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1.
P. F. Browne 《Astrophysics and Space Science》1995,233(1-2):329-336
At an early stage in the lives of stars and galaxies when they are surrounded by discs, vorticity in the disc concentrates into a central vortex, thus converting a Keplerian velocity fieldu
ø r
–1/2 into an irrotational velocity fieldu
ør
–1, which implies inward transfer of angular momentum. Centrifugal forces due to spin-up of the inner region and gravity dominant in the outer region then squeeze gas at intermediate layers, increasing pressure gradient in the axial direction sufficiently to drive a wide-angle low-velocity bipolar outflow from the disc. A logarithmic singularity of vorticity at the axis implies strong centrifugal forces which expand plasma to radiusR where pressure gradient balances centrifugal force density of ions; the much weaker centrifugal force density of electrons cannot balance pressure gradient, so that electrons are driven inwards relative to ions until charge separation limits the relative displacement. Now the radial gradient ofu
øcauses ions to rotate at a different rate to electrons, generating an azimuthal current densityj
øwhich is the source of an axial magnetic fieldB
zin the core of the central vortex. Centrifuging carries lines of B to the core wall, where they are wound into helical force-free configuration with B j. An annular channel of radiusR and thickness R into which parallel helical lines ofj andB are compressed constitutes a magnetic vortex tube (MVT). An MVT separates an inner high-velocity highly collimated outflow from the outer low-velocity wide-angle outflow, and is responsible for jets. Magnetic pinches in the MVT may constrict the core flow at HH objects. 相似文献
2.
Katsuo Ogura 《Astrophysics and Space Science》1995,224(1-2):151-154
Two pairs of giant (linear size 1 pc) bow shock structures have been discovered, each located symmetrically about HH 1/2 and HH 124. Their Herbig-Haro (HH) natures have been confirmed by narrow band CCD imaging on and off [SII] 6717/6731 and/or slit spectroscopy. Multiple bow shocks are known associated with a few HH objects such as HH 34, and are interpreted as evidence for recurrent outflow activity of the exciting sources. The giant bow shocks associated with HH 1/2 or HH 124 provide further, beautiful examples of this phenomenon and, with dynamical ages of nearly 20000 yr in both pairs, extend its timescale by more than an order of magnitude. 相似文献
3.
David J. Ampleford Andrea Ciardi Sergey V. Lebedev Simon N. Bland Simon C. Bott Jeremy P. Chittenden Gareth N. Hall Adam Frank Eric Blackman 《Astrophysics and Space Science》2007,307(1-3):29-34
We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The
use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly
more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length
of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime
similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet
and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium. 相似文献
4.
Kurt Liffman 《Astrophysics and Space Science》2007,311(1-3):69-74
We discuss the star-disk electric circuit for a young stellar object (YSO) and calculate the expected torques on the star
and the disk. We obtain the same disk magnetic field and star-disk torques as given by standard magnetohydrodynamic (MHD)
analysis. We show how a short circuit in the star-disk electric circuit may produce a magnetically-driven jet flow from the
inner edge of a disk surrounding a young star.
An unsteady bipolar jet flow is produced that flows perpendicular to the disk plane. Jet speeds of order hundreds of kilometers
per second are possible, while the outflow mass loss rate is proportional to the mass accretion rate and is a function of
the disk inner radius relative to the disk co-rotation radius. 相似文献
5.
Ph. Nicolaï V. T. Tikhonchuk A. Kasperczuk T. Pisarczyk S. Borodziuk K. Rohlena J. Ullschmied 《Astrophysics and Space Science》2007,307(1-3):87-91
Under suitable conditions on laser intensity, focal spot radius and atomic number a radiative jet was launched from a planar
target. This jet was produced using a relatively low energy laser pulse, below 500 J and it presents similarities with astrophysical
protostellar jets. It lasts more than 10 ns, extends over several millimeters, has velocity more than 500 km/s, the Mach number
more than 10 and the density above 1018 cm−3. The mechanism of jet formation was inferred from the dimensional analysis and hydrodynamic two-dimensional simulations.
It is related to the radiative cooling while the magnetic fields play a minor role.
PACS numbers: 98.38.Fs, 52.50.Jm, 95.30.Qd 相似文献
6.
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for
the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results
from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has
been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence
of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the
gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST
mission. 相似文献
7.
Colin R. Masson 《Astrophysics and Space Science》1995,224(1-2):99-108
In the 3 decades since winds from young stars were discovered, there have been many observations of bipolar molecular flows and ionized jets, and it has been recognized that outflows are intimately linked to star formation. Despite many observational clues and theoretical ideas, we still do not have a fully coherent picture of the outflow process. 相似文献
8.
D. J. Ampleford S. V. Lebedev A. Ciardi S. N. Bland S. C. Bott G. N. Hall N. Naz C. A. Jennings M. Sherlock J. P. Chittenden A. Frank E. Blackman 《Astrophysics and Space Science》2007,307(1-3):51-56
Collimated flows ejected from young stars are believed to play a vital role in the star formation process by extracting angular
momentum from the accretion disk. We discuss the first experiments to simulate rotating radiatively cooled, hypersonic jets
in the laboratory. A modification of the conical wire array $z$-pinch is used to introduce angular momentum into convergent
flows of plasma, a jet-forming standing shock and into the jet itself. The rotation of the jet is evident in laser imaging
through the presence of discrete filaments which trace the rotational history of the jet. The presence of angular momentum
results in a hollow density profile in both the standing conical shock and the jet. 相似文献
9.
T. Aigner J. Greiner M. Sommer O. R. Williams R. M. Kippen K. Hurley M. Boër M. Niel 《Astrophysics and Space Science》1995,231(1-2):165-168
This paper describes a comparison of observations of the HH 30 jet/counterjet system and theoretical models of jets propagating in a strongly stratified medium. We find that the observed westward bending of the HH 30 jet and counterjet can be explained as the result of a plane-parallel pressure stratification of the surrounding environment. This model predicts specific properties for the kinematics of the outflow, that could be straight-forwardly checked with future spectroscopic and proper motion studies of HH 30. 相似文献
10.
We present the first-ever simulations of non-ideal magnetohydrodynamical (MHD) stellar winds coupled with disc-driven jets
where the resistive and viscous accretion disc is self-consistently described. The transmagnetosonic, collimated MHD outflows
are investigated numerically using the VAC code. Our simulations show that the inner outflow is accelerated from the central
object hot corona thanks to both the thermal pressure and the Lorentz force. In our framework, the thermal acceleration is
sustained by the heating produced by the dissipated magnetic energy due to the turbulence. Conversely, the outflow launched
from the resistive accretion disc is mainly accelerated by the magneto-centrifugal force. We also show that when a dense inner
stellar wind occurs, the resulting disc-driven jet have a different structure, namely a magnetic structure where poloidal
magnetic field lines are more inclined because of the pressure caused by the stellar wind. This modification leads to both
an enhanced mass ejection rate in the disc-driven jet and a larger radial extension which is in better agreement with the
observations besides being more consistent. 相似文献