398 research outputs found
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
Resolved 24.5 micron emission from massive young stellar objects
Massive young stellar objects (MYSO) are surrounded by massive dusty
envelopes. Our aim is to establish their density structure on scales of ~1000
AU, i.e. a factor 10 increase in angular resolution compared to similar studies
performed in the (sub)mm. We have obtained diffraction-limited (0.6") 24.5
micron images of 14 well-known massive star formation regions with
Subaru/COMICS. The images reveal the presence of discrete MYSO sources which
are resolved on arcsecond scales. For many sources, radiative transfer models
are capable of satisfactorily reproducing the observations. They are described
by density powerlaw distributions (n(r) ~ r^(-p)) with p = 1.0 +/-0.25. Such
distributions are shallower than those found on larger scales probed with
single-dish (sub)mm studies. Other sources have density laws that are
shallower/steeper than p = 1.0 and there is evidence that these MYSOs are
viewed near edge-on or near face-on, respectively. The images also reveal a
diffuse component tracing somewhat larger scale structures, particularly
visible in the regions S140, AFGL 2136, IRAS 20126+4104, Mon R2, and Cep A. We
thus find a flattening of the MYSO envelope density law going from ~10 000 AU
down to scales of ~1000 AU. We propose that this may be evidence of rotational
support of the envelope (abridged).Comment: 21 pages, accepted for A&
Crystalline Silicate Feature of the Vega-like star HD145263
We have observed the 8-13 m spectrum (R250) of the Vega-like star
candidate HD145263 using Subaru/COMICS. The spectrum of HD145263 shows the
broad trapezoidal silicate feature with the shoulders at 9.3 m and 11.44
m, indicating the presence of crystalline silicate grains. This detection
implies that crystalline silicate may also be commonly present around Vega-like
stars. The 11.44 m feature is slightly shifted to a longer wavelength
compared to the usual 11.2-3 m crystalline forsterite feature detected
toward Herbig Ae/Be stars and T Tauri stars. Although the peak shift due to the
effects of the grain size can not be ruled out, we suggest that Fe-bearing
crystalline olivine explains the observed peak wavelength fairly well.
Fe-bearing silicates are commonly found in meteorites and most interplanetary
dust particles, which originate from planetesimal-like asteroids. According to
studies of meteorites, Fe-bearing silicate must have been formed in asteroidal
planetesimals, supporting the scenario that dust grains around Vega-like stars
are of planetesimal origin, if the observed 11.44 m peak is due to
Fe-bearing silicates.Comment: accepted for Publication in ApJ
Ectopic cardiovascular fat in middle-aged men: effects of race/ethnicity, overall and central adiposity. The ERA JUMP study.
Background/objectivesHigher volumes of ectopic cardiovascular fat (ECF) are associated with greater risk of coronary heart disease (CHD). Identifying factors that are associated with ECF volumes may lead to new preventive efforts to reduce risk of CHD. Significant racial/ethnic differences exist for overall and central adiposity measures, which are known to be associated with ECF volumes. Whether racial/ethnic differences also exist for ECF volumes and their associations with these adiposity measures remain unclear.Subjects/methodsBody mass index (BMI), computerized tomography-measured ECF volumes (epicardial, pericardial and their summation) and visceral adipose tissue (VAT) were examined in a community-based sample of 1199 middle-aged men (24.2% Caucasians, 7.0% African-Americans, 23.6% Japanese-Americans, 22.0% Japanese, 23.2% Koreans).ResultsSignificant racial/ethnic differences existed in ECF volumes and their relationships with BMI and VAT. ECF volumes were the highest among Japanese-Americans and the lowest among African-Americans. The associations of BMI and VAT with ECF differed by racial/ethnic groups. Compared with Caucasians, for each 1-unit increase in BMI, African-Americans had lower, whereas Koreans had higher increases in ECF volumes (P-values<0.05 for both). Meanwhile, compared with Caucasians, for each 1-unit increase in log-transformed VAT, African-Americans, Japanese-Americans and Japanese had similar increases, whereas Koreans had a lower increase in ECF volumes (P-value<0.05).ConclusionsRacial/ethnic groups differed in their propensity to accumulate ECF at increasing level of overall and central adiposity. Future studies should evaluate whether reducing central adiposity or overall weight will decrease ECF volumes more in certain racial/ethnic groups. Evaluating these questions might help in designing race-specific prevention strategy of CHD risk associated with higher ECF
Direct detection of a flared disk around a young massive star HD200775 and its 10 to 1000AU scale properties
