1,341 research outputs found
Sub-arcsecond SMA observations of the prototype Class 0 object VLA1623 at 1.3 mm: A single protostar with a structured outflow cavity ?
We present 1.3-mm subarcsecond SMA observations of the prototypical Class 0
protostar VLA1623. We report the detection of 1.3-mm continuum emission both
from the central protostellar component VLA1623 and two additional sources,
Knot-A and Knot-B, which have been already detected at longer wavelengths.
Knot-A and Knot-B are both located along the western cavity wall opened by the
protostellar outflow from VLA1623. Our SMA observations moreover show that
these two continuum sources are associated with bright, high-velocity 12CO(2-1)
emission, slightly shifted downstream of the outflow propagation direction with
respect to the 1.3-mm continuum emission peaks. The alignment of Knot-A and
Knot-B along the protostellar outflow cavity, the compactness of their 1.3-mm
continuum emission and the properties of the associated CO emission suggest
that these two sources trace outflow features due to shocks along the cavity
wall, rather than protostellar objects. While it was considered as one of the
best examples of a close protobinary system so far, the present analysis
suggests that the prototypical Class 0, VLA1623, is single on the scales a>100
AU probed by our SMA observations. Moreover, we present here the second robust
case of compact millimeter continuum emission produced by interactions between
the protostellar jet and the envelope of a Class 0 protostar, which suggests a
high occurrence of these outflow features during the embedded phase.Comment: Accepted for publication in Astronomy and Astrophysics. Low
resolution figure
Connecting the Contradictory with Science Art and the Aid of a Caption
When the disciplines of science and art intertwine to reveal a truth then words and images are suited to telling different parts, and reveal the whole story most effectively when working in tandem. Decoding the underlying science within a work of art through a caption does not diminish its value as art, but when we fail to decode the science we miss entry into a narrative
The influence of the phosphorus and calcium content of feeds on growth, feed conversion and slaughter quality, and on the chemical, mechanical and histological parameters of the bone tissue of pigs.
In a 2 X 4 factorial experiment on 96 individually housed pigs, 2 calcium/phosphorus ratios (1.3 and 1.9) and 4 phosphorus levels (0.4, 0.5, 0.6, 0.7% total P) were tested. The influence of the treatments on growth, feed conversion and slaughter quality was measured. The experiment showed the 1.3 Ca/P ratio to be more favourable than the 1.9 ratio. A P content of 0.6% was sufficient for good growth and favourable feed conversion. The quality of the bone tissue, for which the specific response resistance to distortion and breaking was used as a standard, was close to maximum when P in the feed was 0.6%. The strength of the whole bone, measured as the bending moment for distortion and breaking, was greatest when P was highest; mineralization of the bone also showed a further increase when the P content in the feed increased from 0.6 to 0.7%.During the experiment only a few cases of leg weakness were noted; these occurred throughout all the experimental treatments. On the basis of the results, the P and Ca requirements for optimal growth and feed conversion for the modern Dutch pig are 0.6% and 0.78%. More of these minerals in the feed may, however, increase deposition in the skeleton. (Abstract retrieved from CAB Abstracts by CABI’s permission
Testing particle trapping in transition disks with ALMA
We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum
observations at 336GHz of two transition disks, SR21 and HD135344B. In
combination with previous ALMA observations from Cycle 0 at 689GHz, we compare
the visibility profiles at the two frequencies and calculate the spectral index
(). The observations of SR21 show a clear shift in the
visibility nulls, indicating radial variations of the inner edge of the cavity
at the two wavelengths. Notable radial variations of the spectral index are
also detected for SR21 with values of in the
inner region ( AU) and outside. An
axisymmetric ring (which we call the ring model) or a ring with the addition of
an azimuthal Gaussian profile, for mimicking a vortex structure (which we call
the vortex model), is assumed for fitting the disk morphology. For SR21, the
ring model better fits the emission at 336GHz, conversely the vortex model
better fits the 689GHz emission. For HD135344B, neither a significant shift in
the null of the visibilities nor radial variations of are
detected. Furthermore, for HD135344B, the vortex model fits both frequencies
better than the ring model. However, the azimuthal extent of the vortex
increases with wavelength, contrary to model predictions for particle trapping
by anticyclonic vortices. For both disks, the azimuthal variations of
remain uncertain to confirm azimuthal trapping. The
comparison of the current data with a generic model of dust evolution that
includes planet-disk interaction suggests that particles in the outer disk of
SR21 have grown to millimetre sizes and have accumulated in a radial pressure
