318 research outputs found
Interferometer predictions with triangulated images: solving the multi-scale problem
Interferometers play an increasingly important role for spatially resolved
observations. If employed at full potential, interferometry can probe an
enormous dynamic range in spatial scale. Interpretation of the observed
visibilities requires the numerical compu- tation of Fourier integrals over the
synthetic model images. To get the correct values of these integrals, the model
images must have the right size and resolution. Insufficient care in these
choices can lead to wrong results. We present a new general-purpose scheme for
the computation of visibilities of radiative transfer images. Our method
requires a model image that is a list of intensities at arbitrarily placed
positions on the image-plane. It creates a triangulated grid from these
vertices, and assumes that the intensity inside each triangle of the grid is a
linear function. The Fourier integral over each triangle is then evaluated with
an analytic expression and the complex visibility of the entire image is then
the sum of all triangles. The result is a robust Fourier trans- form that does
not suffer from aliasing effects due to grid regularities. The method
automatically ensures that all structure contained in the model gets reflected
in the Fourier transform.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
FU Orionis-type objects are young, low-mass stars with large outbursts in
visible light that last for several years or decades. They are thought to
represent an evolutionary phase during the life of every young star when
accretion from the circumstellar disk is enhanced during recurring time
periods. These outbursts are able to rapidly build up the star while affecting
the circumstellar disk and thus the ongoing or future planet formation. In many
models infall from a circumstellar envelope seems to be necessary to trigger
the outbursts. We observed the J=10 rotational transition of CO and
CO towards eight northern FU Orionis-type stars (V1057 Cyg, V1515 Cyg,
V2492 Cyg, V2493 Cyg, V1735 Cyg, V733 Cep, RNO 1B and RNO 1C) and derive
temperatures and envelope masses and discuss the morphology and kinematics of
the circumstellar material. We detected extended CO emission associated with
all our targets. Smaller scale CO clumps were found to be associated with five
objects with radii of 20005000 AU and masses of 0.020.5 ;
these are clearly heated by the central stars. Three of these envelopes are
also strongly detected in the 2.7 mm continuum. No central CO clumps were
detected around V733 Cep and V710 Cas but there are many other clumps in their
environments. Traces of outflow activity were observed towards V1735 Cyg, V733
Cep and V710 Cas. The diversity of the observed envelopes enables us to set up
an evolutionary sequence between the objects. We find their evolutionary state
to range from early, embedded Class I stage to late, Class II-type objects with
very low-mass circumstellar material. The results reinforce the idea of FU
Orionis-type stars as representatives of a transitory stage between embedded
Class I young stellar objects and classical T-Tauri stars.Comment: 17 pages, 11 figures; accepted for publication in A&
Effect of the 3D distribution on water observations made with the SWI: I. Ganymede
Context. Characterising and understanding the atmospheres of Jovian icy moons is one of the key exploration goals of the Submillimetre Wave Instrument (SWI), which is to be flown on ESA\u27s Jupiter Icy Moons Explorer (JUICE) mission.Aims. The aim of this paper is to investigate how and under which conditions a 3D asymmetric distribution of the atmosphere may affect the SWI observations. In this work we target the role of phase angle for both nadir and limb geometries for unresolved and partially resolved disc observations from large distances.Methods. We adapted the LIME software package, a 3D non-local thermodynamical equilibrium radiative transfer model, to evaluate ortho-H2O populations and synthesise the simulated SWI beam spectra for different study cases of Ganymede\u27s atmosphere. The temperature and density vertical distributions were adopted from a previous work. The study cases presented here were selected according to the distance and operational scenarios of moon monitoring anticipated for SWI during the Jupiter phase of the JUICE mission.Results. We demonstrate that nadir and limb observations at different phase angles will modify the line amplitude and width. Unresolved observations where both absorption against surface continuum and limb emission contributes within the beam will lead to characteristic line wing emission, which may also appear in pure nadir geometry for specific phase angles. We also find that for Ganymede, the 3D non-local thermodynamical equilibrium populations are more highly excited in the upper atmosphere near the sub-solar region than they are in 1D spherically symmetric models. Finally, the 3D radiative transfer is better suited to properly simulate spectral lines for cases where density or population gradients exist along the line of sight
