386 research outputs found
Flared Disks and Silicate Emission in Young Brown Dwarfs
We present mid-infrared photometry of three very young brown dwarfs located
in the Ophiuchi star-forming region -- GY5, GY11 and GY310 --obtained
with the Subaru 8-meter telescope. All three sources were detected at 8.6 and
11.7m, confirming the presence of significant mid-infrared excess arising
from optically thick dusty disks. The spectral energy distributions of both
GY310 and GY11 exhibit strong evidence of flared disks; flat disks can be ruled
out for these two brown dwarfs. The data for GY5 show large scatter, and are
marginally consistent with both flared and flat configurations. Inner holes a
few substellar radii in size are indicated in all three cases (and especially
in GY11), in agreement with magnetospheric accretion models. Finally, our
9.7m flux for GY310 implies silicate emission from small grains on the
disk surface (though the data do not completely preclude larger grains with no
silicate feature). Our results demonstrate that disks around young substellar
objects are analogous to those girdling classical T Tauri stars, and exhibit a
similar range of disk geometries and dust properties.Comment: submitted to Astrophysical Journal Letter
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&
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
Kilonova from post-merger ejecta as an optical and near-Infrared counterpart of GW170817
Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for >10âd is explained by 0.03âMâ of ejecta containing lanthanide elements. However, the blue optical component observed at the initial phases requires an ejecta component with a relatively high electron fraction (Ye). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejecta with a medium Ye of âŒ0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejection after the first dynamical ejection is quite efficient. Our results indicate that NS mergers synthesize a wide range of r-process elements and strengthen the hypothesis that NS mergers are the origin of r-process elements in the Universe
A red supergiant nebula at 25 micron: arcsecond scale mass-loss asymmetries of mu Cep
We present diffraction limited (0.6") 24.5micron Subaru/COMICS images of the
red supergiant mu Cep. We report the detection of a circumstellar nebula, that
was not detected at shorter wavelengths. It extends to a radius of at least 6"
in the thermal infrared. On these angular scales, the nebula is roughly
spherical, in contrast, it displays a pronounced asymmetric morphology closer
in. We simultaneously model the azimuthally averaged intensity profile of the
nebula and the observed spectral energy distribution using spherical dust
radiative transfer models. The models indicate a constant mass-loss process
over the past 1000 years, for mass-loss rates a few times 10^(-7) Msun/yr. This
work supports the idea that at least part of the asymmetries in shells of
evolved massive stars and supernovae may be due to the mass-loss process in the
red supergiant phase.Comment: Accepted for publication in ApJ Letter
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&
Functionalized boron nitride membranes with ultrafast solvent transport performance for molecular separation
Pressure-driven, superfast organic solvent filtration membranes have significant practical applications. An excellent filtration membrane should exhibit high selectivity and permeation in aqueous and organic solvents to meet increasing industrial demand. Here, we report an amino functionalized boron nitride (FBN) based filtration membrane with a nanochannel network for molecular separation and permeation. This membrane is highly stable in water and in several organic solvents and shows high transport performance for solvents depending on the membranes' thickness. In addition, the FBN membrane is applicable for solute screening in water as well as in organic solvents. More importantly, the FBN membranes are very stable in acidic, alkaline and oxidative media for up to one month. The fast-flow rate and good separation performance of the FBN membranes can be attributed to their stable networks of nanochannels and thin laminar structure, which provide the membranes with beneficial properties for practical separation and purification processes
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