1,077 research outputs found
Dense and warm molecular gas in the envelopes and outflows of southern low-mass protostars
Observations of dense molecular gas lie at the basis of our understanding of
the density and temperature structure of protostellar envelopes and molecular
outflows. We aim to characterize the properties of the protostellar envelope,
molecular outflow and surrounding cloud, through observations of high
excitation molecular lines within a sample of 16 southern sources presumed to
be embedded YSOs. Observations of submillimeter lines of CO, HCO+ and their
isotopologues, both single spectra and small maps were taken with the FLASH and
APEX-2a instruments mounted on APEX to trace the gas around the sources. The
HARP-B instrument on the JCMT was used to map IRAS 15398-3359 in these lines.
HCO+ mapping probes the presence of dense centrally condensed gas, a
characteristic of protostellar envelopes. The rare isotopologues C18O and
H13CO+ are also included to determine the optical depth, column density, and
source velocity. The combination of multiple CO transitions, such as 3-2, 4-3
and 7-6, allows to constrain outflow properties, in particular the temperature.
Archival submillimeter continuum data are used to determine envelope masses.
Eleven of the sixteen sources have associated warm and/or dense quiescent as
characteristic of protostellar envelopes, or an associated outflow. Using the
strength and degree of concentration of the HCO+ 4-3 and CO 4-3 lines as a
diagnostic, five sources classified as Class I based on their spectral energy
distributions are found not to be embedded YSOs. The C18O 3-2 lines show that
for none of the sources, foreground cloud layers are present. Strong molecular
outflows are found around six sources, .. (continued in paper)Comment: Accepted by A&A, 13 figure
Feshbach resonances with large background scattering length: interplay with open-channel resonances
Feshbach resonances are commonly described by a single-resonance Feshbach
model, and open-channel resonances are not taken into account explicitly.
However, an open-channel resonance near threshold limits the range of validity
of this model. Such a situation exists when the background scattering length is
much larger than the range of the interatomic potential. The open-channel
resonance introduces strong threshold effects not included in the
single-resonance description. We derive an easy-to-use analytical model that
takes into account both the Feshbach resonance and the open-channel resonance.
We apply our model to Rb, which has a large background scattering
length, and show that the agreement with coupled-channels calculations is
excellent. The model can be readily applied to other atomic systems with a
large background scattering length, such as Li and Cs. Our approach
provides full insight into the underlying physics of the interplay between
open-channel (or potential) resonances and Feshbach resonances.Comment: 16 pages, 12 figures, accepted for publication in Phys. Rev. A; v2:
added reference
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
Resolved gas cavities in transitional disks inferred from CO isotopologues with ALMA
Transitional disks around young stars are promising candidates to look for
recently formed, embedded planets. Planet-disk interaction models predict that
planets clear a gap in the gas while trapping dust at larger radii. Other
physical mechanisms could be responsible for cavities as well. Previous
observations have revealed that gas is still present inside these cavities, but
the spatial distribution of this gas remains uncertain. We present high spatial
resolution observations with the Atacama Large Millimeter/submillimeter Array
(ALMA) of 13CO and C18O lines of four well-studied transitional disks. The
observations are used to set constraints on the gas surface density,
specifically cavity size and density drop inside the cavity. The
physical-chemical model DALI is used to analyze the gas images of SR21,
HD135344B, DoAr44 and IRS48. The main parameters of interest are the size,
depth and shape of the gas cavity. CO isotope-selective photodissociation is
included to properly constrain the surface density in the outer disk from C18O
emission. The gas cavities are up to 3 times smaller than those of the dust in
all four disks. Model fits indicate that the surface density inside the gas
cavities decreases by a factor of 100-10000 compared with the surface density
profile derived from the outer disk. A comparison with an analytical model of
gap depths by planet-disk interaction shows that the disk viscosities are
likely low, with a<1E-3 for planet masses <10 MJup. The resolved measurements
of the gas and dust in transition disk cavities support the predictions of
models that describe how planet-disk interactions sculpt gas disk structures
and influence the evolution of dust grains. These observed structures strongly
suggest the presence of giant planetary companions in transition disk cavities,
although at smaller orbital radii than is typically indicated from the dust
cavity radii alone.Comment: Accepted by A&A; version after language-editin
APEX-CHAMP+ high-J CO observations of low-mass young stellar objects: III. NGC 1333 IRAS 4A/4B envelope, outflow and UV heating
NGC 1333 IRAS 4A and IRAS 4B sources are among the best studied Stage 0
low-mass protostars which are driving prominent bipolar outflows. Most studies
have so far concentrated on the colder parts (T<30K) of these regions. The aim
is to characterize the warmer parts of the protostellar envelope in order to
quantify the feedback of the protostars on their surroundings in terms of
shocks, UV heating, photodissociation and outflow dispersal. Fully sampled
large scale maps of the region were obtained; APEX-CHAMP+ was used for 12CO
6-5, 13CO 6-5 and [CI] 2-1, and JCMT-HARP-B for 12CO 3-2 emissions.
Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs,
from 1-0 upto 10-9 (Eu/k 300K), are collected at the source positions.
Radiative-transfer models of the dust and lines are used to determine
temperatures and masses of the outflowing and UV-heated gas and infer the CO
abundance structure. Broad CO emission line profiles trace entrained shocked
gas along the outflow walls, with typical temperatures of ~100K. At other
positions surrounding the outflow and the protostar, the 6-5 line profiles are
narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the
UV heated gas distribution for the first time. The amount of UV-heated and
outflowing gas are found to be comparable from the 12CO and 13CO 6-5 maps,
implying that UV photons can affect the gas as much as the outflows. Weak [CI]
emission throughout the region indicates a lack of CO dissociating photons.
Modeling of the C18O lines indicates the necessity of a "drop" abundance
profile throughout the envelope where the CO freezes out and is reloaded back
into the gas phase, thus providing quantitative evidence for the CO ice
evaporation zone around the protostars. The inner abundances are less than the
canonical value of CO/H_2=2.7x10^-4, indicating some processing of CO into
other species on the grains.Comment: 20 pages, 22 figures, Accepted by A&
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
Warm formaldehyde in the Oph IRS 48 transitional disk
Simple molecules like H2CO and CH3OH in protoplanetary disks are the starting
point for the production of more complex organic molecules. So far, the
observed chemical complexity in disks has been limited due to freeze out of
molecules onto grains in the bulk of the cold outer disk. Complex molecules can
be studied more directly in transitional disks with large inner holes, as these
have a higher potential of detection, through UV heating of the outer disk and
the directly exposed midplane at the wall. We use Atacama Large
Millimeter/submillimeter Array (ALMA) Band 9 (~680 GHz) line data of the
transitional disk Oph IRS 48, previously shown to have a large dust trap, to
search for complex molecules in regions where planetesimals are forming. We
report the detection of the H2CO 9(1,8)-8(1,7) line at 674 GHz, which is
spatially resolved as a semi-ring at ~60 AU radius centered south from the
star. The inferred H2CO abundance is ~10^{-8} derived by combining a physical
disk model of the source with a non-LTE excitation calculation. Upper limits
for CH3OH lines in the same disk give an abundance ratio H2CO/CH3OH>0.3, which
points to both ice formation and gas-phase routes playing a role in the H2CO
production. Upper limits on the abundances of H13CO+, CN and several other
molecules in the disk are also derived and found to be consistent with full
chemical models. The detection of the H2CO line demonstrates the start of
complex organic molecules in a planet-forming disk. Future ALMA observations
should be able to push down the abundance detection limits of other molecules
by 1-2 orders of magnitude and test chemical models of organic molecules in
(transitional) disks.Comment: Updated references and minor changes to text, approved by language
edito
Advancing interoperable soil data exchange for global soil data information systems
In order to be able to address local, regional and global issues such as sustainable land management, food security, climate change mitigation and soil-related indicators of the UN Agenda for Sustainable Development the need for reliable, relevant and accurate soil information and data is increasing. Currently, ..
Development of a smoking abstinence self-efficacy questionnaire
BACKGROUND: Self-efficacy beliefs are an important determinant of (changes in) health behaviors. In the area of smoking cessation, there is a need for a short, feasible, and validated questionnaire measuring self-efficacy beliefs regarding smoking cessation. PURPOSE: The purpose of this study is to investigate the psychometric properties of a six-item questionnaire to assess smoking cessation self-efficacy. METHODS: We used longitudinal data from a smoking cessation study. A total of 513 smokers completed the Smoking Abstinence Self-efficacy Questionnaire (SASEQ) and questionnaires assessing depressive symptoms and motivation to quit smoking. After that, they set a quit date and attempted to stop smoking. One year after the quit date, smoking status of participants was assessed by self report. The psychometric properties of the SASEQ were studied and we investigated whether SASEQ scores predicted successful smoking cessation. RESULTS: Factor analysis yielded one factor, with an Eigenvalue of 3.83, explaining 64% of variance. All factor loadings were ≥0.73. We found a Cronbach’s alpha of 0.89 for the SASEQ, low correlations for the SASEQ with depressive symptoms, and motivation to quit, indicating that self-efficacy is measured independently of these concepts. Furthermore, high baseline SASEQ scores significantly predicted smoking abstinence at 52 weeks after the quit date (OR = 1.85; 95% CI = 1.20~2.84). CONCLUSIONS: The SASEQ appeared to be a short, reliable, and valid questionnaire to assess self-efficacy beliefs regarding smoking abstinence. In the present study, this instrument also had good predictive validity. The short SASEQ can easily be used in busy clinical practice to guide smoking cessation interventions
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