2,858 research outputs found
On the Influence of Magnetic Fields on the Structure of Protostellar Jets
We here present the first results of fully three-dimensional (3-D) MHD
simulations of radiative cooling pulsed (time-variable) jets for a set of
parameters which are suitable for protostellar outflows. Considering different
initial magnetic field topologies in approximate with the
thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which
permeating the jet and the ambient medium; and (iii) a purely toroidal field
permeating only the jet, we find that the overall morphology of the pulsed jet
is not very much affected by the presence of the different magnetic field
geometries in comparison to a nonmagnetic calculation. Instead, the magnetic
fields tend to affect essentially the detailed structure and emission
properties behind the shocks at the head and at the pulse-induced internal
knots, particularly for the helical and toroidal geometries. In these cases, we
find, for example, that the emissivity behind the internal knots can
be about three to four times larger than that of the purely hydrodynamical jet.
We also find that some features, like the nose cones that often develop at the
jet head in 2-D calculations involving toroidal magnetic fields, are smoothed
out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections
(for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar
Multidimensional Hydrodynamical Simulations of radiative cooling SNRs-clouds interactions: an application to Starburst Environments
In this work we are interested to study the by-products of SNR-clouds in a
starburst (SB) system. These interactions can have an important role in the
recycling of matter from the clouds to the ISM and vice-versa. In the present
work, we have focused our attention on the global effects of the interactions
between clouds and SN shock waves in the ISM of SB environments, and performed
3-D radiative cooling hydrodynamical simulations with the adaptive YGUAZU grid
code. We have also considered the effects of the photo-evaporation due to the
presence of a high number of UV photons from hot stars and supernovae (SNe).
The results have shown that, in the presence of radiative cooling, instead of
an efficient gas mixing with the diffuse ISM, the interactions cause the
fragmentation of the clouds into smaller ones. The results have also revealed
that the SNR-clouds interactions are less efficient at producing substantial
mass loss from the clouds to the diffuse ISM than mechanisms such as the
photo-evaporation caused by the UV flux from the hot stars.Comment: 15 pages, 25 figures. Figures with higher resolution at the page:
http://www.astro.iag.usp.br/~dalpino/ Astronomy & Astrophysics accepte
The precession of the giant HH34 outflow: a possible jet deceleration mechanism
The giant jets represent a fundamental trace of the historical evolution of
the outflow activity over timescales which are comparable to the accretion time
of the outflow sources in their main protostellar phase. The study of such huge
jets provides the possibility of retrieving important elements related to the
life of the outflow sources. In this paper, we study the role of precession
(combined with jet velocity-variability and the resulting enhanced interaction
with the surrounding environment) as a deceleration mechanism for giant jets
using a numerical approach. We obtain predictions of H alpha intensity maps and
position-velocity diagrams from 3D simulations of the giant HH 34 jet
(including an appropriate ejection velocity time-variability and a precession
of the outflow axis), and we compare them with previously published
observations of this object. Our simulations represent a step forward from
previous numerical studies of HH objects, in that the use of a 7-level, binary
adaptive grid has allowed us to compute models which appropiately cover all
relevant scales of a giant jet, from the ~ 100 AU jet radius close to the
source to the ~ 1 pc length of the outflow. A good qualitative and quantitative
agreement is found between the model predictions and the observations.
Moreover, we show that a critical parameter for obtaining a better or worse
agreement with the observations is the ratio rho_j/rho_a between the jet and
the environmental densities. The implications of this result in the context of
the current star formation models are discussed (ABRIDGED).Comment: 19 pages, 8 eps figs.,uses aaspp4; accepted by the Ap
Star formation triggered by SN explosions: an application to the stellar association of Pictoris
In the present study, considering the physical conditions that are relevant
in interactions between supernova remnants (SNRs) and dense molecular clouds
for triggering star formation we have built a diagram of SNR radius versus
cloud density in which the constraints above delineate a shaded zone where star
formation is allowed. We have also performed fully 3-D radiatively cooling
numerical simulations of the impact between SNRs and clouds under different
initial conditions in order to follow the initial steps of these interactions.
We determine the conditions that may lead either to cloud collapse and star
formation or to complete cloud destruction and find that the numerical results
are consistent with those of the SNR-cloud density diagram. Finally, we have
applied the results above to the Pictoris stellar association which is
composed of low mass Post-T Tauri stars with an age of 11 Myr. It has been
recently suggested that its formation could have been triggered by the shock
wave produced by a SN explosion localized at a distance of about 62 pc that may
have occurred either in the Lower Centaurus Crux (LCC) or in the Upper
Centaurus Lupus (UCL) which are both nearby older subgroups of that association
(Ortega and co-workers). Using the results of the analysis above we have shown
that the suggested origin for the young association at the proposed distance is
plausible only for a very restricted range of initial conditions for the parent
molecular cloud, i.e., a cloud with a radius of the order of 10 pc and density
of the order of 20 cm and a temperature of the order of 50100 K.Comment: 9 pages, 10 figures, to appear in MNRA
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