344 research outputs found
An MHD study of SN 1006 and determination of the ambient magnetic field direction
In this work we employ an MHD numerical code to reproduce the morphology
observed for SN 1006 in radio synchrotron and thermal X-ray emission. We
introduce a density discontinuity, in the form of a flat cloud parallel to the
Galactic Plane, in order to explain the NW filament observed in optical
wavelengths and in thermal X-rays. We compare our models with observations. We
also perform a test that contrasts the radio emitting bright limbs of the SNR
against the central region, finding additional support to our results. Our main
conclusion is that the most probable direction of the ambient magnetic field is
on average perpendicular to the Galactic Plane.Comment: 7 pages, 5 figures, accepted by MNRA
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
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 Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física 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
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
The effect of a stellar magnetic variation on the jet velocity
Stellar jets are normally constituted by chains of knots with some
periodicity in their spatial distribution, corresponding to a variability of
order of several years in the ejection from the protostar/disk system. A widely
accepted theory for the presence of knots is related to the generation of
internal working surfaces due to variations in the jet ejection velocity. In
this paper we study the effect of variations in the inner disk-wind radius on
the jet ejection velocity. We show that a small variation in the inner
disk-wind radius produce a variation in the jet velocity large enough to
generate the observed knots. We also show that the variation in the inner
radius may be related to a variation of the stellar magnetic field.Comment: 5 pages, 3 figures, accepted for publication in Ap
A model of Mira's cometary head/tail entering the Local Bubble
We model the cometary structure around Mira as the interaction of an AGB wind
from Mira A, and a streaming environment. Our simulations introduce the
following new element: we assume that after 200 kyr of evolution in a dense
environment Mira entered the Local Bubble (low density coronal gas). As Mira
enters the bubble, the head of the comet expands quite rapidly, while the tail
remains well collimated for a 100 kyr timescale. The result is a
broad-head/narrow-tail structure that resembles the observed morphology of
Mira's comet. The simulations were carried out with our new adaptive grid code
WALICXE, which is described in detail.Comment: 12 pages, 8 figures (4 in color). Accepted for publication in The
Astrophysical Journa
Techno-economic evaluation of an ontology-based nurse call system via discrete event simulations
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