444 research outputs found
3D MHD simulation of polarized emission in SN 1006
We use three dimensional magnetohydrodynamic (MHD) simulations to model the
supernova remnant SN 1006. From our numerical results, we have carried out a
polarization study, obtaining synthetic maps of the polarized intensity, the
Stokes parameter , and the polar-referenced angle, which can be compared
with observational results. Synthetic maps were computed considering two
possible particle acceleration mechanisms: quasi-parallel and
quasi-perpendicular. The comparison of synthetic maps of the Stokes parameter
maps with observations proves to be a valuable tool to discern
unambiguously which mechanism is taking place in the remnant of SN 1006, giving
strong support to the quasi-parallel model.Comment: 6 pages, 4 figures, accepted by MNRA
Simulation of dark lanes in post--flare supra--arcades
Using two simulations of 1.5D, for the first time, in Costa et al. (2009) and
Shulz et al. (2010) we numerically reproduce the observational dark inflows
described in Verwichte et al. (2005). We show that the dark tracks can be
explained as hot plasma vacuums generated upstream of a slow magnetoacoustic
shock wave produced by a localized deposition of energy. In this work, we show
that the overall 2D results are in agreement with the observational behaviour.
However they show a slight shift in the characteristic parameter with respect
to those found previously. Also, we confirm qualitatively the behaviour found
in the previous papers, i.e. for a given numerical domain the period of the
kink--like structure is a function of the magnetic field intensity: larger
periods are associated with lower magnetic field intensities. Contrary to the
1D result -where the sunward dynamic is independent of the magnetic field
intensity due to its exclusively waveguide role- in the 2D simulation the
sunward speed is larger for larger values of the magnetic field. This can be
interpreted as the capability of the low coronal plasma to collimate the
deposition of energy into the magnetic field direction. The moving features
consistent of low--density and high--temperature plasma cavities have larger
inside values of the structuring parameter beta than the neighboring media.
Thus, the voids seem to be the emergence structures of a whole nonlinear
interacting plasma context of shocks and waves more than voided plasma loops
magnetically structured.Comment: 5 pages, 5 figure
Origin of the bilateral structure of the supernova remnant G296.5+10
In this work, we have modelled the supernova remnant (SNR) G296.5+10, by means of 3D magnetohydrodynamics (MHD) simulations. This remnant belongs to the bilateral SNR group and has an additional striking feature: the rotation measure (RM) in its eastern and western parts are very different. In order to explain both the morphology observed in radio-continuum and the RM, we consider that the remnant expands into a medium shaped by the superposition of the magnetic field of the progenitor star with a constant Galactic magnetic field. We have also carried out a polarization study from our MHD results, obtaining synthetic maps of the linearly polarized intensity and the Stokes parameters. This study reveals that both the radio morphology and the reported RM for G296.5+10 can be explained if the quasi-parallel acceleration mechanism is taking place in the shock front of this remnant.Fil: Moranchel-Basurto, A.. Universidad Nacional Autónoma de México; MéxicoFil: Velazquez, P.. Universidad Nacional Autónoma de México; MéxicoFil: Giacani, Elsa Beatriz. Universidad de Buenos Aires. Facultad de Arquitectura y Urbanismo; Argentina. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Toledo Roy, J. C.. Universidad Nacional Autónoma de México; MéxicoFil: Schneiter, E.. Universidad Nacional Autónoma de México; MéxicoFil: De Colle, F.. Universidad Nacional Autónoma de México; MéxicoFil: Esquivel, A.. Universidad Nacional Autónoma de México; Méxic
Tomographic reconstruction of the three-dimensional structure of the HH30 jet
The physical parameters of Herbig-Haro jets are usually determined from
emission line ratios, obtained from spectroscopy or narrow band imaging,
assuming that the emitting region is homogeneous along the line of sight. Under
the more general hypothesis of axisymmetry, we apply tomographic reconstruction
techniques to the analysis of Herbig-Haro jets. We use data of the HH30 jet
taken by Hartigan & Morse (2007) with the Hubble space telescope using the
slitless spectroscopy technique. Using a non-parametric Tikhonov regularization
technique, we determine the volumetric emission line intensities of the
[SII]6716,6731, [OI]6300 and [NII]6583 forbidden emission lines. From our
tomographic analysis of the corresponding line ratios, we produce
"three-dimensional" images of the physical parameters. The reconstructed
density, temperature and ionization fraction present much steeper profiles than
those inferred using the assumption of homogeneity. Our technique reveals that
the reconstructed jet is much more collimated than the observed one close to
the source (a width ~ 5 AU vs. ~ 20 AU at a distance of 10 AU from the star),
while they have similar widths at larger distances. In addition, our results
show a much more fragmented and irregular jet structure than the classical
analysis, suggesting that the the ejection history of the jet from the
star-disk system has a shorter timescale component (~ some months) superimposed
on a longer, previously observed timescale (of a few years). Finally, we
discuss the possible application of the same technique to other stellar jets
and planetary nebulae.Comment: 13 pages, 9 figures, accepted by Ap
Single-bubble and multi-bubble cavitation in water triggered by laser-driven focusing shock waves
In this study a single laser pulse spatially shaped into a ring is focused
into a thin water layer, creating an annular cavitation bubble and cylindrical
shock waves: an outer shock that diverges away from the excitation laser ring
and an inner shock that focuses towards the center. A few nanoseconds after the
converging shock reaches the focus and diverges away from the center, a single
bubble nucleates at the center. The inner diverging shock then reaches the
surface of the annular laser-induced bubble and reflects at the boundary,
initiating nucleation of a tertiary bubble cloud. In the present experiments,
we have performed time-resolved imaging of shock propagation and bubble wall
motion. Our experimental observations of single-bubble cavitation and collapse
and appearance of ring-shaped bubble clouds are consistent with our numerical
simulations that solve a one dimensional Euler equation in cylindrical
coordinates. The numerical results agree qualitatively with the experimental
observations of the appearance and growth of bubble clouds at the smallest
laser excitation rings. Our technique of shock-driven bubble cavitation opens
novel perspectives for the investigation of shock-induced single-bubble or
multi-bubble cavitation phenomena in thin liquids
A latitude-dependent wind model for Mira's cometary head
We present a 3D numerical simulation of the recently discovered cometary
structure produced as Mira travels through the galactic ISM. In our simulation,
we consider that Mira ejects a steady, latitude-dependent wind, which interacts
with a homogeneous, streaming environment. The axisymmetry of the problem is
broken by the lack of alignment between the direction of the relative motion of
the environment and the polar axis of the latitude-dependent wind. With this
model, we are able to produce a cometary head with a ``double bow shock'' which
agrees well with the structure of the head of Mira's comet. We therefore
conclude that a time-dependence in the ejected wind is not required for
reproducing the observed double bow shock.Comment: 4 pages, 4 figures, accepted for publication in ApJ
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