548 research outputs found
Diffraction-limited Subaru imaging of M82: sharp mid-infrared view of the starburst core
We present new imaging at 12.81 and 11.7 microns of the central ~40"x30"
(~0.7x0.5 kpc) of the starburst galaxy M82. The observations were carried out
with the COMICS mid-infrared (mid-IR) imager on the 8.2m Subaru telescope, and
are diffraction-limited at an angular resolution of <0".4. The images show
extensive diffuse structures, including a 7"-long linear chimney-like feature
and another resembling the edges of a ruptured bubble. This is the clearest
view to date of the base of the kpc-scale dusty wind known in this galaxy.
These structures do not extrapolate to a single central point, implying
multiple ejection sites for the dust. In general, the distribution of dust
probed in the mid-IR anticorrelates with the locations of massive star clusters
that appear in the near-infrared. The 10-21 micron mid-IR emission,
spatially-integrated over the field of view, may be represented by hot dust
with temperature of ~160 K. Most discrete sources are found to have extended
morphologies. Several radio HII regions are identified for the first time in
the mid-IR. The only potential radio supernova remnant to have a mid-IR
counterpart is a source which has previously also been suggested to be a weak
active galactic nucleus. This source has an X-ray counterpart in Chandra data
which appears prominently above 3 keV and is best described as a hot (~2.6 keV)
absorbed thermal plasma with a 6.7 keV Fe K emission line, in addition to a
weaker and cooler thermal component. The mid-IR detection is consistent with
the presence of strong [NeII]12.81um line emission. The broad-band source
properties are complex, but the X-ray spectra do not support the active
galactic nucleus hypothesis. We discuss possible interpretations regarding the
nature of this source.Comment: Accepted for publication in PASJ Subaru special issue. High
resolution version available temporarily at
http://www.astro.isas.jaxa.jp/~pgandhi/pgandhi_m82.pd
Thermal Properties of Heavy Fermion Compound YbP
Low-temperature specific heat and its field-dependence up to 16 T was
measured in a stoichiometric single crystal of YbP. A sharp peak was observed
at {\it T} = 0.53 K in zero magnetic field. Application of external
field seems to induce a new magnetic phase above 11 T. The field dependence of
the transition temperature in the high-field phase is different from that of
the low field phase. The linear coefficient of the electronic specific heat is
estimated as 120 mJ/mole K from low temperature specfic heat, suggesting
heavy Fermion state in YbP.Comment: to be published in J.Phys.Soc.Jpn on May, 200
Spectroscopic observations of ices around embedded young stellar objects in the Large Magellanic Cloud with AKARI
The aim of this study is to understand the chemical conditions of ices around
embedded young stellar objects (YSOs) in the metal-poor Large Magellanic Cloud
(LMC). We performed near-infrared (2.5-5 micron) spectroscopic observations
toward 12 massive embedded YSOs and their candidates in the LMC using the
Infrared Camera (IRC) onboard AKARI. We estimated the column densities of the
H2O, CO2, and CO ices based on their 3.05, 4.27, and 4.67 micron absorption
features, and we investigated the correlation between ice abundances and
physical properties of YSOs.The ice absorption features of H2O, CO2, 13CO2, CO,
CH3OH, and possibly XCN are detected in the spectra. In addition, hydrogen
recombination lines and PAH emission bands are detected toward the majority of
the targets. The derived typical CO2/H2O ice ratio of our samples (~0.36 +-
0.09) is greater than that of Galactic massive YSOs (~0.17 +- 0.03), while the
CO/H2O ice ratio is comparable. It is shown that the CO2 ice abundance does not
correlate with the observed characteristics of YSOs; the strength of hydrogen
recombination line and the total luminosity. Likewise, clear no correlation is
seen between the CO ice abundance and YSO characteristics, but it is suggested
that the CO ice abundance of luminous samples is significantly lower than in
other samples.The systematic difference in the CO2 ice abundance around the
LMC's massive YSOs, which was suggested by previous studies, is confirmed with
the new near-infrared data. We suggest that the strong ultraviolet radiation
field and/or the high dust temperature in the LMC are responsible for the
observed high abundance of the CO2 ice. It is suggested that the internal
stellar radiation does not play an important role in the evolution of the CO2
ice around a massive YSO, while more volatile molecules like CO are susceptible
to the effect of the stellar radiation.Comment: 12 pages, 8 figures, 5 tables, accepted for Astronomy & Astrophysics
journa
Temperature dependence of ESR intensity for the nanoscale molecular magnet V15
The electron spin resonance (ESR) of nanoscale molecular magnet is studied. Since the Hamiltonian of has a large
Hilbert space and numerical calculations of the ESR signal evaluating the Kubo
formula with exact diagonalization method is difficult, we implement the
formula with the help of the random vector technique and the Chebyshev
polynominal expansion, which we name the double Chebyshev expansion method. We
calculate the temperature dependence of the ESR intensity of and
compare it with the data obtained in experiment. As another complementary
approach, we also implement the Kubo formula with the subspace iteration method
taking only important low-lying states into account. We study the ESR
absorption curve below by means of both methods. We find that side
peaks appear due to the Dzyaloshinsky-Moriya interaction and these peaks grows
as temperature decreases.Comment: 9 pages, 4 figures. To appear in J. Phys. Soc. Jpn. Supp
AKARI observations of ice absorption bands towards edge-on young stellar objects
To investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (YSOs), we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. We performed slit-less spectroscopic observations using the grism mode of the InfraRed Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 mu m to 5 mu m, including the CO2 band and the blue wing of the H2O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element. Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H2O, CO2, CO, and XCN are clearly detected. Column density ratios of CO2 ice and CO ice relative to H2O ice are 21-28% and 13-46%, respectively. If XCN is OCN-, its column density is as high as 2-6% relative to H2O ice. The HDO ice feature at 4.1 mu m is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 mu m provide upper limits to the CH3OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H2O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN-could originate in the region close to the protostar, where there are warm temperatures and UV radiation. We detect H2O ice band towards ASR41 and 2MASSJ 1628137-243139, which are edge-on class II disks. We also detect H2O ice and CO2 ice towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features towards HK Tau and UY Aur
The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
We present a theoretical model for Type Ib supernova (SN) 2006jc. We
calculate the evolution of the progenitor star, hydrodynamics and
nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC).
