18 research outputs found
Galactic distributions of carbon- and oxygen-rich AGB stars revealed by the AKARI mid-infrared all-sky survey
Context: The environmental conditions for asympotic giant branch (AGB) stars
to reach the carbon-rich (C-rich) phase are important to understand the
evolutionary process of AGB stars. The difference between the spatial
distributions of C-rich and oxygen-rich (O-rich) AGB stars is essential for the
study of the Galactic structure and the chemical evolution of the interstellar
medium (ISM). Aims: We quantitatively investigate the spatial distributions of
C-rich and O-rich AGB stars in our Galaxy. We discuss the difference between
them and its origin. Methods: We classify a large number of AGB stars newly
detected by the AKARI id-infrared all-sky survey. In the color-color diagrams,
we define their occupation zones based on the locations of known objects. We
then obtain the spatial distributions of C-rich and O-rich AGB stars, assuming
that they have the same luminosity for a given mass-loss rate. Results: We find
that O-rich AGB stars are concentrated toward the Galactic center and that the
density decreases with Galactocentric distance, whereas C-rich AGB stars show a
relatively uniform distribution within about 8kpc of Sun. Conclusion: Our
result confirms the trends reported in previous studies and extends them to a
Galactic scale. We discuss the relations between our result, the Galactic
metallicity gradient, and the chemical evolution of the ISM in our Galaxy.Comment: 13 pages, 24 figures, Accepted for A&
Characterization and Improvement of the Image Quality of the Data Taken with the Infrared Camera (IRC) Mid-Infrared Channels onboard AKARI
Mid-infrared images frequently suffer artifacts and extended point spread
functions (PSFs). We investigate the characteristics of the artifacts and the
PSFs in images obtained with the Infrared Camera (IRC) onboard AKARI at four
mid-infrared bands of the S7 (7{\mu}m), S11 (11{\mu}m), L15 (15{\mu}m), and L24
(24 {\mu}m). Removal of the artifacts significantly improves the reliability of
the ref- erence data for flat-fielding at the L15 and L24 bands. A set of
models of the IRC PSFs is also constructed from on-orbit data. These PSFs have
extended components that come from diffraction and scattering within the
detector arrays. We estimate the aperture correction factors for point sources
and the surface brightness correction factors for diffuse sources. We conclude
that the surface brightness correction factors range from 0.95 to 0.8, taking
account of the extended component of the PSFs. To correct for the extended PSF
effects for the study of faint structures, we also develop an image
reconstruction method, which consists of the deconvolution with the PSF and the
convolution with an appropriate Gaussian. The appropriate removal of the
artifacts, improved flat-fielding, and image reconstruction with the extended
PSFs enable us to investigate de- tailed structures of extended sources in IRC
mid-infrared images.Comment: 35 pages, 15 figures, accepted for publication in PAS
AKARI Detection of the Infrared-Bright Supernova Remnant B0104-72.3 in the Small Magellanic Cloud
We present a serendipitous detection of the infrared-bright supernova remnant
(SNR) B0104-72.3 in the Small Magellanic Cloud by the Infrared Camera (IRC)
onboard AKARI. An elongated, partially complete shell is detected in all four
observed IRC bands covering 2.6-15 um. The infrared shell surrounds radio,
optical, and X-ray emission associated with the SNR and is probably a radiative
SNR shell. This is the first detection of a SNR shell in this near/mid-infrared
waveband in the Small Magellanic Cloud. The IRC color indicates that the
infrared emission might be from shocked H2 molecules with some possible
contributions from ionic lines. We conclude that B0104-72.3 is a middle-aged
SNR interacting with molecular clouds, similar to the Galactic SNR IC 443. Our
results highlight the potential of AKARI IRC observations in studying SNRs,
especially for diagnosing SNR shocks.Comment: 12 pages with 3 figures, accepted for publication in AKARI PASJ
special issu
