219 research outputs found
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
The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2 emission
To investigate the disk formation and jet launch in protostars is crucial to
comprehend the earliest stages of star and planet formation. We aim to
constrain the properties of the molecular jet and the disk of the HH 212
protostellar system at unprecedented angular scales through ALMA observations
of sulfur-bearing molecules, SO 9(8)-8(7), SO 10(11)-10(10), SO2 8(2,6)-7(1,7).
SO 9(8)-8(7) and SO2 8(2,6)-7(1,7) show broad velocity profiles. At systemic
velocity they probe the circumstellar gas and the cavity walls. Going from low
to high blue-/red-shifted velocities the emission traces the wide-angle outflow
and the fast (~100-200 km/s) and collimated (~90 AU) molecular jet revealing
the inner knots with timescales <50 years. The jet transports a mass loss rate
>0.2-2e-6 Msun/yr, implying high ejection efficiency (>0.03-0.3). The SO and
SO2 abundances in the jet are ~1e-7-1e-6. SO 10(11)-10(10) emission is compact
and shows small-scale velocity gradients indicating that it originates partly
from the rotating disk previously seen in HCO+ and C17O, and partly from the
base of the jet. The disk mass is >0.002-0.013 Msun, and the SO abundance in
the disk is ~1e-8-1e-7. SO and SO2 are effective tracers of the molecular jet
in the inner few hundreds AU from the protostar. Their abundances indicate that
1% - 40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to
ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4
orders of magnitude larger than in evolved protoplanetary disks. This may be
due to an SO enhancement in the accretion shock at the envelope-disk interface
or in spiral shocks if the disk is partly gravitationally unstable.Comment: 13 pages, 10 figures, accepted for publication by A&
The Herschel HIFI water line survey in the low-mass proto-stellar outflow L1448
As part of the WISH (Water In Star-forming regions with Herschel) key
project, we report on the observations of several ortho- and para-H2O lines
performed with the HIFI instrument towards two bright shock spots (R4 and B2)
along the outflow driven by the L1448 low-mass proto-stellar system, located in
the Perseus cloud. These data are used to identify the physical conditions
giving rise to the H2O emission and infer any dependence with velocity. These
observations provide evidence that the observed water lines probe a warm
(T_kin~400-600 K) and very dense (n 10^6 - 10^7 cm^-3) gas, not traced by other
molecules, such as low-J CO and SiO, but rather traced by mid-IR H2 emission.
In particular, H2O shows strong differences with SiO in the excitation
conditions and in the line profiles in the two observed shocked positions,
pointing to chemical variations across the various velocity regimes and
chemical evolution in the different shock spots. Physical and kinematical
differences can be seen at the two shocked positions. At the R4 position, two
velocity components with different excitation can be distinguished, with the
component at higher velocity (R4-HV) being less extended and less dense than
the low velocity component (R4-LV). H2O column densities of about 2 10^13 and 4
10^14 cm^-2 have been derived for the R4-LV and the R4-HV components,
respectively. The conditions inferred for the B2 position are similar to those
of the R4-HV component, with H2O column density in the range 10^14 - 5 10^14
cm^-2, corresponding to H2O/H2 abundances in the range 0.5 - 1 10^-5. The
observed line ratios and the derived physical conditions seem to be more
consistent with excitation in a low velocity J-type shock with large
compression rather than in a stationary C-shock, although none of these
stationary models seems able to reproduce all the characteristics of the
observed emission.Comment: Accepted for publication in A&
Evidence of a SiO collimated outflow from a massive YSO in IRAS 17233-3606
Studies of molecular outflows in high-mass young stellar objects reveal important information about the formation process of massive stars. We therefore selected the close-by IRAS 17233–3606 massive star-forming region to perform SiO observations with the SMA interferometer in the (5−4) line and with the APEX single-dish telescope in the (5−4) and (8–7) transitions. In this paper, we present a study of one of the outflows in the region, OF1, which shows several properties similar to jets driven by low-mass protostars, such as HH211 and HH212. It is compact and collimated, and associated with extremely high velocity CO emission, and SiO emission at high velocities. We used a state-of-the-art shock model to constrain the pre-shock density and shock velocity of OF1. The model also allowed us to self-consistently estimate the mass of the OF1 outflow. The shock parameters inferred by the SiO modelling are comparable with those found for low-mass protostars, only with higher pre-shock density values, yielding an outflow mass in agreement with those obtained for molecular outflows driven by early B-type young stellar objects. Our study shows that it is possible to model the SiO emission in high-mass star-forming regions in the same way as for shocks from low-mass young stellar objects
Shock excitation of H in the James Webb Space Telescope era
(Abridged) H2 is the most abundant molecule in the Universe. Thanks to its
widely spaced energy levels, it predominantly lights up in warm gas, T > 100 K,
such as shocked regions, and it is one of the key targets of JWST observations.
