1,173 research outputs found
Dust, Ice, and Gas In Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Chamaeleontis
Aims. We aim to study the composition and energetics of the circumstellar material of DK Cha, an intermediate-mass star in transition from an
embedded configuration to a star plus disk stage, during this pivotal stage of its evolution.
Methods. Using the range scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 μm as part
of the DIGIT key program.
Results. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO
from J = 14–13 to 38–37 (E_u/k = 4080 K), water from levels as excited as J_(K−1 K+1) = 7_(07) (E_u/k = 843 K), and OH lines up to E_u/k = 290 K were
detected.
Conclusions. The continuum emission in our PACS SED scan matches the flux expected by a model consisting of a star, a surrounding disk of
0.03 M_⊙, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic,
and ionic emission lines in the far-infrared reveal the outflow’s influence on the envelope. The inferred hot gas may be photon-heated, but some
emission may be caused by C-shocks in the walls of the outflow cavity
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
The origin of organic emission in NGC 2071
Context: The physical origin behind organic emission in embedded low-mass
star formation has been fiercely debated in the last two decades. A multitude
of scenarios have been proposed, from a hot corino to PDRs on cavity walls to
shock excitation.
Aims: The aim of this paper is to determine the location and the
corresponding physical conditions of the gas responsible for organics emission
lines. The outflows around the small protocluster NGC 2071 are an ideal testbed
to differentiate between various scenarios.
Methods: Using Herschel-HIFI and the SMA, observations of CH3OH, H2CO and
CH3CN emission lines over a wide range of excitation energies were obtained.
Comparisons to a grid of radiative transfer models provide constraints on the
physical conditions. Comparison to H2O line shape is able to trace gas-phase
synthesis versus a sputtered origin.
Results: Emission of organics originates in three spots: the continuum
sources IRS 1 ('B') and IRS 3 ('A') as well as a outflow position ('F').
Densities are above 10 cm and temperatures between 100 to 200 K.
CH3OH emission observed with HIFI originates in all three regions and cannot be
associated with a single region. Very little organic emission originates
outside of these regions.
Conclusions: Although the three regions are small (<1,500 AU), gas-phase
organics likely originate from sputtering of ices due to outflow activity. The
derived high densities (>10 cm) are likely a requirement for organic
molecules to survive from being destroyed by shock products. The lack of
spatially extended emission confirms that organic molecules cannot (re)form
through gas-phase synthesis, as opposed to H2O, which shows strong line wing
emission. The lack of CH3CN emission at 'F' is evidence for a different history
of ice processing due to the absence of a protostar at that location and recent
ice mantle evaporation.Comment: 10 Pages, 8 figures, Accepted for Astronomy and Astrophysic
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
Far infrared CO and HO emission in intermediate-mass protostars
Intermediate-mass young stellar objects (YSOs) provide a link to understand
how feedback from shocks and UV radiation scales from low to high-mass star
forming regions. Aims: Our aim is to analyze excitation of CO and HO in
deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass
YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with
bolometric luminosities of . The maps
cover spatial scales of AU in several CO and HO lines located
in the m range. Results: Rotational diagrams of CO show two
temperature components at K and
K, comparable to low- and high-mass protostars
probed at similar spatial scales. The diagrams for HO show a single
component at K, as seen in low-mass protostars, and
about K lower than in high-mass protostars. Since the uncertainties in
are of the same order as the difference between the
intermediate and high-mass protostars, we cannot conclude whether the change in
rotational temperature occurs at a specific luminosity, or whether the change
is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation
in intermediate-mass protostars is comparable to the central AU of
low-mass protostars and consistent within the uncertainties with the high-mass
protostars probed at AU scales, suggesting similar shock
conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table
A study of the relationship between health awareness, lifestyle behaviour and food label usage in Gauteng
Background: The objectives of the study were to determine whether consumers who read food labels, were also more aware of health and lifestyle issues, in terms of nutrition and other health-related lifestyle behaviours, and whether there was a relationship between food-label reading, health awareness and lifestyle behaviour. A quantitative descriptive (survey) design was selected to investigate the relationship between food-label reading on the one hand, and health awareness and lifestyle behavior on the other.Method: A two-stage, stratified-proportionate and systematic sampling strategy was applied to select a sample of 357 Gauteng respondents to complete a telephonic questionnaire. Respondents who were most likely to read food label information were selected. Food label information is prescribed by comprehensive label legislation. Data report on respondents’ label-reading habits, attitudes towards health awareness, lifestyle behaviour and biographic data. Nonparametric analysis, scale reliability tests, analysis of variance (ANOVA) and Bonferroni multiple comparisons of means tests were used to analyse the results.Results: Results indicate that the two-thirds of respondents who, to some extent read nutritional information on food labels, were concerned about their personal health, were interested in health-related information, and followed a healthy lifestyle, such as regularly eating fresh fruit and vegetables, cutting back on alcohol, and other positive lifestyle behaviours. They were unsure about how their own knowledge of nutrition,and their understanding of nutrition information on food labels, compared with that of other consumers.Conclusion: A relationship was found between patterns of reading food labels, health awareness and lifestyle behaviour. People who often read food labels were more health-conscious, and maintained a healthier lifestyle.Keywords: health awareness, lifestyle, food labels, South Africa, consumer
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