Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session 4HE: Launching Dynamics for Stellar Jets |
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Sponsoring Units: HEDP HEDLA Chair: Patrick Hartigan, Rice University Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Promenade F |
Friday, April 11, 2008 4:20PM - 4:45PM |
4HE.00001: Generating Jets from Young Stars: An Observational Perspective Invited Speaker: Techniques, such as near-infrared interferometry, spectro-astrometry and high spatial resolution observations, both from the ground (e.g. with adaptive optics) and from space (e.g. from HST), are beginning to reveal conditions in the region where young stellar object jets are generated. Soon these will be augmented by high sensitivity radio observations from instruments such as e-MERLIN and EVLA. Because of their proximity and rich diagnostic line spectra, young stellar object jets are probably the best test-bed for MHD jet launching models. Here I review what high spatial resolutions tell us about jet parameters such as Mach number, plasma $\beta $, and angular momentum transport. In turn these can constrain the choice of parameters for realistic laboratory simulations of the generation of jets. [Preview Abstract] |
Friday, April 11, 2008 4:45PM - 5:10PM |
4HE.00002: Launching Mechanisms of Astrophysical Jets Invited Speaker: Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. However, extant proposals on how these structures may transfer angular momentum and energy from disks to jets through viscous or magnetic torques do not yet provide a full understanding of the physical mechanisms involved. Global stationary solutions do not permit an understanding of the stability of these structures; and global numerical simulations that include both the disk and jet physics are often limited to relatively short time scales and small (and possibly astrophysically unlikely) ranges of viscosity and resistivity parameters that are instead crucial to define the coupling of the inflow/outflow dynamics. Along these lines we discuss existing self-consistent time-dependent simulations of supersonic jets launched from magnetized accretion disks, using high resolution numerical techniques. In particular we concentrate on the effects of the disk physical parameters, and discuss under which conditions steady state solutions of the type proposed in the self-similar models of Blandford {\&} Payne can be reached and maintained in a self-consistent nonlinear stage. [Preview Abstract] |
Friday, April 11, 2008 5:10PM - 5:35PM |
4HE.00003: Laboratory-produced MHD plasma jets Invited Speaker: Because space plasmas are neither confined by vacuum chamber walls nor have magnetic fields produced by physical coils, space plasmas have shapes that are much less determinate than lab plasmas. An experimental program underway at Caltech produces plasmas where the shape is neither fixed by a vacuum chamber wall nor imposed by an external coil set, but rather is allowed to be determined by self-organizing MHD processes subject to the constraint of imposed boundary conditions analogous to the boundary conditions of space plasmas. These self-organizing processes are believed to be fundamental to astrophysical jets, solar coronal loops, and MHD turbulence (e.g. Taylor relaxation). The experimental dynamics are sufficiently reproducible to allow detailed study despite the morphology being complex and dynamic. A surprising result has been the observation that instead of the plasma uniformly filling up the available volume, the plasma is spatially localized in a highly collimated, small diameter magnetic flux tube, the length and axis of which change in time in response to MHD forces. A model shows that the collimation results from stagnation of linked magnetic flux frozen into a MHD-driven jet that accelerates plasma from the wall into the flux tube, filling the flux tube with plasma. Jet flow has been imaged with a high-speed multi-frame camera, diagnosed via Doppler spectroscopy, and most recently (i) the collision between two opposing, \textit{color-coded} jets flowing from opposite ends of a flux tube has been observed, and (ii) the collision of a jet with a target cloud has been observed. [Preview Abstract] |
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