381 research outputs found
An AKARI Search for Intracluster Dust of Globular Clusters
We report the observations of 12 globular clusters with the AKARI/FIS. Our
goal is to search for emission from the cold dust within clusters. We detect
diffuse emissions toward NGC 6402 and 2808, but the IRAS 100-micron maps show
the presence of strong background radiation. They are likely emitted from the
galactic cirrus, while we cannot rule out the possible association of a bump of
emission with the cluster in the case of NGC 6402. We also detect 28 point-like
sources mainly in the WIDE-S images (90 micron). At least several of them are
not associated with the clusters but background galaxies based on some external
catalogs. We present the SEDs by combining the near-and-mid infrared data
obtained with the IRC if possible. The SEDs suggest that most of the point
sources are background galaxies. We find one candidate of the intracluster dust
which has no mid-infrared counterpart unlike the other point-like sources,
although some features such as its point-like appearance should be explained
before we conclude its intracluster origin. For most of the other clusters, we
have confirmed the lack of the intracluster dust. We evaluate upper limits of
the intracluster dust mass to be between 1.0E-05 and 1.0E-03 solar mass
depending on the dust temperature. The lifetime of the intracluster dust
inferred from the upper limits is shorter than 5 Myr (T=70K) or 50 Myr (35K).
Such short lifetime indicates some mechanism(s) are at work to remove the
intracluster dust. We also discuss its impact on the chemical evolution of
globular clusters.Comment: Accepted for publication in PASJ AKARI special issue. 14 pages, 11
figure
AKARI Near- to Mid-Infrared Imaging and Spectroscopic Observations of the Small Magellanic Cloud. I. Bright Point Source List
We carried out a near- to mid-infrared imaging and spectroscopic observations
of the patchy areas in the Small Magellanic Cloud using the Infrared Camera on
board AKARI. Two 100 arcmin2 areas were imaged in 3.2, 4.1, 7, 11, 15, and 24
um and also spectroscopically observed in the wavelength range continuously
from 2.5 to 13.4 um. The spectral resolving power (lambda/Delta lambda) is
about 20, 50, and 50 at 3.5, 6.6 and 10.6 um, respectively. Other than the two
100 arcmin2 areas, some patchy areas were imaged and/or spectroscopically
observed as well. In this paper, we overview the observations and present a
list of near- to mid-infrared photometric results, which lists ~ 12,000
near-infrared and ~ 1,800 mid-infrared bright point sources detected in the
observed areas. The 10 sigma limits are 16.50, 16.12, 13.28, 11.26, 9.62, and
8.76 in Vega magnitudes at 3.2, 4.1, 7, 11, 15, and 24 um bands, respectively.Comment: 16 pages, 7 figures, accepted for publication in PASJ. Full
resolution version is available at
http://www-irc.mtk.nao.ac.jp/%7Eyita/smc20100112.pd
FEASIBILITY STUDY ON THE FUSION OF PHITS SIMULATIONS AND THE DLNN ALGORITHM
We have recently have developed an in-situ multiple-channel depth distribution spectrometer (DDS) that can easily acquire on-site measurements of the depth distribution of specific radioactivities of Cs-134 and Cs-137 underground. Despite considerable improvements in the hardware developed for this device, the quantitative method for determining of radioactivities with this DDS device cannot yet achieve satisfactory performance for practical use. For example, this method cannot discriminate each γ-ray spectra of Cs-134 and Cs-137 acquired by the 20 thallium-doped caesium iodine CsI(Tl) scintillation crystal detectors of the DDS device from corresponding depth levels of underground soil. Therefore, we have applied deep learning neural network (DLNN) as a novel radiation measurement technique to discriminate the spectra and to determine the specific radioactivities of Cs-134 and Cs-137. We have developed model soil layers on a virtual space in Monte-Carlo based PHITS simulations and transported γ-ray radiation generated from a particular single soil layer or multiple layers as radiation sources; next, we performed PHITS calculations of those specific radioactivity measurements for each soil layer using DDS device based on machine learning via the DLNN algorithm. In this study, we obtained informative results regarding the feasibility of the proposal innovative radiation measurement method for further practical use in on-site applications
Variation of radiocesium concentrations in cedar pollen in the Okutama area since the Fukushima Daiichi Nuclear Power Plant Accident
Due to releases of radionuclides in the Fukushima Daiichi Nuclear Power Plant Accident, radiocesium (¹³⁴Cs and ¹³⁷Cs) has been incorporated into large varieties of plant species and soil types. There is a possibility that radiocesium taken into plants is being diffused by pollen. Radiocesium concentrations in cedar pollen have been measured in Ome City, located in the Okutama area of metropolitan Tokyo, for the past 3 years. In this research, the variation of radiocesium concentrations was analysed by comparing data from 2011 to 2014. Air dose rates at 1 m above the ground surface in Ome City from 2011 to 2014 showed no significant difference. Concentration of ¹³⁷Cs contained in the cedar pollen in 2012 was about half that in 2011. Between 2012 and 2014, the concentration decreased by approximately one fifth, which was similar to the result of a press release distributed by the Japanese Ministry of Agriculture, Forestry and Fisheries
The interface between the stellar wind and interstellar medium around R Cassiopeiae revealed by far-infrared imaging
The circumstellar dust shells of intermediate initial-mass (about 1 to 8
solar masses) evolved stars are generated by copious mass loss during the
asymptotic giant branch phase. The density structure of their circumstellar
shell is the direct evidence of mass loss processes, from which we can
investigate the nature of mass loss. We used the AKARI Infrared Astronomy
Satellite and the Spitzer Space Telescope to obtain the surface brightness maps
of an evolved star R Cas at far-infrared wavelengths, since the temperature of
dust decreases as the distance from the star increases and one needs to probe
dust at lower temperatures, i.e., at longer wavelengths. The observed shell
structure and the star's known proper motion suggest that the structure
represents the interface regions between the dusty wind and the interstellar
medium. The deconvolved structures are fitted with the analytic bow shock
structure to determine the inclination angle of the bow shock cone. Our data
show that (1) the bow shock cone of 1 - 5 x 10^-5 solar masses (dust mass) is
inclined at 68 degrees with respect to the plane of the sky, and (2) the dust
temperature in the bow shock cone is raised to more than 20 K by collisional
shock interaction in addition to the ambient interstellar radiation field. By
comparison between the apex vector of the bow shock and space motion vector of
the star we infer that there is a flow of interstellar medium local to R Cas
whose flow velocity is at least 55.6 km/s, consistent with an environment
conducive to dust heating by shock interactions.Comment: 7 pages, 2 figures, accepted for publication in Astronomy and
Astrophysic
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