359 research outputs found
Solving the excitation and chemical abundances in shocks: the case of HH1
We present deep spectroscopic (3600 - 24700 A) X-shooter observations of the
bright Herbig-Haro object HH1, one of the best laboratories to study the
chemical and physical modifications caused by protostellar shocks on the natal
cloud. We observe atomic fine structure lines, HI, and He, recombination lines
and H_2, ro-vibrational lines (more than 500 detections in total). Line
emission was analyzed by means of Non Local Thermal Equilibiurm codes to derive
the electron temperature and density, and, for the first time, we are able to
accurately probe different physical regimes behind a dissociative shock. We
find a temperature stratification in the range 4000 - 80000 K, and a
significant correlation between temperature and ionization energy. Two density
regimes are identified for the ionized gas, a more tenuous, spatially broad
component (density about 10^3 cm^-3), and a more compact component (density >
10^5 cm^-3) likely associated with the hottest gas. A further neutral component
is also evidenced, having temperature lass than 10000 K and density > 10^4
cm^-3. The gas fractional ionization was estimated solving the ionization
equilibrium equations of atoms detected in different ionization stages. We find
that neutral and fully ionized regions co-exist inside the shock. Also,
indications in favor of at least partially dissociative shock as the main
mechanism for molecular excitation are derived. Chemical abundances are
estimated for the majority of the detected species. On average, abundances of
non-refractory/refractory elements are lower than solar of about 0.15/0.5 dex.
This testifies the presence of dust inside the medium, with a depletion factor
of Iron of about 40%.Comment: Accepted by The Astrophysical Journa
Effects of long term application of compost and poultry manure on soil quality of citrus orchards in Southern Italy.
A six-year study was carried out in an organically managed orange orchard located in Sicily (Southern Italy) to assess the effect of compost and organic fertilizers utilisation on soil quality. Adopting a randomized-block experimental design with three replicates, four treatments were carried out. In treatments 1 and 2, two different composts (C1 from distillery by products and C2 from livestock wastes) were applied. The plots of treatment 3 were fertilized using dried poultry manure. The control treatment was fertilized with mineral/synthetic fertilizers. In order to verify the hypothesis that composts and organic fertilizers improve soil fertility, soil quality was evaluated by selecting dynamic soil parameters, as indicators linked to C and N cycles. Total organic C, total N, C/N ratio, humified fraction, isoelectric focusing (IEF) of extracted organic matter, microbial biomass C, potentially mineralisable N under anaerobic conditions, potenzially mineralizable C, C mineralization quotient and metabolic quotient were determined for each sample. Furthermore, the Comunity level Physiological Profile (by Biolog tecnique) was defined, calculating derived functional biodiversity and versatility indexes. Parameters related to IEF and potentially mineralizable C showed significant differences among the treatments. Moreover, total C, total N and humification parameters tended to increase, while no differences were observed in biodiversity indexes. On these findings, it was concluded that composts and poultry manure only weakly affected soil properties, though they increased soil nutritive elements potentially available to crops
Water in low-mass star-forming regions with Herschel (WISH-LM): High-velocity H2O bullets in L1448-MM observed with HIFI
Herschel-HIFI observations of water in the low-mass star-forming object
L1448-MM, known for its prominent outflow, are presented, as obtained within
the `Water in star-forming regions with Herschel' (WISH) key programme. Six
H2-16O lines are targeted and detected (E_up/k_B ~ 50-250 K), as is CO J= 10-9
(E_up/k_B ~ 305 K), and tentatively H2-18O 110-101 at 548 GHz. All lines show
strong emission in the "bullets" at |v| > 50 km/s from the source velocity, in
addition to a broad, central component and narrow absorption. The bullets are
seen much more prominently in HO than in CO with respect to the central
component, and show little variation with excitation in H2O profile shape.
Excitation conditions in the bullets derived from CO lines imply a temperature
>150 K and density >10^5 cm^-3, similar to that of the broad component. The
H2O/CO abundance ratio is similar in the "bullets" and the broad component, ~
0.05-1.0, in spite of their different origins in the molecular jet and the
interaction between the outflow and the envelope. The high H2O abundance
indicates that the bullets are H2 rich. The H2O cooling in the "bullets" and
the broad component is similar and higher than the CO cooling in the same
components. These data illustrate the power of Herschel-HIFI to disentangle
different dynamical components in low-mass star-forming objects and determine
their excitation and chemical conditions.Comment: Accepted for publication in A&
IR diagnostics of embedded jets: velocity resolved observations of the HH34 and HH1 jets
We present VLT-ISAAC medium resolution spectroscopy of the HH34 and HH1 jets.
Our aim is to derive the kinematics and the physical parameters and to study
how they vary with jet velocity. We use several important diagnostic lines such
as [FeII] 1.644um, 1.600um and H2 2.122um. In the inner jet region of HH34 we
find that both the atomic and molecular gas present two components at high and
low velocity. The [FeII] LVC in HH34 is detected up to large distances from the
source (>1000 AU), at variance with TTauri jets. In H2 2.122um, the LVC and HVC
are spatially separated. We detect, for the first time, the fainter red-shifted
counterpart down to the central source. In HH1, we trace the jet down to ~1"
from the VLA1 driving source: the kinematics of this inner region is again
characterised by the presence of two velocity components, one blue-shifted and
one red-shifted with respect to the source LSR velocity. In the inner HH34 jet
region, ne increases with decreasing velocity. Up to ~10" from the driving
source, and along the whole HH1 jet an opposite behaviour is observed instead,
with ne increasing with velocity. In both jets the mass flux is carried mainly
by the high-velocity gas. A comparison between the position velocity diagrams
and derived electron densities with models for MHD jet launching mechanisms has
been performed for HH34. While the kinematical characteristics of the line
emission at the jet base can be, at least qualitatively, reproduced by both
X-winds and disc-wind models, none of these models can explain the extent of
the LVC and the dependence of electron density with velocity that we observe.
