2,300 research outputs found
Radiative Transfer Modeling of Three-Dimensional Clumpy AGN Tori and its Application to NGC 1068
Recent observations of NGC 1068 and other AGN support the idea of a
geometrically and optically thick dust torus surrounding the central
supermassive black hole and accretion disk of AGN. In type 2 AGN, the torus is
seen roughly edge-on, leading to obscuration of the central radiation source
and a silicate absorption feature near 10 micron. While most of the current
torus models distribute the dust smoothly, there is growing evidence that the
dust must be arranged in clouds. We describe a new method for modeling near-
and mid-infrared emission of 3-dimensional clumpy tori using Monte Carlo
simulations. We calculate the radiation fields of individual clouds at various
distances from the AGN and distribute these clouds within the torus region. The
properties of the individual clouds and their distribution within the torus are
determined from a theoretical approach of self-gravitating clouds close to the
shear limit in a gravitational potential. We demonstrate that clumpiness in AGN
tori can overcome the problem of over-pronounced silicate features. Finally, we
present model calculations for the prototypical Seyfert 2 galaxy NGC 1068 and
compare them to recent high-resolution measurements. Our model is able to
reproduce both the SED and the interferometric observations of NGC 1068 in the
near- and mid-infrared.Comment: 16 pages, 16 figures, 6 tables (figures reduced due to astro-ph
limitations); accepted by A&
Spatially resolved H_2 emission from a very low-mass star
Molecular outflows from very low-mass stars (VLMSs) and brown dwarfs have
been studied very little. So far, only a few CO outflows have been observed,
allowing us to map the immediate circumstellar environment. We present the
first spatially resolved H2 emission around IRS54 (YLW52), a ~0.1-0.2 Msun
Class I source. By means of VLT SINFONI K-band observations, we probed the H2
emission down to the first ~50 AU from the source. The molecular emission shows
a complex structure delineating a large outflow cavity and an asymmetric
molecular jet. Thanks to the detection of several H2 transitions, we are able
to estimate average values along the jet-like structure (from source position
to knot D) of Av~28 mag, T~2000-3000 K, and H2 column density N(H2)~1.7x10^17
cm^-2. This allows us to estimate a mass loss rate of ~2x10^-10 Msun/yr for the
warm H2 component . In addition, from the total flux of the Br Gamma line, we
infer an accretion luminosity and mass accretion rate of 0.64 Lsun and ~3x10^-7
Msun/yr, respectively. The outflow structure is similar to those found in
low-mass Class I and CTTS. However, the Lacc/Lbol ratio is very high (~80%),
and the mass accretion rate is about one order of magnitude higher when
compared to objects of roughly the same mass, pointing to the young nature of
the investigated source.Comment: accepted as a Letter in A&
Embedded AGN and star formation in the central 80 pc of IC 3639
[Abridged] Methods: We use interferometric observations in the -band with
VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear
infrared emission is determined from: 1) the comparison of the correlated
fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution
(VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios,
the IR continuum emission, IR bands produced by polycyclic aromatic
hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral
energy distribution. Results: The unresolved flux of IC 3639 is at , measured with three different baselines in
VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; -), making this the
faintest measurement so far achieved with mid-IR interferometry. The correlated
flux is a factor of - times fainter than the VLT/VISIR total flux
measurement. The observations suggest that most of the mid-IR emission has its
origin on spatial scales between and (-). A composite scenario where the star formation component dominates
over the AGN is favoured by the diagnostics based on ratios of IR
fine-structure emission lines, the shape of the IR continuum, and the PAH and
silicate bands. Conclusions: A composite AGN-starburst scenario is able to
explain both the mid-IR brightness distribution and the IR spectral properties
observed in the nucleus of IC 3639. The nuclear starburst would dominate the
mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]) with a net contribution of . The AGN accounts for the
remaining of the mid-IR flux, ascribed to the unresolved component
in the MIDI observations, and the ionisation of high-excitation lines (e.g.
[NeV] and [OIV]).Comment: Accepted for publication in A&
Diagnostic peritoneal lavage: a review of indications, technique, and interpretation
Diagnostic peritoneal lavage (DPL) is a highly accurate test for evaluating intraperitoneal hemorrhage or a ruptured hollow viscus, but is performed less frequently today due to the increased use of focused abdominal sonography for trauma (FAST) and helical computed tomography (CT). All three of these exams have advantages and disadvantages and thus each still play unique roles in the evaluation of abdominal trauma. Since DPL is performed less frequently today, a review of its indications, technique, and interpretation is pertinent
The dusty torus in the Circinus galaxy: a dense disk and the torus funnel
(Abridged) With infrared interferometry it is possible to resolve the nuclear
dust distributions that are commonly associated with the dusty torus in active
galactic nuclei (AGN). The Circinus galaxy hosts the closest Seyfert 2 nucleus
and previous interferometric observations have shown that its nuclear dust
emission is well resolved.
