171 research outputs found
CO and CH3OH observations of the BHR71 outflows with APEX
Context : Highly-collimated outflows are believed to be the earliest stage in
outflow evolution, so their study is essential for understanding the processes
driving outflows. The BHR71 Bok globule is known to harbour such a
highly-collimated outflow, which is powered by a protostar belonging to a
protobinary system. Aims : We aimed at investigating the interaction of
collimated outflows with the ambient molecular cloud by using molecular
tracers. Methods : We mapped the BHR71 highly-collimated outflow in CO(3-2)
with the APEX telescope, and observed several bright points of the outflow in
the molecular transitions CO(4-3), 13CO(3-2), C18O(3-2), and CH3OH(7-6). We use
an LVG code to characterise the temperature enhancements in these regions.
Results : In our CO(3-2) map, the second outflow driven by IRS2, which is the
second source of the binary system, is completely revealed and shown to be
bipolar. We also measure temperature enhancements in the lobes. The CO and
methanol LVG modelling points to temperatures between 30 and 50K in the IRS1
outflow, while the IRS2 outflow seems to be warmer (up to 300K).Comment: 4 pages, 5 Figures, accepted by A&A Letters, to appear in the APEX
First results special issu
H2CO and CH3OH maps of the Orion Bar photodissociation region
A previous analysis of methanol and formaldehyde towards the Orion Bar
concluded that the two molecular species may trace different physical
components, methanol the clumpy material, and formaldehyde the interclump
medium. To verify this hypothesis, we performed multi-line mapping observations
of the two molecules to study their spatial distributions. The observations
were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular
resolution of ~11''. Additional data for H2CO from the Plateau de Bure array
are also discussed. The data were analysed using an LVG approach.
Both molecules are detected in our single-dish data. Our data show that CH3OH
peaks towards the clumps of the Bar, but its intensity decreases below the
detection threshold in the interclump material. When averaging over a large
region of the interclump medium, the strongest CH3OH line is detected with a
peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also
detected in the interclump gas. We verified that the weak intensity of CH3OH in
the interclump medium is not caused by the different excitation conditions of
the interclump material, but reflects a decrease in the column density of
methanol. The abundance of CH3OH relative to H2CO decreases by at least one
order of magnitude from the dense clumps to the interclump medium.Comment: 11 pages, accepted for publication in A&
Fast deuterium fractionation in magnetized and turbulent filaments
Deuterium fractionation is considered as an important process to infer the
chemical ages of prestellar cores in filaments. We present here the first
magneto-hydrodynamical simulations including a chemical network to study
deuterium fractionation in magnetized and turbulent filaments and their
substructures. The filaments typically show widespread deuterium fractionation
with average values . For individual cores of similar age, we
observe the deuteration fraction to increase with time, but also to be
independent of their average properties such as density, virial or
mass-to-magnetic flux ratio. We further find a correlation of the deuteration
fraction with core mass, average H density and virial parameter only at
late evolutionary stages of the filament and attribute this to the lifetime of
the individual cores. Specifically, chemically old cores reveal higher
deuteration fractions. Within the radial profiles of selected cores, we notice
differences in the structure of the deuteration fraction or surface density,
which we can attribute to their different turbulent properties. High
deuteration fractions of the order may be reached within
approximately ~kyrs, corresponding to two free-fall times, as defined for
cylindrical systems, of the filamentsComment: submitted to MNRAS. Comments welcom
The evolutionary state of the southern dense core Cha-MMS1
Aims: Our goal is to set constraints on the evolutionary state of the dense
core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze
molecular line observations carried out with the new submillimeter telescope
APEX. We look for outflow signatures around the dense core and probe its
chemical structure, which we compare to predictions of models of gas-phase
chemistry. We also use the public database of the Spitzer Space Telescope (SST)
to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F,
which are at the same distance. Results: We measure a large deuterium
fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core
L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+
(2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from
the high-density inner region. Our CO(3-2) map reveals the presence of a
bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not
find evidence for an outflow powered by Cha-MMS1. We also report the detection
of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a
level nearly an order of magnitude lower than IRAM 04191 and L1521F.
Conclusions: Cha-MMS1 appears to have already formed a compact object, either
the first hydrostatic core at the very end of the prestellar phase, or an
extremely young protostar that has not yet powered any outflow, at the very
beginning of the Class 0 accretion phase.Comment: Accepted by Astronomy & Astrophysics as a letter, to appear in the
special issue on the APEX first result
Synergy of multifrequency studies from observations of NGC6334I
We combine multifrequency observations from the millimeter to near infrared
wavelengths that demonstrate the spatial distributions of H2, CO, and NH3
emission, which are all manifestations of various shocks driven by outflows of
deeply embedded sources in NGC6334I. In addition to the well-known
northeast-southwest outflow we detect at least one more outflow in the region
by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC.
Potential driving sources will be discussed. NGC6334I exhibits several signs of
active star formation and will be a major target for future observatories such
as Herschel and ALMA.Comment: 6 pages, 6 figures, appeared in the proceedings of the workshop 'The
Universe Under The Microscope - Astrophysics At High Angular Resolution', see
http://www.iop.org/EJ/toc/1742-6596/131/
High mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky
We present molecular line observations of the massive star forming region
IRAS 17233-3606 aimed at studying the molecular core associated with the
source. The observations were made using the Atacama Pathfinder Experiment
telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH
(6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+
(4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical
angular resolution of the data is ~18''. Our observations reveal an
exceptionally rich molecular spectrum, a signpost of hot core activity.
