2,247 research outputs found
Identifications and SEDs of the detected sources from the AKARI Deep Field South
In order to find counterparts of the detected objects in the AKARI Deep Field
South (ADFS) in all available wavelengths, we searched public databases (NED,
SIMBAD and others). Checking 500 sources brighter than 0.0482 Jy in the AKARI
Wide-S band, we found 114 sources with possible counterparts, among which 78
were known galaxies. We present these sources as well as our first attempt to
construct spectral energy distributions (SEDs) for the most secure and most
interesting sources among them, taking into account all the known data together
with the AKARI measurements in four bands.Comment: 4 pages, 10 figures, To appear in: the proceedings of the conference
"AKARI, a light to illuminate the misty Universe", February 16-19 2009, Toky
Oxygen permeation modelling of perovskites
A point defect model was used to describe the oxygen nonstoichiometry of the perovskites La0.75Sr0.25CrO3, La0.9Sr0.1FeO3, La0.9Sr0.1CoO3 and La0.8Sr0.2MnO3 as a function of the oxygen partial pressure. Form the oxygen vacancy concentration predicte by the point defect model, the ionic conductivity was calculated assuming a vacancy diffusion mechanism. The ionic conductivity was combined with the Wagner model for the oxidation of metals to yield an analytical expression for the oxygen permeation current density as a function of the oxygen partial pressure gradient. A linear boundary condition was used to show the effect of a limiting oxygen exchange rate at the surface
A new application of emulsions to measure the gravitational force on antihydrogen
We propose to build and operate a detector based on the emulsion film
technology for the measurement of the gravitational acceleration on antimatter,
to be performed by the AEgIS experiment (AD6) at CERN. The goal of AEgIS is to
test the weak equivalence principle with a precision of 1% on the gravitational
acceleration g by measuring the vertical position of the anni- hilation vertex
of antihydrogen atoms after their free fall in a horizontal vacuum pipe. With
the emulsion technology developed at the University of Bern we propose to
improve the performance of AEgIS by exploiting the superior position resolution
of emulsion films over other particle de- tectors. The idea is to use a new
type of emulsion films, especially developed for applications in vacuum, to
yield a spatial resolution of the order of one micron in the measurement of the
sag of the antihydrogen atoms in the gravitational field. This is an order of
magnitude better than what was planned in the original AEgIS proposal.Comment: 17 pages, 14 figure
Nationwide Investigation of the Pyrethroid Susceptibility of Mosquito Larvae Collected from Used Tires in Vietnam
Pyrethroid resistance is envisioned to be a major problem for the vector control program since, at present, there are no suitable chemical substitutes for pyrethroids. Cross-resistance to knockdown agents, which are mainly used in mosquito coils and related products as spatial repellents, is the most serious concern. Since cross-resistance is a global phenomenon, we have started to monitor the distribution of mosquito resistance to pyrethroids. The first pilot study was carried out in Vietnam. We periodically drove along the national road from the north end to the Mekong Delta in Vietnam and collected mosquito larvae from used tires. Simplified susceptibility tests were performed using the fourth instar larvae of Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. Compared with the other species, Ae. aegypti demonstrated the most prominent reduction in susceptibility. For Ae. aegypti, significant increases in the susceptibility indices with a decrease in the latitude of collection points were observed, indicating that the susceptibility of Ae. aegypti against d-allethrin was lower in the southern part, including mountainous areas, as compared to that in the northern part of Vietnam. There was a significant correlation between the susceptibility indices in Ae. aegypti and the sum of annual pyrethroid use for malaria control (1998–2002). This might explain that the use of pyrethroids as residual treatment inside houses and pyrethroid-impregnated bed nets for malaria control is attributable to low pyrethroid susceptibility in Ae. aegypti. Such insecticide treatment appeared to have been intensively administered in the interior and along the periphery of human habitation areas where, incidentally, the breeding and resting sites of Ae. aegypti are located. This might account for the strong selection pressure toward Ae. aegypti and not Ae. albopictus
Star-galaxy separation by far-infrared color-color diagrams for the AKARI FIS All-Sky Survey (Bright Source Catalogue Version beta-1)
To separate stars and galaxies in the far infrared AKARI All-Sky Survey data,
we have selected a sample with the complete color information available in the
low extinction regions of the sky and constructed color-color plots for these
data. We looked for the method to separate stars and galaxies using the color
information. We performed an extensive search for the counterparts of these
selected All-Sky Survey sources in the NED and SIMBAD databases. Among 5176
objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way
stars, 50 other Galactic objects, and 101 sources detected before in various
wavelengths but of an unknown origin. 22 sources were left unidentified. Then,
we checked colors of stars and galaxies in the far-infrared flux-color and
color-color plots. In the resulting diagrams, stars form two clearly separated
clouds. One of them is easy to be distinguished from galaxies and allows for a
simple method of excluding a large part of stars using the far-infrared data.