These include shocks from protostellar outflows, all the way up to starburst
galaxies and AGN. Shock models are able to simulate H2 emission. We aim to
explore H2 excitation using such models, and to test over which parameter space
distinct signatures are produced in H2 emission. We present simulated H2
emission using the Paris-Durham shock code over an extensive grid of 14,000
plane-parallel stationary shock models, a large subset of which are exposed to
an external UV radiation field. The grid samples 6 input parameters: preshock
density, shock velocity, transverse magnetic field strength, UV radiation field
strength, cosmic-ray-ionization rate, and PAH abundance. Physical quantities,
such as temperature, density, and width, have been extracted along with H2
integrated line intensities. The strength of the transverse magnetic field, set
by the scaling factor, b, plays a key role in the excitation of H2. At low
values of b (<~ 0.3, J-type shocks), H2 excitation is dominated by
vibrationally excited lines; at higher values (b >~ 1, C-type shocks),
rotational lines dominate the spectrum for shocks with an external radiation
field comparable to (or lower than) the solar neighborhood. Shocks with b >= 1
can be spatially resolved with JWST for nearby objects. When the input kinetic
energy flux increases, the excitation and integrated intensity of H2 increases
similarly. An external UV field mainly serves to increase the excitation,
particularly for shocks where the input radiation energy is comparable to the
input kinetic energy flux. These results provide an overview of the energetic
reprocessing of input kinetic energy flux and the resulting H2 line emission.Comment: Published in A&
The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor
Molecular outflows powered by young protostars strongly affect the kinematics
and chemistry of the natal molecular cloud through strong shocks resulting in
substantial modifications of the abundance of several species. As part of the
"Chemical Herschel Surveys of Star forming regions" guaranteed time key
program, we aim at investigating the physical and chemical conditions of H20 in
the brightest shock region B1 of the L1157 molecular outflow. We observed
several ortho- and para-H2O transitions using HIFI and PACS instruments on
board Herschel, providing a detailed picture of the kinematics and spatial
distribution of the gas. We performed a LVG analysis to derive the physical
conditions of H2O shocked material, and ultimately obtain its abundance. We
detected 13 H2O lines probing a wide range of excitation conditions. PACS maps
reveal that H2O traces weak and extended emission associated with the outflow
identified also with HIFI in the o-H2O line at 556.9 GHz, and a compact (~10")
bright, higher-excitation region. The LVG analysis of H2O lines in the
bow-shock show the presence of two gas components with different excitation
conditions: a warm (Tkin~200-300 K) and dense (n(H2)~(1-3)x10^6 cm-3) component
with an assumed extent of 10" and a compact (~2"-5") and hot, tenuous
(Tkin~900-1400 K, n(H2)~10^3-10^4 cm-3) gas component, which is needed to
account for the line fluxes of high Eu transitions. The fractional abundance of
the warm and hot H2O gas components is estimated to be (0.7-2)x10^{-6} and
(1-3)x10^{-4}, respectively. Finally, we identified an additional component in
absorption in the HIFI spectra of H2O lines connecting with the ground state
level, probably arising from the photodesorption of icy mantles of a
water-enriched layer at the edges of the cloud.Comment: Accepted for publication in A&A. 12 pages, 9 figures, 4 table
Spitzer spectral line mapping of the HH211 outflow
Aims: We employ archival Spitzer slit-scan observations of the HH211 outflow
in order to investigate its warm gas content, assess the jet mass flux in the
form of H2 and probe for the existence of an embedded atomic jet. Methods:
Detected molecular and atomic lines are interpreted by means of emission line
diagnostics and an existing grid of molecular shock models. The physical
properties of the warm gas are compared against other molecular jet tracers and
to the results of a similar study towards the L1448-C outflow. Results: We have
detected and mapped the v=0-0 S(0) - S(7) H2 lines and fine-structure lines of
S, Fe+, and Si+. H2 is detected down to 5" from the source and is characterized
by a "cool" T~300K and a "warm" T~1000 K component, with an extinction Av ~ 8
mag. The amount of cool H2 towards the jet agrees with that estimated from CO
assuming fully molecular gas. The warm component is well fitted by C-type
shocks with a low beam filling factor ~ 0.01-0.04 and a mass-flux similar to
the cool H2. The fine-structure line emission arises from dense gas with
ionization fraction ~0.5 - 5 x 10e-3, suggestive of dissociative shocks. Line
