8,594 research outputs found
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
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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
Electromagnetic transition form factors of negative parity nucleon resonances
We have calculated the transition form factors for the electromagnetic
excitation of the negative parity resonances of the nucleon using different
models previously proposed and we discuss their results and limits by
comparison with experimental data.Comment: 13 pages, 6 figures, to be published on Journal of Physics
[OI]63micron jets in class 0 sources detected by Herschel
We present Herschel PACS mapping observations of the [OI]63 micron line
towards protostellar outflows in the L1448, NGC1333-IRAS4, HH46, BHR71 and
VLA1623 star forming regions. We detect emission spatially resolved along the
outflow direction, which can be associated with a low excitation atomic jet. In
the L1448-C, HH46 IRS and BHR71 IRS1 outflows this emission is kinematically
resolved into blue- and red-shifted jet lobes, having radial velocities up to
200 km/s. In the L1448-C atomic jet the velocity increases with the distance
from the protostar, similarly to what observed in the SiO jet associated with
this source. This suggests that [OI] and molecular gas are kinematically
connected and that this latter could represent the colder cocoon of a jet at
higher excitation. Mass flux rates (\.M(OI)) have been measured from
the [OI]63micron luminosity adopting two independent methods. We find values in
the range 1-4 10 Mo/yr for all sources but HH46, for which an order of
magnitude higher value is estimated. \.M(OI) are compared with mass
accretion rates (\.M) onto the protostar and with \.M derived
from ground-based CO observations. \.M(OI)/\.M ratios are in
the range 0.05-0.5, similar to the values for more evolved sources.
\.M(OI) in HH46 IRS and IRAS4A are comparable to \.M(CO), while
those of the remaining sources are significantly lower than the corresponding
\.M(CO). We speculate that for these three sources most of the mass
flux is carried out by a molecular jet, while the warm atomic gas does not
significantly contribute to the dynamics of the system.Comment: 37 pages and 12 figures, accepted for publication on Astrophysical
Journa
Achievement goals, self-handicapping, and performance: A 2 × 2 achievement goal perspective
Elliot and colleagues (2006) examined the effects of experimentally induced achievement goals, proposed by the
trichotomous model, on self-handicapping and performance in physical education. Our study replicated and extended the
work of Elliot et al. by experimentally promoting all four goals proposed by the 262 model (Elliot & McGregor, 2001),
measuring the participants’ own situational achievement goals, using a relatively novel task, and testing the participants in a group setting. We used a randomized experimental design with four conditions that aimed to induce one of the four goals advanced by the 262 model. The participants (n¼138) were undergraduates who engaged in a dart-throwing task. The results pertaining to self-handicapping partly replicated Elliot and colleagues’ findings by showing that experimentally promoted performance-avoidance goals resulted in less practice. In contrast, the promotion of mastery-avoidance goals did
not result in less practice compared with either of the approach goals. Dart-throwing performance did not differ among the four goal conditions. Personal achievement goals did not moderate the effects of experimentally induced goals on selfhandicapping and performance. The extent to which mastery-avoidance goals are maladaptive is discussed, as well as the interplay between personal and experimentally induced goals
A combined optical/infrared spectral diagnostic analysis of the HH1 jet
Complete flux-calibrated spectra covering the spectral range from 6000 A to
2.5 um have been obtained along the HH1 jet and analysed in order to explore
the potential of a combined optical/near-IR diagnostic applied to jets from
young stellar objects. Important physical parameters have been derived along
the jet using various diagnostic line ratios. This multi-line analysis shows,
in each spatially unresolved knot, the presence of zones at different
excitation conditions, as expected from the cooling layers behind a shock
front. In particular, a density stratification in the jet is evident from
ratios of various lines of different critical density. In particular, [FeII]
lines originate in a cooling layer located at larger distances from the shock
front than that generating the optical lines, where the compression is higher
and the temperature is declining. The derived parameters were used to measure
the mass flux along the jet, adopting different procedures, the advantages and
limitations of which are discussed. dM/dt is high in the initial part of the
flow but decreases by about an order of magnitude further out. Conversely, the
mass flux associated with the warm molecular material is low and does not show
appreciable variations along the jet. We suggest that part of the mass flux in
the external regions is not revealed in optical and IR lines because it is
associated with a colder atomic component, which may be traced by the far-IR [O
I]63 um line.