The other smaller branch, overplotting galaxies, consists of stars known to
have an infrared excess, like Vega and some fainter stars discovered by IRAS or
2MASS. The color properties of these objects in any case make them very
difficult to distinguish from galaxies. We conclude that the FIR color-color
diagrams allow for a high-quality star-galaxy separation. With the proposed
simple method we can select more that 95 % of galaxies rejecting at least 80 %
of stars.Comment: 20 pages, 41 figures, "Astronomy & Astrophysics", accepted, to appear
in the AKARI special issu
A Search for Near-Infrared Emission From the Halo of NGC 5907 at Radii of 10 kpc to 30 kpc
We present a search for near-infrared (3.5-5 micron) emission from baryonic
dark matter in the form of low-mass stars and/or brown dwarfs in the halo of
the nearby edge-on spiral galaxy NGC 5907. The observations were made using a
256 by 256 InSb array with a pixel scale of 17" at the focus of a
liquid-helium-cooled telescope carried above the Earth's atmosphere by a
sounding rocket. In contrast to previous experiments which have detected a halo
around NGC 5907 in the V, R, I, J and K bands at galactic radii 6kpc < r <
10kpc, our search finds no evidence for emission from a halo at 10kpc < r <
30kpc. Assuming a halo mass density scaling as r^(-2), which is consistent with
the flat rotation curves that are observed out to radii of 32kpc, the lower
limit of the mass-to-light ratio at 3.5-5 microns for the halo of NGC 5907 is
250 (2 sigma) in solar units. This is comparable to the lower limit we have
found previously for NGC 4565 (Uemizu et al. 1998). Based on recent models, our
non-detection implies that hydrogen- burning stars contribute < 15% of the mass
of the dark halo of NGC 5907. Our results are consistent with the previous
detection of extended emission at r < 10kpc if the latter is caused by a
stellar population that has been ejected from the disk because of tidal
interactions. We conclude that the dark halo of NGC 5907, which is evident from
rotation curves that extend far beyond 10kpc, is not comprised of hydrogen
burning stars.Comment: 12 pages, LateX, plus 6 ps figures. Accepted by ApJ. minor changes,
added references, corrected typo
Far-infrared imaging of post-AGB stars and (proto)-planetary nebulae with the AKARI Far-Infrared Surveyor
By tracing the distribution of cool dust in the extended envelopes of
post-AGB stars and (proto)-planetary nebulae ((P)PNe) we aim to recover, or
constrain, the mass loss history experienced by these stars in their recent
past. The Far-Infrared Surveyor (FIS) instrument on board the AKARI satellite
was used to obtain far-infrared maps for a selected sample of post-AGB stars
and (P)PNe. We derived flux densities (aperture photometry) for 13 post-AGB
stars and (P)PNe at four far-infrared wavelengths (60, 90, 140, and 160 um).
Radial (azimuthally averaged) profiles are used to investigate the presence of
extended emission from cool dust. No (detached) extended emission is detected
for any target in our sample at levels significant with respect to background
and cirrus emission. Only IRAS 21046+4739 reveals tentative excess emission
between 30 and 130". Estimates of the total dust and gas mass from the obtained
maps indicate that the envelope masses of these stars should be large in order
to be detected with the AKARI FIS. Imaging with higher sensitivity and higher
spatial resolution is needed to detect and resolve, if present, any cool
compact or extended emission associated with these evolved stars.Comment: accepted for publication in The Astronomical Journal (16 pages, 3
figures and 4 tables
Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARI
We investigate the structure of the interstellar medium (ISM) and identify
the location of possible embedded excitation sources from far-infrared (FIR)
line and mid-infrared continuum emission maps. We carried out imaging
spectroscopic observations of four giant Galactic star-forming regions with the
Fourier Transform Spectrometer (FTS) onboard AKARI. We obtained [OIII] 88
micron and [CII] 158 micron line intensity maps of all the regions:
G3.270-0.101, G333.6-0.2, NGC3603, and M17. For G3.270-0.101, we obtained
high-spatial-resolution [OIII] 88 micron line-emission maps and a FIR continuum
map for the first time, which imply that [OIII] 88 micron emission identifies
the excitation sources more clearly than the radio continuum emission. In
G333.6-0.2, we found a local [OIII] 88 micron emission peak, which is
indicative of an excitation source. This is supported by the 18 micron
continuum emission, which is considered to trace the hot dust distribution. For
all regions, the [CII] 158 micron emission is distributed widely as suggested
by previous observations of star-forming regions. We conclude that [OIII] 88
micron emission traces the excitation sources more accurately than the radio
continuum emission, especially where there is a high density and/or column
density gradient. The FIR spectroscopy provides a promising means of
understanding the nature of star-forming regions.Comment: 14 pages with 15 figures, accepted for publication in Astronomy and
Astrophysic
Ice: a strongly correlated proton system
We discuss the problem of proton motion in Hydrogen bond materials with
special focus on ice. We show that phenomenological models proposed in the past
for the study of ice can be recast in terms of microscopic models in close
relationship to the ones used to study the physics of Mott-Hubbard insulators.
We discuss the physics of the paramagnetic phase of ice at 1/4 filling (neutral
ice) and its mapping to a transverse field Ising model and also to a gauge
theory in two and three dimensions. We show that H3O+ and HO- ions can be
either in a confined or deconfined phase. We obtain the phase diagram of the
problem as a function of temperature T and proton hopping energy t and find
that there are two phases: an ordered insulating phase which results from an
order-by-disorder mechanism induced by quantum fluctuations, and a disordered
incoherent metallic phase (or plasma). We also discuss the problem of
decoherence in the proton motion introduced by the lattice vibrations (phonons)
and its effect on the phase diagram. Finally, we suggest that the transition
from ice-Ih to ice-XI observed experimentally in doped ice is the
confining-deconfining transition of our phase diagram.Comment: 12 pages, 9 figure
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