ratios to sulfur indicate that iron and silicon are depleted compared to solar
abundances by a factor ~10-50. Conclusions: Spitzer spectral mapping
observations reveal for the first time a cool H component towards the CO
jet of HH211 consistent with the CO material being fully molecular and warm at
~ 300 K. The maps also reveal for the first time the existence of an embedded
atomic jet in the HH211 outflow that can be traced down to the central source
position. Its significant iron and silicon depletion excludes an origin from
within the dust sublimation zone around the protostar. The momentum-flux seems
insufficient to entrain the CO jet, although current uncertainties on jet speed
and shock conditions are too large for a definite conclusion.Comment: 13 pages, 10 figures, accepted for publication in A&
Shockingly low water abundances in Herschel / PACS observations of low-mass protostars in Perseus
Protostars interact with their surroundings through jets and winds impacting
on the envelope and creating shocks, but the nature of these shocks is still
poorly understood. Our aim is to survey far-infrared molecular line emission
from a uniform and significant sample of deeply-embedded low-mass young stellar
objects in order to characterize shocks and the possible role of ultraviolet
radiation in the immediate protostellar environment. Herschel/PACS spectral
maps of 22 objects in the Perseus molecular cloud were obtained as part of the
`William Herschel Line Legacy' survey. Line emission from HO, CO,
and OH is tested against shock models from the literature.
Observed line ratios are remarkably similar and do not show variations with
source physical parameters. Observations show good agreement with the shock
models when line ratios of the same species are compared. Ratios of various
HO lines provide a particularly good diagnostic of pre-shock gas
densities, cm, in agreement with typical
densities obtained from observations of the post-shock gas. The corresponding
shock velocities, obtained from comparison with CO line ratios, are above 20
km\,s. However, the observations consistently show one-to-two orders of
magnitude lower HO-to-CO and HO-to-OH line ratios
than predicted by the existing shock models.
The overestimated model HO fluxes are most likely caused by an
overabundance of HO in the models since the excitation is
well-reproduced. Illumination of the shocked material by ultraviolet photons
produced either in the star-disk system or, more locally, in the shock, would
decrease the HO abundances and reconcile the models with
observations. Detections of hot HO and strong OH lines support
this scenario.Comment: 28 pages, 12 figures, accepted to Astronomy & Astrophysic
A symbolic defence of animal magnetism: a copperplate engraving by Ludwig Richter as the frontispiece of the account of the somnambulist Auguste K. (1843)
Revisiting the shocks in BHR71: new observational constraints and H2O predictions for Herschel
During the formation of a star, material is ejected along powerful jets that
impact the ambient material. This outflow phenomenon plays an important role in
the regulation of star formation. Understanding the associated shocks and their
energetic effects is therefore essential to the study of star formation. We
present comparisons of shock models with observations of H and SiO emission
in the bipolar outflow BHR71, and predict water emission, under the basic
assumption that the emission regions of the considered species coincide, at the
resolution of currently available observations. New SiO observations from APEX
are presented, and combined with \textit{Spitzer} and ground-based observations
of H to constrain shock models. The shock regions associated with targeted
positions in the molecular outflow are studied by means of a 1D code that
generates models of the propagation of stationary shock waves, and
approximations to non-stationary ones. The SiO emission in the inner part of
the outflow is concentrated near the apex of the corresponding bow-shock that
is also seen in the pure rotational transitions of H. Simultaneous
modelling is possible for H and SiO and leads to constraints on the silicon
pre-shock distribution on the grain mantles and/or cores. The best-fitting
models are found to be of the non-stationary type, but the degeneracy of the
solutions is still large. Pre-shock densities of 10 and 10 cm
are investigated, and the associated best-model candidates have rather low
velocity (respectively, 20-30 and 10-15 km s) and are not older than
1000 years. We provide emission predictions for water, focusing on the
brightest transitions, to be observed with the PACS and HIFI instruments of the
\textit{Herschel} Telescope.Comment: 22 pages (12 text + 10 appendix), 8 figures, 8 tables (4 text + 4
appendix). Abstract has been amended to fullfill arxiv requirement
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