1,119 research outputs found
The clumpy structure of the chemically active L1157 outflow
We present high spatial resolution maps, obtained with the Plateau de Bure
Interferometer, of the blue lobe of the L1157 outflow. We observed four lines
at 3 mm, namely CH3OH (2_K-1_K), HC3N (11-10), HCN (1-0) and OCS (7-6).
Moreover, the bright B1 clump has also been observed at better spatial
resolution in CS (2-1), CH3OH (2_1-1_1)A-, and 34SO (3_2-2_1). These high
spatial resolution observations show a very rich structure in all the tracers,
revealing a clumpy structure of the gas superimposed to an extended emission.
In fact, the three clumps detected by previous IRAM-30m single dish
observations have been resolved into several sub-clumps and new clumps have
been detected in the outflow. The clumps are associated with the two cavities
created by two shock episodes driven by the precessing jet. In particular, the
clumps nearest the protostar are located at the walls of the younger cavity
with a clear arch-shape form while the farthest clumps have slightly different
observational characteristics indicating that they are associated to the older
shock episode. The emission of the observed species peaks in different part of
the lobe: the east clumps are brighter in HC3N (11-10), HCN (1-0) and CS (2-1)
while the west clumps are brighter in CH3OH(2_K-1_K), OCS (7-6) and 34SO
(3_2-2_1). This peak displacement in the line emission suggests a variation of
the physical conditions and/or the chemical composition along the lobe of the
outflow at small scale, likely related to the shock activity and the precession
of the outflow. In particular, we observe the decoupling of the silicon
monoxide and methanol emission, common shock tracers, in the B1 clump located
at the apex of the bow shock produced by the second shock episode.Comment: 11 pages, 8 figures, accepted for publication in the MNRA
First results from the CALYPSO IRAM-PdBI survey. I. Kinematics of the inner envelope of NGC1333-IRAS2A
The structure and kinematics of Class 0 protostars on scales of a few hundred
AU is poorly known. Recent observations have revealed the presence of Keplerian
disks with a diameter of 150-180 AU in L1527-IRS and VLA1623A, but it is not
clear if such disks are common in Class 0 protostars. Here we present
high-angular-resolution observations of two methanol lines in NGC1333-IRAS2A.
We argue that these lines probe the inner envelope, and we use them to study
the kinematics of this region. Our observations suggest the presence of a
marginal velocity gradient normal to the direction of the outflow. However, the
position velocity diagrams along the gradient direction appear inconsistent
with a Keplerian disk. Instead, we suggest that the emission originates from
the infalling and perhaps slowly rotating envelope, around a central protostar
of 0.1-0.2 M. If a disk is present, it is smaller than the disk of
L1527-IRS, perhaps suggesting that NGC1333-IRAS2A is younger.Comment: Accepted for publication in A&A letter
First results from the CALYPSO IRAM-PdBI survey - III. Monopolar jets driven by a proto-binary system in NGC1333-IRAS2A
Context: The earliest evolutionary stages of low-mass protostars are
characterised by hot and fast jets which remove angular momentum from the
circumstellar disk, thus allowing mass accretion onto the central object.
However, the launch mechanism is still being debated. Aims: We would like to
exploit high-angular (~ 0.8") resolution and high-sensitivity images to
investigate the origin of protostellar jets using typical molecular tracers of
shocked regions, such as SiO and SO. Methods: We mapped the inner 22" of the
NGC1333-IRAS2A protostar in SiO(5-4), SO(65-54), and the continuum emission at
1.4 mm using the IRAM Plateau de Bure interferometer in the framework of the
CALYPSO IRAM large program. Results: For the first time, we disentangle the
NGC1333-IRAS2A Class 0 object into a proto-binary system revealing two
protostars (MM1, MM2) separated by ~ 560 AU, each of them driving their own
jet, while past work considered a single protostar with a quadrupolar outflow.
We reveal (i) a clumpy, fast (up to |V-VLSR| > 50 km/s), and blueshifted jet
emerging from the brightest MM1 source, and (ii) a slower redshifted jet,
driven by MM2. Silicon monoxide emission is a powerful tracer of
high-excitation (Tkin > 100 K; n(H2) > 10^5 cm-3) jets close to the launching
region. At the highest velocities, SO appears to mimic SiO tracing the jets,
whereas at velocities close to the systemic one, SO is dominated by extended
emission, tracing the cavity opened by the jet. Conclusions: Both jets are
intrinsically monopolar, and intermittent in time. The dynamical time of the
SiO clumps is < 30-90 yr, indicating that one-sided ejections from protostars
can take place on these timescales.Comment: Astronomy & Astrophysics Letter, in pres
Heavy water around the L1448-mm protostar
Context: L1448-mm is the prototype of a low-mass Class 0 protostar driving a
high-velocity jet. Given its bright H2O spectra observed with ISO, L1448-mm is
an ideal laboratory to observe heavy water (HDO) emission. Aims: Our aim is to
image the HDO emission in the protostar surroundings, the possible occurrence
of HDO emission also investigating off L1448-mm, towards the molecular outflow.