Finally, we find that the gas-phase abundance of refractory species is lower
than the solar value suggesting that a significant fraction of dust grains may
still be present in the jet beam.Comment: Accepted on Astronomy & Astrophysic
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Strong H<sub>2</sub>O and high-<i>J</i> CO emission towards the Class 0 protostar L1448-mm
The spectrum of the Class 0 source L1448-mm has been measured over the wavelength range extending from 6 to 190 μm with the Long Wavelength Spectrometer (LWS) and the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). The far infrared spectrum is dominated by strong emission from gaseous H2O and from CO transitions with rotational quantum numbers J ≥ 14; in addition, the H2 pure rotational lines S(3), S(4) and S(5), the OH fundamental line at 119 μm, as well as emission from [O I]63 μm and [C II] 158 μm are also observed. The strong CO and water emission can be consistently explained as originating in a warm gas component at T ~ 700-1400 K and nH2~(3-50) 104cm-3 , which fills about 0.2-2% of the ~ 75" LWS field of view (corresponding, assuming a single emitting region, to a physical size of about (3-12)" or (0.5-2) 10-2 pc at d = 300 pc). We derive an H2O/CO abundance ratio ~ 5, which, assuming a standard CO/H2 abundance of 10-4, corresponds to H2O/H2 ~ 5 10-4. This value implies that water is enhanced by about a factor ~ 103 with respect to its expected abundance in the ambient gas. This is consistent with models of warm shocked regions which predict that most of the free atomic oxygen will be rapidly converted into water once the temperature of the post-shocked gas exceeds ~ 300 K. The relatively high density and compact size inferred for this emission may suggest an origin in the shocked region along the molecular jet traced by SiO and EHV CO millimeter line emission. Further support is given by the fact that the observed enhancement in H2O can be explained by shock conditions similar to those expected to produce the abundant SiO observed in the region. L1448-mm shows the largest water abundance so far observed by ISO amongst young sources displaying outflow activity; we argue that the occurrence of multiple shocks over a relatively short interval of time, like that evidenced in the surroundings of L1448-mm, could have contributed to enrich the molecular jet with a high H2O column density
Reversible melting and equilibrium phase formation of (Bi,Pb)2Sr2Ca2Cu3O10+d
The decomposition and the reformation of the (Bi,Pb)2Sr2Ca2Cu3O10+d
(?Bi,Pb(2223)?) phase have been investigated in-situ by means of
High-Temperature Neutron Diffraction, both in sintered bulk samples and in
Ag-sheathed monofilamentary tapes. Several decomposition experiments were
performed at various temperatures and under various annealing atmospheres,
under flowing gas as well as in sealed tubes, in order to study the appropriate
conditions for Bi,Pb(2223) formation from the melt. The Bi,Pb(2223) phase was
found to melt incongruently into (Ca,Sr)2CuO3, (Sr,Ca)14Cu24O41 and a
Pb,Bi-rich liquid phase. Phase reformation after melting was successfully
obtained both in bulk samples and Ag-sheathed tapes. The possibility of
crystallising the Bi,Pb(2223) phase from the melt was found to be extremely
sensitive to the temperature and strongly dependent on the Pb losses. The study
of the mass losses due to Pb evaporation was complemented by thermogravimetric
analysis which proved that Pb losses are responsible for moving away from
equilibrium and therefore hinder the reformation of the Bi,Pb(2223) phase from
the melt. Thanks to the full pattern profile refinement, a quantitative phase
analysis was carried out as a function of time and temperature and the role of
the secondary phases was investigated. Lattice distortions and/or transitions
were found to occur at high temperature in Bi,Pb(2223), Bi,Pb(2212),
(Ca,Sr)2CuO3 and (Sr,Ca)14Cu24O41, due to cation diffusion and stoichiometry
changes. The results indicate that it is possible to form the Bi,Pb(2223) phase
from a liquid close to equilibrium conditions, like Bi(2212) and Bi(2201), and
open new unexplored perspectives for high-quality Ag-sheathed Bi,Pb(2223) tape
processing.Comment: 45 pages (including references,figures and captions), 13 figures
Submitted to Supercond. Sci. Techno
OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS
OH is a key species in the water chemistry of star-forming regions, because
its presence is tightly related to the formation and destruction of water. This
paper presents OH observations from 23 low- and intermediate-mass young stellar
objects obtained with the PACS integral field spectrometer on-board Herschel in
the context of the Water In Star-forming Regions with Herschel (WISH) key
program. Most low-mass sources have compact OH emission (< 5000 AU scale),
whereas the OH lines in most intermediate-mass sources are extended over the
whole PACS detector field-of-view (> 20000 AU). The strength of the OH emission
is correlated with various source properties such as the bolometric luminosity
and the envelope mass, but also with the OI and H2O emission. Rotational
diagrams for sources with many OH lines show that the level populations of OH
can be approximated by a Boltzmann distribution with an excitation temperature
at around 70 K. Radiative transfer models of spherically symmetric envelopes
cannot reproduce the OH emission fluxes nor their broad line widths, strongly
suggesting an outflow origin. Slab excitation models indicate that the observed
excitation temperature can either be reached if the OH molecules are exposed to
a strong far-infrared continuum radiation field or if the gas temperature and
density are sufficiently high. Using realistic source parameters and radiation
fields, it is shown for the case of Ser SMM1 that radiative pumping plays an
important role in transitions arising from upper level energies higher than 300
K. The compact emission in the low-mass sources and the required presence of a
strong radiation field and/or a high density to excite the OH molecules points
towards an origin in shocks in the inner envelope close to the protostar.Comment: Accepted for publication in Astronomy and Astrophysics. Abstract
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