To better constrain the dust morphology in this active nucleus, extensive new
observations were carried out with MIDI at the Very Large Telescope
Interferometer.
The emission is distributed in two distinct components: a disk-like emission
component with a size of ~ 0.2 1.1 pc and an extended component with a
size of ~ 0.8 1.9 pc. The disk-like component is elongated along PA ~
46{\deg} and oriented perpendicular to the ionisation cone and outflow. The
extended component is elongated along PA ~ 107{\deg}, roughly perpendicular to
the disk component and thus in polar direction. It is interpreted as emission
from the inner funnel of an extended dust distribution and shows a strong
increase in the extinction towards the south-east. We find no evidence of an
increase in the temperature of the dust towards the centre. From this we infer
that most of the near-infrared emission probably comes from parsec scales as
well. We further argue that the disk component alone is not sufficient to
provide the necessary obscuration and collimation of the ionising radiation and
outflow. The material responsible for this must instead be located on scales of
~ 1 pc, surrounding the disk.
The clear separation of the dust emission into a disk-like emitter and a
polar elongated source will require an adaptation of our current understanding
of the dust emission in AGN. The lack of any evidence of an increase in the
dust temperature towards the centre poses a challenge for the picture of a
centrally heated dust distribution.Comment: 30 pages, 12 figures; A&A in pres
Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
The nearby high-mass star binary system Theta 1 Orionis C is the brightest
and most massive of the Trapezium OB stars at the core of the Orion Nebula
Cluster, and it represents a perfect laboratory to determine the fundamental
parameters of young hot stars and to constrain the distance of the Orion
Trapezium Cluster. Between January 2007 and March 2008, we observed T1OriC with
VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well
as with bispectrum speckle interferometry with the ESO 3.6m and the BTA 6m
telescopes (B'- and V'-band). Combining AMBER data taken with three different
3-telescope array configurations, we reconstructed the first VLTI/AMBER
closure-phase aperture synthesis image, showing the T1OriC system with a
resolution of approx. 2 mas. To extract the astrometric data from our
spectrally dispersed AMBER data, we employed a new algorithm, which fits the
wavelength-differential visibility and closure phase modulations along the H-
and K-band and is insensitive to calibration errors induced, for instance, by
changing atmospheric conditions. Our new astrometric measurements show that the
companion has nearly completed one orbital revolution since its discovery in
1997. The derived orbital elements imply a short-period (P=11.3 yrs) and
high-eccentricity orbit (e=0.6) with periastron passage around 2002.6. The new
orbit is consistent with recently published radial velocity measurements, from
which we can also derive the first direct constraints on the mass ratio of the
binary components. We employ various methods to derive the system mass
(M_system=44+/-7 M_sun) and the dynamical distance (d=410+/-20 pc), which is in
remarkably good agreement with recently published trigonometric parallax
measurements obtained with radio interferometry.Comment: 15 pages, 15 figures, accepted by A&
The inner circumstellar disk of the UX Ori star V1026 Sco
The UX Ori type variables (named after the prototype of their class) are
intermediate-mass pre-main sequence objects. One of the most likely causes of
their variability is the obscuration of the central star by orbiting dust
clouds. We investigate the structure of the circumstellar environment of the
UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is
large enough to explain the UX Ori variability. We observed the object in the
low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument
and derived H- and K-band visibilities and closure phases. We modeled our AMBER
observations, published Keck Interferometer observations, archival MIDI/VLTI
visibilities, and the spectral energy distribution using geometric and
temperature-gradient models. Employing a geometric inclined-ring disk model, we
find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the
K band. The best-fit temperature-gradient model consists of a star and two
concentric, ring-shaped disks. The inner disk has a temperature of
1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23
+- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner
temperature of 334^{+35}_{-17} K. The derived inclination of
48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with
the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band).
The position angle of the fitted geometric and temperature-gradient models are
163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg,
respectively. The narrow width of the inner ring-shaped model disk and the disk
gap might be an indication for a puffed-up inner rim shadowing outer parts of
the disk. The intermediate inclination of ~50deg is consistent with models of
UX Ori objects where dust clouds in the inclined disk obscure the central star
AMBER/VLTI observations of the B[e] star MWC 300
Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and
binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC
300 with the VLTI/AMBER instrument in the H and K bands and compared these
observations with temperature-gradient models to derive model parameters.
Results. The measured low visibility values, wavelength dependence of the
visibilities, and wavelength dependence of the closure phase directly suggest
that MWC 300 consists of a resolved disk and a close binary. We present a model
consisting of a binary and a temperature-gradient disk that is able to
reproduce the visibilities, closure phases, and spectral energy distribution.
This model allows us to constrain the projected binary separation (~4.4 mas or
~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature
power-law index, and other parameters.Comment: 4 pages, 1 figure, accepted by A&
- …