We made mid-infrared observations of the 10Msun Herbig Be star HD200775 with
the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2m Subaru
Telescope. We discovered diffuse emission of an elliptical shape extended in
the north-south direction inabout 1000AU radius around unresolved excess
emission. The diffuse emission is perpendicular to the cavity wall formed by
the past outflow activity and is parallel to the projected major axis of the
central close binary orbit. The centers of the ellipse contours of the diffuse
emission are shifted from the stellar position and the amount of the shift
increases as the contour brightness level decreases. The diffuse emission is
well explained in all of geometry, size, and configuration by an inclined
flared disk where only its surface emits the mid-infrared photons. Our results
give the first well-resolved infrared disk images around a massive star and
strongly support that HD200775 is formed through the disk accretion. The disk
survives the main accretion phase and shows a structure similar to that around
lower-mass stars with 'disk atmosphere'. At the same time, the disk also shows
properties characteristic to massive stars such as photoevaporation traced by
the 3.4mm free-free emission and unusual silicate emission with a peak at
9.2micron, which is shorter than that of many astronomical objects. It provides
a good place to compare the disk properties between massive and lower-mass
stars.Comment: 18 pages, 8 figures, accepted by The Astrophysical Journa
Probing the envelopes of massive young stellar objects with diffraction limited mid-infrared imaging
Massive stars form whilst they are still embedded in dense envelopes. As a
result, the roles of rotation, mass loss and accretion in massive star
formation are not well understood. This study evaluates the source of the
Q-band, lambda=19.5 microns, emission of massive young stellar objects (MYSOs).
This allows us to determine the relative importance of rotation and outflow
activity in shaping the circumstellar environments of MYSOs on 1000 AU scales.
We obtained diffraction limited mid-infrared images of a sample of 20 MYSOs
using the VLT/VISIR and Subaru/COMICS instruments. For these 8 m class
telescopes and the sample selected, the diffraction limit, ~0.6", corresponds
to approximately 1000 AU. We compare the images and the spectral energy
distributions (SEDs) observed to a 2D, axis-symmetric dust radiative transfer
model that reproduces VLTI/MIDI observations of the MYSO W33A. We vary the
inclination, mass infall rate, and outflow opening angle to simultaneously
recreate the behaviour of the sample of MYSOs in the spatial and spectral
domains. The mid-IR emission of 70 percent of the MYSOs is spatially resolved.
In the majority of cases, the spatial extent of their emission and their SEDs
can be reproduced by the W33A model featuring an in-falling, rotating dusty
envelope with outflow cavities. There is independent evidence that most of the
sources which are not fit by the model are associated with ultracompact HII
regions and are thus more evolved. We find that, in general, the diverse 20
micron morphology of MYSOs can be attributed to warm dust in the walls of
outflow cavities seen at different inclinations. This implies that the warm
dust in the outflow cavity walls dominates the Q-band emission of MYSOs. In
turn, this emphasises that outflows are an ubiquitous feature of massive star
formation.Comment: Accepted for publication in A&A. The images in this version have been
compressed. A high resolution version is available on reques
Mid-IR imaging of the transitional disk of HD169142: Measuring the size of the gap
The disk around the Herbig Ae star HD\,169142 was imaged and resolved at 18.8
and 24.5\,m using Subaru/COMICS. We interpret the observations using a 2D
radiative transfer model and find evidence for the presence of a large gap. The
MIR images trace dust that emits at the onset of the strong rise in the
spectral energy distribution (SED) at 20\,m, therefore are very sensitive
to the location and characteristics of the inner wall of the outer disk and its
dust. We determine the location of the wall to be 23\,AU from the
star. An extra component of hot dust must exist close to the star. We find that
a hydrostatic optically thick inner disk does not produce enough flux in the
NIR and an optically thin geometrically thick component is our solution to fit
the SED. Considering the recent findings of gaps and holes in a number of
Herbig Ae/Be group I disks, we suggest that such disk structures may be common
in group I sources. Classification as group I should be considered a support
for classification as a transitional disk, though improved imaging surveys are
needed to support this speculation.Comment: 18 pages, 5 figures, accepted to Ap
- …