It is possible that the LVC in HH34 represents gas not directly ejected in the
jet but instead denser ambient gas entrained by the high velocity collimated
jet.Comment: A&A accepte
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&
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&
Water emission from the chemically rich outflow L1157
In the framework of the Herschel-WISH key program, several ortho-H2O and
para-H2O emission lines, in the frequency range from 500 to 1700 GHz, were
observed with the HIFI instrument in two bow-shock regions (B2 and R) of the
L1157 cloud. The primary aim is to analyse water emission lines as a diagnostic
of the physical conditions in the blue (B2) and red-shifted (R) lobes to
compare the excitation conditions. A total of 5 ortho- and para-H216O plus one
o-H218O transitions were observed in B2 and R with a wide range of excitation
energies (27 K<=Eu<=215 K). The H2O spectra, observed in the two shocked
regions, show that the H2O profiles are markedly different in the two regions.
In particular, at the bow-shock R, we observed broad (~30 km s-1 with respect
to the ambient velocity) red-shifted wings where lines at different excitation
peak at different red-shifted velocities. The B2 spectra are associated with a
narrower velocity range (~6 km s-1), peaking at the systemic velocity. The
excitation analysis suggests, for B2, low values of column density NH2O
<=5{\times}1013 cm-2, a density range of 105 <=nH2 <=107 cm-3, and warm
temperatures (>=300 K). The presence of the broad red-shifted wings and
multiple peaks in the spectra of the R region, prompted the modelling of two
components. High velocities are associated with relatively low temperatures
(~100K),NH2O{\simeq}5{\times}1012-5{\times}1013 cm-2 and densities
nH2{\simeq}106-108 cm-3.Lower velocities are associated with higher excitation
conditions with Tkin>=300 K, very dense gas (nH2 ~108 cm-3) and low column
density (NH2O<5{\times}1013 cm-2).Comment: 9 pages, 8 figures, A&A in pres
Tracing the origins of permitted emission lines in RU Lupi down to AU scales
Most of the observed emission lines and continuum excess from young accreting
low mass stars (Classical T Tauri stars -- CTTSs) take place in the star-disk
or inner disk region. These regions have a complex emission topology still
largely unknown. In this paper the magnetospheric accretion and inner wind
contributions to the observed permitted He and H near infrared (NIR) lines of
the bright southern CTTS RU Lupi are investigated for the first time. Previous
optical observations of RU Lupi showed a large H-alpha profile, due to the
emission from a wind in the line wings, and a micro-jet detected in forbidden
lines. We extend this analysis to NIR lines through seeing-limited high
spectral resolution spectra taken with VLT/ISAAC, and adaptive optics (AO)
aided narrow-band imaging and low spectral resolution spectroscopy with
VLT/NACO. Using spectro-astrometric analysis we investigate the presence of
extended emission down to very low spatial scales (a few AU). The HeI 10830
line presents a P Cygni profile whose absorption feature indicates the presence
of an inner stellar wind. Moreover the spectro-astrometric analysis evidences
the presence of an extended emission superimposed to the absorption feature and
likely coming from the micro-jet detected in the optical. On the contrary, the
origin of the Hydrogen Paschen and Brackett lines is difficult to address. We
tried tentatively to explain the observed line profiles and flux ratios with
both accretion and wind models showing the limits of both approaches. The lack
of spectro-astrometric signal indicates that the HI emission is either compact
or symmetric. Our analysis confirms the sensitivity of the HeI line to the
presence of faint extended emission regions in the close proximity of the star.Comment: 11 pages, 4 figures, accepted for publication on A&
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High-J CO line emission from young stellar objects: from ISO to FIRST
we present the CO pure rotational spectrum at high J (Jup14) obtained with the Long Wavelength Spectrometer (LWS) on board of the ISO satellite towards molecular outflows exciting sources in nearby star formation regions. The physical conditions, derived using an LVG model for the line emission, indicate the presence of warm and dense gas, probably shock excited. The model fits show that often the bulk of this CO emission is expected in the spectral range that will be covered by FIRST, indicating the potentiality of this satellite to trace the warm component of gas emission in young stellar objects
Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data
We present a near-IR study of the EXor variable V1118 Ori, performed by
following a slightly declining phase after a recent outburst. In particular,
the near-IR (0.8 - 2.3 micron) spectrum, obtained for the first time, shows a
large variety of emission features of the HI and HeI recombination and CO
overtone. By comparing the observed spectrum with a wind model, a mass loss
rate value is derived along with other parameters whose values are typical of
an accreting T Tauri star. In addition, we have used X-ray data from the XMM
archive, taken in two different epochs during the declining phase monitored in
IR. X-ray emission (in the range 0.5 - 10 keV) permits to derive several
parameters which confirm the T Tauri nature of the source. In the near-IR the
object maintains a low visual extinction during all the activity phases,
confirming that variable extinction does not contribute to brightness
variations. The lack of both a significant amount of circumstellar material and
any evidence of IR cooling from collimated jet/outflow driven by the source,
indicates that, at least this member of the EXor class, is in a late stage of
the Pre-Main Sequence evolution. In the X-ray regime, an evident fading is
present, detected in the post-outburst phase, that cannot be reconciled with
the presence of any absorbing material. This circumstance, combined with the
persistence (in the pre- and post-outburst phases) of a temperature component
at about 10 MK, suggests that accretion has some influence in regulating the
coronal activity
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