The synthetic bolometric LC is compared with the observed bolometric LC
constructed by integrating the UV, optical, near-infrared (NIR), and
mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as
on the zero-age main-sequence. The star undergoes extensive mass
loss to reduce its mass down to as small as , thus becoming a WCO
Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which
amorphous carbon grains can be formed. This could explain the NIR brightening
and the dust feature seen in the MIR spectrum. We suggest that the progenitor
of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and
such massive stars are the important sites of dust formation. We derive the
parameters of the explosion model in order to reproduce the bolometric LC of SN
2006jc by the radioactive decays: the ejecta mass , hypernova-like
explosion energy ergs, and ejected Ni mass . We
also calculate the circumstellar interaction and find that a CSM with a flat
density structure is required to reproduce the X-ray LC of SN 2006jc. This
suggests a drastic change of the mass-loss rate and/or the wind velocity that
is consistent with the past luminous blue variable (LBV)-like event.Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
Si and Fe depletion in Galactic star-forming regions observed by the Spitzer Space Telescope
We report the results of the mid-infrared spectroscopy of 14 Galactic
star-forming regions with the high-resolution modules of the Infrared
Spectrograph (IRS) on board the Spitzer Space Telescope. We detected [SiII]
35um, [FeII] 26um, and [FeIII] 23um as well as [SIII] 33um and H2 S(0) 28um
emission lines. Using the intensity of [NII] 122um or 205um and [OI] 146um or
63um reported by previous observations in four regions, we derived the ionic
abundance Si+/N+ and Fe+/N+ in the ionized gas and Si+/O0 and Fe+/O0 in the
photodissociation gas. For all the targets, we derived the ionic abundance of
Si+/S2+ and Fe2+/S2+ for the ionized gas. Based on photodissociation and HII
region models the gas-phase Si and Fe abundance are suggested to be 3-100% and
<8% of the solar abundance, respectively, for the ionized gas and 16-100% and
2-22% of the solar abundance, respectively, for the photodissociation region
gas. Since the [FeII] 26um and [FeIII] 23um emissions are weak, the high
sensitivity of the IRS enables to derive the gas-phase Fe abundance widely in
star-forming regions. The derived gas-phase Si abundance is much larger than
that in cool interstellar clouds and that of Fe. The present study indicates
that 3-100% of Si atoms and <22% of Fe atoms are included in dust grains which
are destroyed easily in HII regions, probably by the UV radiation. We discuss
possible mechanisms to account for the observed trend; mantles which are
photodesorbed by UV photons, organometallic complexes, or small grains.Comment: 43 pages with 7 figures, accepted in Astrophysical Journa
AKARI observations of ice absorption bands towards edge-on YSOs
To investigate the composition and evolution of circumstellar ice around
low-mass YSOs, we observed ice absorption bands in the near infrared (NIR)
towards eight YSOs ranging from class 0 to class II, among which seven are
associated with edge-on disks. We performed slit-less spectroscopic
observations using the grism mode of the Infrared Camera (IRC) on board AKARI,
which enables us to obtain full NIR spectra from 2.5 m to 5 m. The
spectra were fitted with polynomial baselines to derive the absorption spectra.
The molecular absorption bands were then fitted with the laboratory database of
ice absorption bands, considering the instrumental line profile and the
spectral resolution of the grism dispersion element. Towards the class 0-I
sources (L1527, IRC-L1041-2, and IRAS04302), absorption bands of HO,
CO, CO, and XCN are clearly detected. Column density ratios of CO ice
and CO ice relative to HO ice are 21-28% and 13-46%, respectively. If XCN
is OCN, its column density is as high as 2-6% relative to HO ice. The
HDO ice feature at 4.1 m is tentatively detected towards the class 0-I
sources and HV Tau. Non-detections of the CH-stretching mode features around
3.5 m provide upper limits to the CHOH abundance of 26% (L1527) and
42% (IRAS04302) relative to HO. We tentatively detect OCS ice absorption
towards IRC-L1041-2. Towards class 0-I sources, the detected features should
mostly originate in the cold envelope, while CO gas and OCN could originate
in the region close to the protostar, where there are warm temperatures and UV
radiation. We detect HO ice band towards ASR41 and 2MASSJ1628137-243139,
which are edge-on class II disks. We also detect HO ice and CO ice
towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features
towards HK Tau and UY Aur.Comment: Accepted to A&
A comprehensive evaluation of colonic mucosal isolates of Sutterella wadsworthensis from inflammatory bowel disease
Peer reviewedPublisher PD
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