bump, whereas with the current resolution there is not clear evidence of radial
trapping in HD135344B, although it cannot be excluded either.Comment: Minor changes after language edition. Accepted for publication in A&A
(abstract slightly shortened for arXiv
APEX-CHAMP+ high-J CO observations of low-mass young stellar objects: II. Distribution and origin of warm molecular gas
The origin and heating mechanisms of warm (50<T<200 K) molecular gas in
low-mass young stellar objects (YSOs) are strongly debated. Both passive
heating of the inner collapsing envelope by the protostellar luminosity as well
as active heating by shocks and by UV associated with the outflows or accretion
have been proposed. We aim to characterize the warm gas within protosteller
objects, and disentangle contributions from the (inner) envelope, bipolar
outflows and the quiescent cloud. High-J CO maps (12CO J=6--5 and 7--6) of the
immediate surroundings (up to 10,000 AU) of eight low-mass YSOs are obtained
with the CHAMP+ 650/850 GHz array receiver mounted on the APEX telescope. In
addition, isotopologue observations of the 13CO J=6--5 transition and [C I]
3P_2-3P_1 line were taken. Strong quiescent narrow-line 12CO 6--5 and 7--6
emission is seen toward all protostars. In the case of HH~46 and Ced 110 IRS 4,
the on-source emission originates in material heated by UV photons scattered in
the outflow cavity and not just by passive heating in the inner envelope. Warm
quiescent gas is also present along the outflows, heated by UV photons from
shocks. Shock-heated warm gas is only detected for Class 0 flows and the more
massive Class I sources such as HH~46. Outflow temperatures, estimated from the
CO 6--5 and 3--2 line wings, are ~100 K, close to model predictions, with the
exception of the L~1551 IRS 5 and IRAS 12496-7650, for which temperatures <50 K
are found. APEX-CHAMP+ is uniquely suited to directly probe a protostar's
feedback on its accreting envelope gas in terms of heating, photodissociation,
and outflow dispersal by mapping 1'x1' regions in high-J CO and [C I] lines.Comment: 18 pages, accepted by A&A, A version with the figures in higher
quality can be found on my website: http://www.cfa.harvard.edu/~tvankemp
The hot core towards the intermediate mass protostar NGC7129 FIRS 2: Chemical similarities with Orion KL
NGC 7129 FIRS 2 (hereafter FIRS 2) is an intermediate-mass (2 to 8 Msun)
protostar located at a distance of 1250 pc. High spatial resolution
observations are required to resolve the hot core at its center. We present a
molecular survey from 218200 MHz to 221800 MHz carried out with the IRAM
Plateau de Bure Interferometer. These observations were complemented with a
long integration single-dish spectrum taken with the IRAM 30m telescope. We
used a Local Thermodynamic Equilibrium (LTE) single temperature code to model
the whole dataset. The interferometric spectrum is crowded with a total of ~300
lines from which a few dozens remain unidentified yet. The spectrum has been
modeled with a total of 20 species and their isomers, isotopologues and
deuterated compounds. Complex molecules like methyl formate (CH3OCHO), ethanol
(CH3CH2OH), glycolaldehyde (CH2OHCHO), acetone (CH3COCH3), dimethyl ether
(CH3OCH3), ethyl cyanide (CH3CH2CN) and the aGg' conformer of ethylene glycol
(aGg'-(CH2OH)_2) are among the detected species. The detection of vibrationally
excited lines of CH3CN, CH3OCHO, CH3OH, OCS, HC3N and CH3CHO proves the
existence of gas and dust at high temperatures. In fact, the gas kinetic
temperature estimated from the vibrational lines of CH3CN, ~405 K, is similar
to that measured in massive hot cores. Our data allow an extensive comparison
of the chemistry in FIRS~2 and the Orion hot core. We find a quite similar
chemistry in FIRS 2 and Orion. Most of the studied fractional molecular
abundances agree within a factor of 5. Larger differences are only found for
the deuterated compounds D2CO and CH2DOH and a few molecules (CH3CH2CN, SO2,
HNCO and CH3CHO). Since the physical conditions are similar in both hot cores,
only different initial conditions (warmer pre-collapse phase in the case of
Orion) and/or different crossing time of the gas in the hot core can explain
this behavior.Comment: 30 pages, 9 figure
A Major Asymmetric Dust Trap in a Transition Disk
The statistics of discovered exoplanets suggest that planets form
efficiently. However, there are fundamental unsolved problems, such as
excessive inward drift of particles in protoplanetary disks during planet
formation. Recent theories invoke dust traps to overcome this problem. We
report the detection of a dust trap in the disk around the star Oph IRS 48
using observations from the Atacama Large Millimeter/submillimeter Array
(ALMA). The 0.44-millimeter-wavelength continuum map shows high-contrast
crescent-shaped emission on one side of the star originating from
millimeter-sized grains, whereas both the mid-infrared image (micrometer-sized
dust) and the gas traced by the carbon monoxide 6-5 rotational line suggest
rings centered on the star. The difference in distribution of big grains versus
small grains/gas can be modeled with a vortex-shaped dust trap triggered by a
companion.Comment: 25 pages, 7 figures (accepted version prior to language editing
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