AKARI Near Infrared Spectroscopy: Detection of H2O and CO2 Ices toward Young Stellar Objects in the Large Magellanic Cloud
We present the first results of AKARI Infrared Camera near-infrared spec-
troscopic survey of the Large Magellanic Cloud (LMC). We detected absorption
features of the H2O ice 3.05 um and the CO2 ice 4.27 um stretching mode toward
seven massive young stellar objects (YSOs). These samples are for the first
time spectroscopically confirmed to be YSOs. We used a curve-of-growth method
to evaluate the column densities of the ices and derived the CO2/H2O ratio to
be 0.45 pm 0.17. This is clearly higher than that seen in Galactic massive YSOs
(0.17 pm 0.03). We suggest that the strong ultraviolet radiation field and/or
the high dust temperature in the LMC may be responsible for the observed high
CO2 ice abundance.Comment: 11 pages, 1 table, 2 figure
AKARI infrared imaging of reflection nebulae IC4954 and IC4955
We present the observations of the reflection nebulae IC4954 and IC4955
region with the Infrared Camera (IRC) and the Far-Infrared Surveyor (FIS) on
board the infrared astronomical satellite AKARI during its performance
verification phase. We obtained 7 band images from 7 to 160um with higher
spatial resolution and higher sensitivities than previous observations. The
mid-infrared color of the S9W (9um) and L18W (18um) bands shows a systematic
variation around the exciting sources. The spatial variation in the
mid-infrared color suggests that the star-formation in IC4954/4955 is
progressing from south-west to north-east. The FIS data also clearly resolve
two nebulae for the first time in the far-infrared. The FIS 4-band data from
65um to 160um allow us to correctly estimate the total infrared luminosity from
the region, which is about one sixth of the energy emitted from the existing
stellar sources. Five candidates for young stellar objects have been detected
as point sources for the first time in the 11um image. They are located in the
red S9W to L18W color regions, suggesting that current star-formation has been
triggered by previous star-formation activities. A wide area map of the size of
about 1 x 1 (deg^2) around the IC4954/4955 region was created from the AKARI
mid-infrared all-sky survey data. Together with the HI 21cm data, it suggests a
large hollow structure of a degree scale, on whose edge the IC4954/4955 region
has been created, indicating star formation over three generations in largely
different spatial scales.Comment: 23 pages, 7 figures, accepted for publication in PASJ AKARI special
issu
AKARI IRC survey of the Large Magellanic Cloud: Outline of the survey and initial results
We observed an area of 10 deg^2 of the Large Magellanic Cloud using the
Infrared Camera on board AKARI. The observations were carried out using five
imaging filters (3, 7, 11, 15, and 24 micron) and a dispersion prism (2 -- 5
micron, 20) equipped in the IRC. This paper
describes the outline of our survey project and presents some initial results
using the imaging data that detected over 5.9x10^5 near-infrared and 6.4x10^4
mid-infrared point sources. The 10 detection limits of our survey are
about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3, 7, 11, 15, and 24
micron, respectively. The 11 and 15 micron data, which are unique to AKARI IRC,
allow us to construct color-magnitude diagrams that are useful to identify
stars with circumstellar dust. We found a new sequence in the color-magnitude
diagram, which is attributed to red giants with luminosity fainter than that of
the tip of the first red giant branch. We suggest that this sequence is likely
to be related to the broad emission feature of aluminium oxide at 11.5 micron.
The 11 and 15 micron data also indicate that the ([11] - [15]) micron color of
both oxygen-rich and carbon-rich red giants once becomes blue and then turns
red again in the course of their evolution, probably due to the change in the
flux ratio of the silicate or silicon carbide emission feature at 10 or 11.3
micron to the 15 micron flux.Comment: Accepted for publication in PASJ AKARI special issue. High resolution
version is available at:
http://www-irc.mtk.nao.ac.jp/yita/lmc20080822.ps.gz (8.9MB