1,189 research outputs found
Wide field CO J = 3->2 mapping of the Serpens Cloud Core
Context. Outflows provide indirect means to get an insight on diverse star
formation associated phenomena. On scales of individual protostellar cores,
outflows combined with intrinsic core properties can be used to study the mass
accretion/ejection process of heavily embedded protostellar sources. Methods.
An area comprising 460"x230" of the Serpens cloud core has been mapped in 12 CO
J = 3\to 2 with the HARP-B heterodyne array at the James Clerk Maxwell
Telescope; J = 3\to 2 observations are more sensitive tracers of hot outflow
gas than lower J CO transitions; combined with the high sensitivity of the
HARP-B receptors outflows are sharply outlined, enabling their association with
individual protostellar cores. Results. Most of ~20 observed outflows are found
to be associated with known protostellar sources in bipolar or unipolar
configurations. All but two outflow/core pairs in our sample tend to have a
projected orientation spanning roughly NW-SE. The overall momentum driven by
outflows in Serpens lies between 3.2 and 5.1 x 10^(-1) M\odot km s^(-1), the
kinetic energy from 4.3 to 6.7 x 10^(43) erg and momentum flux is between 2.8
and 4.4 x 10^(-4) M\odot km s^(-1) yr^(-1). Bolometric luminosities of
protostellar cores based on Spitzer photometry are found up to an order of
magnitude lower than previous estimations derived with IRAS/ISO data.
Conclusions. We confirm the validity of the existing correlations between the
momentum flux and bolometric luminosity of Class I sources for the homogenous
sample of Serpens, though we suggest that they should be revised by a shift to
lower luminosities. All protostars classified as Class 0 sources stand well
above the known Class I correlations, indicating a decline in momentum flux
between the two classes.Comment: 15 pages, 10 figures, accepted for publication in A&
Water cooling of shocks in protostellar outflows: Herschel-PACS map of L1157
Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H_2O emission with a spatial resolution comparable to ground based mm/sub-mm observations.
Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H_2O 179 μm transition obtained toward the young outflow L1157.
Methods. The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H_2O abundance and total cooling.
Results. Strong H_2O peaks are localized on both shocked emission knots and the central source position. The H_2O 179 μm emission is spatially correlated with emission from H_2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH_3. A strong H_2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H_2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H_2O abundance of the order of 10^(-4). This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H_2O cooling is ~10^(-1) L_☉, about 40% of the cooling due to H_2 and 23% of the total energy released in shocks along the L1157 outflow
Warm SiO gas in molecular bullets associated with protostellar outflows
In this paper we present the first SiO multiline analysis (from J=2-1 to
J=11-10) of the molecular bullets along the outflows of the Class 0 sources
L1448-mm and L1157-mm, obtained through observations with IRAM and JCMT. We
have computed the main physical parameters in each bullet and compared them
with other tracers of warm and dense gas and with models for the SiO excitation
in shocks. We find that the bullets close to L1448--mm, associated with high
velocity gas, have higher excitation conditions (n(H2) ~ 10^{6} cm^{-3}, T >
500 K) with respect to the L1157 bullets (n(H2) ~1-5 10^{5} cm^{-3}, T ~
100-300 K). In both the sources, there is a clear evidence of the presence of
velocity components having different excitation conditions, with the denser
and/or warmer gas associated with the gas at the higher speed. In L1448 the
bulk of the emission is due to the high-excitation and high velocity gas, while
in L1157 most of the emission comes from the low excitation gas at ambient
velocity. The observed velocity-averaged line ratios are well reproduced by
shocks with speeds v_s larger than ~ 30 km/s and densities ~ 10^{5} - 10^{6}
cm^{-3}. Plane-parallel shock models, however, fail to predict all the observed
line profiles and in particular the very similar profiles shown by both low and
high excitation lines. The overall observations support the idea that the L1157
clumps are shock interaction events older than the L1448 bullets close to the
driving source. In the latter objects, the velocity structure and the
variations of physical parameters with the velocity resemble very closely those
found in optical/IR jets near the protostar, suggesting that similar launching
and excitation mechanisms are also at the origin of collimated jets seen at
millimetre wavelengths.Comment: 11pages, 9 figures, A&A accepte
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&
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&
Searching for jet rotation in Class 0/I sources observed with GEMINI/GNIRS.
Original article can be found at: http://www.aanda.org/
Copyright The European Southern ObservatoryContext: In recent years, there has been a number of detections of gradients in the radial velocity profile across jets from young stars. The significance of these results is considerable. They may be interpreted as a signature of jet rotation about its symmetry axis, thereby representing the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. However, the possibility that we are indeed observing jet rotation in pre-main sequence systems is undergoing active debate.
Aims: To test the validity of a rotation argument, we must extend the survey to a larger sample, including younger sources.
Methods: We present the latest results of a radial velocity analysis on jets from Class 0 and I sources, using high resolution data from the infrared spectrograph GNIRS on GEMINI South. We obtained infrared spectra of protostellar jets HH 34, HH 111-H, HH 212 NK1 and SK1.
Results: The [Fe II] emission was unresolved in all cases and so Doppler shifts across the jet width could not be accessed. The H2 emission was resolved in all cases except HH 34. Doppler profiles across the molecular emission were obtained, and gradients in radial velocity of typically 3 km s-1 identified.
Conclusions: Agreement with previous studies implies they may be interpreted as jet rotation, leading to toroidal velocity and angular momentum flux estimates of 1.5 km s-1 and 1 × 10-5 yr-1 AU km s-1 respectively. However, caution is needed. For example, emission is asymmetric across the jets from HH 212 suggesting a more complex interpretation is warranted. Furthermore, observations for HH 212 and HH 111-H are conducted far from the source implying external influences are more likely to confuse the intrinsic flow kinematics. These observations demonstrate the difficulty of conducting this study from the ground, and highlight the necessity for high angular resolution via adaptive optics or space-based facilities
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&
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
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
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