Chemistry of a newly detected circumbinary disk in Ophiuchus
(Abridged) Astronomers recently started discovering exoplanets around binary
systems. Therefore, understanding the formation and evolution of circumbinary
disks is crucial for a complete scenario of planet formation. The aim of this
paper is to present the detection of a circumbinary disk around Oph-IRS67 and
analyse its structure. We present high-angular-resolution (0.4", 60 AU)
observations of C17O, H13CO+ , C34S, SO2, C2H and c-C3H2 molecular transitions
with ALMA at 0.8 mm. The spectrally and spatially resolved maps reveal the
kinematics of the circumbinary disk as well as its chemistry. Molecular
abundances are estimated using RADEX. The continuum emission reveals the
presence of a circumbinary disk around the two sources. This disk has a
diameter of ~620 AU and is well traced by C17O and H13CO+ emission. C2H and
c-C3H2 trace a higher-density region which is spatially offset from the sources
(~430 AU). Finally, SO2 shows compact emission around one of the sources,
Oph-IRS67 B. The molecular transitions which trace the circumbinary disk are
consistent with a Keplerian profile on disk scales (< 200 AU) and an infalling
profile for envelope scales (> 200 AU). The Keplerian fit leads to a mass of
2.2 Msun. Inferred CO abundances w.r.t. H2 are comparable to the canonical ISM
value of 2.7e-4. This study proves the first detection of the circumbinary disk
associated with Oph-IRS67. The disk is chemically differentiated from the
nearby high-density region. The lack of methanol emission suggests the extended
disk dominates the mass budget in the inner- most regions of the protostellar
envelope, generating a flat density profile where less material is exposed to
high temperatures. Thus, complex organic molecules would be associated with
lower column densities. Finally, Oph-IRS67 is a promising candidate for the
detection of both circumstellar disks with higher-angular-resolution
observations.Comment: 19 pages, 14 figures, 6 table
Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry
Outflows driven by large-scale magnetic fields likely play an important role
in the evolution and dispersal of protoplanetary disks, and in setting the
conditions for planet formation. We extend our 2-D axisymmetric non-ideal MHD
model of these outflows by incorporating radiative transfer and simplified
thermochemistry, with the twin aims of exploring how heating influences wind
launching, and illustrating how such models can be tested through observations
of diagnostic spectral lines. Our model disks launch magnetocentrifugal
outflows primarily through magnetic tension forces, so the mass-loss rate
increases only moderately when thermochemical effects are switched on. For
typical field strengths, thermochemical and irradiation heating are more
important than magnetic dissipation. We furthermore find that the entrained
vertical magnetic flux diffuses out of the disk on secular timescales as a
result of non-ideal MHD. Through post-processing line radiative transfer, we
demonstrate that spectral line intensities and moment-1 maps of atomic oxygen,
the HCN molecule, and other species show potentially observable differences
between a model with a magnetically driven outflow and one with a weaker,
photoevaporative outflow. In particular, the line shapes and velocity
asymmetries in the moment-1 maps could enable the identification of outflows
emanating from the disk surface.Comment: 35 pages, 20 figures, accepted for publication in Ap
A deeply embedded young protoplanetary disk around L1489 IRS observed by the submillimeter array
Circumstellar disks are expected to form early in the process that leads to
the formation of a young star, during the collapse of the dense molecular cloud
core. It is currently not well understood at what stage of the collapse the
disk is formed or how it subsequently evolves. We aim to identify whether an
embedded Keplerian protoplanetary disk resides in the L1489 IRS system. Given
the amount of envelope material still present, such a disk would respresent a
very young example of a protoplanetary disk. Using the Submillimeter Array
(SMA) we have observed the HCO 3--2 line with a resolution of about
1. At this resolution a protoplanetary disk with a radius of a few hundred
AUs should be detectable, if present. Radiative transfer tools are used to
model the emission from both continuum and line data. We find that these data
are consistent with theoretical models of a collapsing envelope and Keplerian
circumstellar disk. Models reproducing both the SED and the interferometric
continuum observations reveal that the disk is inclined by 40 which is
significantly different to the surrounding envelope (74). This
misalignment of the angular momentum axes may be caused by a gradient within