Comparisons with two other prominent southern hot cores were made through
observations in the same frequency setups. We also detected a bipolar outflow
in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3''
and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the
molecular outflow are derived through the analysis of the CO (3-2) emission,
and are typical of outflows driven by high-mass young stellar objects.Comment: 9 pages, 10 figures (plus 8 figures as Online material), accepted by
A&
Water and acetaldehyde in HH212: The first hot corino in Orion
Aims: Using the unprecedented combination of high resolution and sensitivity
offered by ALMA, we aim to investigate whether and how hot corinos,
circumstellar disks, and ejected gas are related in young solar-mass
protostars. Methods: We observed CHCHO and deuterated water (HDO)
high-excitation ( up to 335 K) lines towards the Sun-like protostar
HH212--MM1. Results: For the first time, we have obtained images of CHCHO
and HDO emission in the inner 100 AU of HH212. The multifrequency line
analysis allows us to contrain the density ( 10 cm),
temperature ( 100 K), and CHCHO abundance ( 0.2--2
10) of the emitting region. The HDO profile is asymmetric at low
velocities ( 2 km s from ). If the HDO line is
optically thick, this points to an extremely small ( 20--40 AU) and dense
( 10 cm) emitting region. Conclusions: We report the first
detection of a hot corino in Orion. The HDO asymmetric profile indicates a
contribution of outflowing gas from the compact central region, possibly
associated with a dense disk wind.Comment: Astronomy & Astrophysics Letter, in pres
Water emission from the high-mass star-forming region IRAS 17233-3606. High water abundances at high velocities
We investigate the physical and chemical processes at work during the
formation of a massive protostar based on the observation of water in an
outflow from a very young object previously detected in H2 and SiO in the IRAS
17233-3606 region. We estimated the abundance of water to understand its
chemistry, and to constrain the mass of the emitting outflow. We present new
observations of shocked water obtained with the HIFI receiver onboard Herschel.
We detected water at high velocities in a range similar to SiO. We
self-consistently fitted these observations along with previous SiO data
through a state-of-the-art, one-dimensional, stationary C-shock model. We found
that a single model can explain the SiO and H2O emission in the red and blue
wings of the spectra. Remarkably, one common area, similar to that found for H2
emission, fits both the SiO and H2O emission regions. This shock model
subsequently allowed us to assess the shocked water column density,
N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum
fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The
corresponding water abundance in fractional column density units ranges between
2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in
outflows from low- and high-mass young stellar objects.Comment: accepted for publication as a Letter in Astronomy and Astrophysic
Extremely high velocity gas from the massive YSOs in IRAS 17233-3606
Molecular outflows from high-mass young stellar objects provide an excellent
way to study the star formation process, and investigate if they are scaled-up
versions of their low-mass counterparts. We selected the nearby massive star
forming region IRAS 17233-3606 in order to study the kinematics and physics
along the molecular outflow(s) originating from this source. We observed IRAS
17233-3606 in CO, a typical tracer of gas associated with molecular outflow,
with the Submillimeter Array in the (2-1) transition, and with the APEX
telescope in the higher excitation (6-5) line. Additional infrared H2
observations were performed with the UKIRT telescope. The CO data were analysed
using a LVG approach. Our data resolve the previously detected molecular
outflow in at least three different components, one of them with a high
collimation factor ~4, and characterised by emission at extremely high
velocities (|v-v_{LSR}|>120 km s^{-1}). The estimate of the kinematical outflow
parameters are typical of massive YSOs, and in agreement with the measured
bolometric luminosity of the source. The kinematic ages of the flows are in the
range 10^2-10^3 yr, and therefore point to young objects that still did not
reach the main sequence.Comment: accepted for publication in A&
A timeline for massive star-forming regions via combined observation of o-HD and ND
Context: In cold and dense gas prior to the formation of young stellar
objects, heavy molecular species (including CO) are accreted onto dust grains.
Under these conditions H and its deuterated isotopologues become more
abundant, enhancing the deuterium fraction of molecules such as NH that
are formed via ion-neutral reactions. Because this process is extremely
temperature sensitive, the abundance of these species is likely linked to the
evolutionary stage of the source.
Aims: We investigate how the abundances of o-HD and ND vary
with evolution in high-mass clumps.
Methods: We observed with APEX the ground-state transitions of o-HD
near 372 GHz, and ND(3-2) near 231 GHz for three massive clumps in
different evolutionary stages. The sources were selected within the
G351.77-0.51 complex to minimise the variation of initial chemical conditions,
and to remove distance effects. We modelled their dust continuum emission to
estimate their physical properties, and also modelled their spectra under the
assumption of local thermodynamic equilibrium to calculate beam-averaged
abundances.
Results: We find an anticorrelation between the abundance of o-HD and
that of ND, with the former decreasing and the latter increasing with
evolution. With the new observations we are also able to provide a qualitative
upper limit to the age of the youngest clump of about 10 yr, comparable to
its current free-fall time.
Conclusions: We can explain the evolution of the two tracers with simple
considerations on the chemical formation paths, depletion of heavy elements,
and evaporation from the grains. We therefore propose that the joint
observation and the relative abundance of o-HD and ND can act
as an efficient tracer of the evolutionary stages of the star-formation
process
- …