Initial Phase-space Density Research Articles

A Model of Satellite Microsignatures for Saturn

We model the time- and longitude-dependent charged particle absorption signatures caused by solid body absorbers, such as icy satellites, in Saturn's magnetosphere. The reduction in particle density caused by passage of such an absorber through a magnetic flux tube is calculated numerically. We then solve numerically for the time- and space-dependent distribution of particles in phase space assuming transport by radial diffusion and longitudinal particle drifts. The fully time- and longitude- averaged solution of the lossy radial diffusion equation is assumed to be the initial state, and the calculation is performed for up to a few complete satellite orbital periods. In this way, we obtain a numerical solution for the effects of particle absorption and transport during the most recent orbit(s) of the absorbing body around Saturn, while we approximate the result of all previous orbits of the absorber with the fully relaxed, steady state solution. We define “high” and “low” diffusion rates, depending on whether the diffusive fill-in of the absorption wake is fast or slow compared to the time before the satellite re-encounters its wake. For two cases, using parameters appropriate for the low energy charged particle (LECP) instruments on the Voyager spacecraft, we simulate count rate profiles where microsignatures have been observed. In the case of an ion microsignature near Enceladus, we cannot reproduce the data using radial diffusion rates inferred by other studies. For an electron microsignature very close to Tethys, we do find that the simulated count rate profile has a deep enough minimum that it could be detected by the Voyager instrument. In some cases, observed ion microsignatures are deeper than the maximum possible depth predicted by our model for a fresh absorption signature immediately downstream of a moon, assuming high diffusion. In the low diffusion case, our model predicts deeper signatures, sufficient to account for observed microsignatures. However, in that case, the fully relaxed solution contains dramatic changes in the initial phase space density and furthermore we would then expect microsignatures to be observed at every satelliteL-shell crossing, which is not the case.

The phase space density in elliptical galaxies

view Abstract Citations (124) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Phase Space Density in Elliptical Galaxies Carlberg, R. G. Abstract The phase space mass densities of the cores of elliptical galaxies are found to generally exceed the phase space mass densities in galactic disks. Since the phase space density can never increase in a collisionless process, these data argue against the lower luminosity (MB fainter than -22) ellipticals being normally formed from stellar disks. It does leave open the possibility that subsequent dissipation of a gas component could increase the core densities to the large values required. A series of one-dimensional gravitational experiments shows a small region in the core which retains the initial phase space density. However, the observable phase density in the core is conserved only if the initial system has large random velocities. Publication: The Astrophysical Journal Pub Date: November 1986 DOI: 10.1086/164711 Bibcode: 1986ApJ...310..593C Keywords: Elliptical Galaxies; Galactic Evolution; Galactic Structure; Space Density; Density Distribution; Luminosity; Many Body Problem; Astrophysics; GALAXIES: FORMATION; GALAXIES: NUCLEI; GALAXIES: STRUCTURE full text sources ADS |

Microscopic Approach to Kinetic Theory: Inhomogeneous Systems

The microscopic linearized Vlasov equation is solved in terms of a generalized inverse dielectric function ε−1(r, r′; t, t′) and the initial phase-space density fluctuation. This expression is then used to calculate the density autocorrelation function and to obtain a generalized kinetic equation for plasmas and gravitational gases. It is shown that many of the results for the inhomogeneous system have a close similarity to the corresponding results for homogeneous systems. In particular, the test-particle theory is exhibited and an expression is obtained for the phase-space density of the polarization cloud associated with a test particle.