the angular momentum in the parental cloud or if L1489 IRS is a binary system
rather than just a single star. In the latter case, future observations looking
for variability at sub-arcsecond scales may be able to constrain these
dynamical variations directly. However, if stars form from turbulent cores, the
accreting material will not have a constant angular momentum axis (although the
average is well defined and conserved) in which case it is more likely to have
a misalignment of the angular momentum axes of the disk and the envelope.Comment: 11 pages, 13 figures, accepted by A&
P and Ca digestibility is increased in broiler diets supplemented with the high-phytase HIGHPHY wheat
Around 70% of total seed phosphorus is represented by phytate which must be hydrolysed to be bioavailable in non-ruminant diets. The limited endogenous phytase activity in non-ruminant animals make it common practice to add an exogenous phytase source to most poultry and pig feeds. The mature grain phytase activity (MGPA) of cereal seeds provides a route for the seeds themselves to contribute to phytate digestion, but MGPA varies considerably between species and most varieties in current use make negligible contributions. Currently, all phytases used for feed supplementation and transgenic improvement of MGPA are derived from microbial enzymes belonging to the group of histidine acid phosphatases (HAP). Cereals contain HAP phytases, but the bulk of MGPA can be attributed to phytases belonging to a completely different group of phosphatases, the purple acid phosphatases (PAPhy). In recent years, increased MGPAs were achieved in cisgenic barley holding extra copies of barley PAPhy and in the wheat HIGHPHY mutant, where MGPA was increased to ~6200 FTU/kg. In the present study, the effect of replacing 33%, 66% and 100% of a standard wheat with HIGHPHY wheat was compared with a control diet with and without 500 FTU of supplemental phytase. Diets were compared by evaluating broiler performance, ileal Ca and P digestibility and tibia development, using nine replicate pens of four birds per diet over 3 weeks from hatch. There were no differences between treatments in any tibia or bird performance parameters, indicating the control diet did not contain sufficiently low levels of phosphorus to distinguish effect of phytase addition. However, in a comparison of the two wheats, the ileal Ca and P digestibility coefficients for the 100% HIGHPHY wheat diets are 22.9% and 35.6% higher, respectively, than for the control diet, indicating the wheat PAPhy is functional in the broiler digestive tract. Furthermore, 33% HIGHPHY replacement of conventional wheat, significantly improved Ca and P digestibility over the diet-supplemented exogenous phytase, probably due to the higher phytase activity in the HIGHPHY diet (1804 v. 1150 FTU). Full replacement by HIGHPHY gave 14.6% and 22.8% higher ileal digestibility coefficients for Ca and P, respectively, than for feed supplemented with exogenous HAP phytase at 500 FTU. This indicates that in planta wheat PAPhys has promising potential for improving P and mineral digestibility in animal feed
Resolving the shocked gas in HH54 with Herschel: CO line mapping at high spatial and spectral resolution
The HH54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II
cloud. Observed CO line profiles are due to a complex distribution in density,
temperature, velocity, and geometry. Resolving the HH54 shock wave in the
far-infrared cooling lines of CO constrain the kinematics, morphology, and
physical conditions of the shocked region. We used the PACS and SPIRE
instruments on board the Herschel space observatory to map the full FIR
spectrum in a region covering the HH54 shock wave. Complementary Herschel-HIFI,
APEX, and Spitzer data are used in the analysis as well. The observed features
in the line profiles are reproduced using a 3D radiative transfer model of a
bow-shock, constructed with the Line Modeling Engine code (LIME). The FIR
emission is confined to the HH54 region and a coherent displacement of the
location of the emission maximum of CO with increasing J is observed. The peak
positions of the high-J CO lines are shifted upstream from the lower J CO lines
and coincide with the position of the spectral feature identified previously in
CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the
upstream gas with distinct dynamics. The coherent displacement with increasing
J for CO is consistent with a scenario where IRAS12500-7658 is the exciting
source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K)
molecular component located upstream from the apex of the shock and blueshifted
by -7 km s. The spatial proximity of this knot to the peaks of the
atomic fine-structure emission lines observed with Spitzer and PACS ([OI]63,
145 m) suggests that it may be associated with the dissociative shock as
the jet impacts slower moving gas in the HH54 bow-shock.Comment: 6 pages, 5 figure
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