Methods: We carried out observations of L1448-mm in the HDO(1_10-1_11) line at
80.6 GHz, an excellent tracer of HDO column density, with the IRAM Plateau de
Bure Interferometer. Results: We image for the first time HDO emission around
L1448-mm. The HDO structure reveals a main clump at velocities close to the
ambient one towards the the continuum peak that is caused by the dust heated by
the protostar. In addition, the HDO map shows tentative weaker emission at
about 2000 AU from the protostar towards the south, which is possibly
associated with the walls of the outflow cavity opened by the protostellar
wind. Conclusions: Using an LVG code, modelling the density and temperature
profile of the hot-corino, and adopting a gas temperature of 100 K and a
density of 1.5 10^8 cm^-3, we derive a beam diluted HDO column density of about
7 10^13 cm^-2, corresponding to a HDO abundance of about 4 10^-7. In addition,
the present map supports the scenario where HDO can be efficiently produced in
shocked regions and not uniquely in hot corinos heated by the newly born star.Comment: Accepted by A&A as Letter; 5 pages, 3 figure
The Propagation of Magneto-Centrifugally Launched Jets: I
We present simulations of the propagation of magnetized jets. This work
differs from previous studies in that the cross-sectional distributions of the
jets's state variables are derived from analytical models for
magneto-centrifugal launching. The source is a magnetized rotator whose
properties are specfied as boundary conditions. The jets in these simulations
are considerably more complex than the ``top-hat''constant density etc.
profiles used in previous work. We find that density and magnetic field
stratification (with radius) in the jet leads to new behavior including the
separation of an inner jet core from a low density collar. We find this {\it
jet within a jet} structure, along with the magnetic stresses, leads to
propagation behaviors not observed in previous simulation studies. Our
methodology allows us to compare MHD jets from different types of sources whose
properties could ultimately be derived from the behavior of the propagating
jets.Comment: 42 pages, accepted by the Ap
Spitzer spectral line mapping of protostellar outflows: II H2 emission in L1157
We present an analysis of Spitzer-IRS spectroscopic maps of the L1157
protostellar outflow in the H2 pure-rotational lines from S(0) to S(7). The aim
of this work is to derive the physical conditions pertaining to the warm
molecular gas and study their variations within the flow. The mid-IR H2
emission follows the morphology of the precessing flow, with peaks correlated
with individual CO clumps and H2 2.12{\mu}m ro-vibrational emission. More
diffuse emission delineating the CO cavities is detected only in the low-laying
transitions, with J(lower) less or equal to 2. The H2 line images have been
used to construct 2D maps of N(H2), H2 ortho-to-para ratio and temperature
spectral index beta, in the assumption of a gas temperature stratification
where the H2 column density varies as T^(beta). Variations of these parameters
are observed along the flow. In particular, the ortho-to-para ratio ranges from
0.6 to 2.8, highlighting the presence of regions subject to recent shocks where
the ortho-to-para ratio has not had time yet to reach the equilibrium value.
Near-IR spectroscopic data on ro-vibrational H2 emission have been combined
with the mid-IR data and used to derive additional shock parameters in the
brightest blue- and red-shifted emission knots. A high abundance of atomic
hydrogen (H/H2 about 0.1-0.3) is implied by the observed H2 column densities,
assuming n(H2) values as derived by independent SiO observations. The presence
of a high fraction of atomic hydrogen, indicates that a partially-dissociative
shock component should be considered for the H2 excitation in these localized
regions. However, planar shock models, either of C- or J-type, are not able to
consistently reproduce all the physical parameters derived from our analysis of
the H2 emission. Globally, H2 emission contributes to about 50% of the total
shock radiated energy in the L1157 outflow.Comment: 31 pages, 9 figure, Accepted for publication on Ap
The ortho-to-para ratio of ammonia in the L1157 outflow
We have measured the ortho-to-para ratio of ammonia in the blueshifted gas of
the L1157 outflow by observing the six metastable inversion lines from (J, K) =
(1, 1) to (6, 6). The highly excited (5, 5) and (6, 6) lines were first
detected in the low-mass star forming regions. The rotational temperature
derived from the ratio of four transition lines from (3, 3) to (6, 6) is
130-140 K, suggesting that the blueshifted gas is heated by a factor of ~10 as
compared to the quiescent gas. The ortho-to-para ratio of the NH3 molecules in
the blueshifted gas is estimated to be 1.3--1.7, which is higher than the
statistical equilibrium value. This ratio provides us with evidence that the
NH3 molecules have been evaporated from dust grains with the formation
temperature between 18 and 25 K. It is most likely that the NH3 molecules on
dust grains have been released into the gas phase through the passage of strong
shock waves produced by the outflow. Such a scenario is supported by the fact
that the ammonia abundance in the blueshifted gas is enhanced by a factor of ~5
with respect to the dense quiescent gas.Comment: 16 pages, including 3 PS figures. To appear in the ApJ (Letters).
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Discovery of superthermal hydroxyl (OH) in the HH211 outflow
We present a 5-37 micron infrared spectrum obtained with the Spitzer Space
Telescope toward the southeastern lobe of the young protostellar outflow HH211.
The spectrum shows an extraordinary sequence of OH emission lines arising in
highly excited rotational levels up to an energy E/k~28200K above the ground
level. This is, to our knowledge, by far the highest rotational excitation of
OH observed outside Earth. The spectrum also contains several pure rotational
transitions of H2O (v=0), H2 (v=0) S(0) to S(7), HD (v=0) R(3) to R(6), and
atomic fine-structure lines of [Fe II], [Si II], [Ne II], [S I], and [Cl I].
The origin of the highly excited OH emission is most likely the
photodissociation of H2O by the UV radiation generated in the terminal outflow
shock of HH211.Comment: ApJ Letters, in pres
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
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