pc in
diameter at a distance of 5 kpc, and contains as much as 100,000 Solar Masses
of atomic hydrogen. The outer parts of the cloud appear in HI emission above
the HI background, while the central regions show HI self-absorption. Models
which reproduce the observations have a core with a temperature <40 K and an
outer envelope as much as an order of magnitude hotter. The cold core is
elongated along the Galactic plane, whereas the overall outline of the cloud is
approximately spherical. The warm and cold parts of the HI cloud have a
similar, and relatively large, line width of approximately 7 km/s. The cloud
core is a source of weak, anomalously-excited 1720 MHz OH emission, also with a
relatively large line width, which delineates the region of HI self-absorption
but is slightly blue-shifted in velocity. The intensity of the 1720 MHz OH
emission is correlated with N(H) derived from models of the cold core. There is
12CO emission associated with the cloud core. Most of the cloud mass is in
molecules, and the total mass is > 200,000 Solar Masses. In the cold core the
HI mass fraction may be 10 percent. The cloud has only a few sites of current
star formation. There may be about 100 more objects like this in the inner
Galaxy; every line of sight through the Galactic plane within 50 degrees of the
Galactic center probably intersects at least one. We suggest that G28.17+0.05
is a cloud being observed as it enters a spiral arm and that it is in the
transition from the atomic to the molecular state.Comment: 35 pages, inludes 12 figure
Parametric Oscillation of a Moving Mirror Driven by Radiation Pressure in a Superconducting Fabry-Perot Resonating System
A moving pellicle superconducting mirror, which is driven by radiation
pressure on its one side, and by the Coulomb force on its other side, can
become a parametric oscillator that can generate microwaves when placed within
a high-Q superconducting Fabry-Perot resonator system. A paraxial-wave analysis
shows that the fundamental resonator eigenmode needed for parametric
oscillation is the TM011 mode. A double Fabry-Perot structure is introduced to
resonate the pump and the idler modes, but to reject the parasitic anti-Stokes
mode. The threshold for oscillation is estimated based on the
radiation-pressure coupling of the pump to the signal and idler modes, and
indicates that the experiment is feasible to perform.Comment: 30 pages, 6 figures, part of proceedings of FQMT 2011 conference in
Prague, Czech Republi
Sinking islands, drowned logic; climate change and community-based adaptation discourses in Solomon Islands
Global Challenges (FSW
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