Astrophysical plasma

Abstract: The cooling functions for a plasma slab are investigated under equilibrium and nonequilibrium conditions, over a range of 10 4 -10 85 K and for a range of abundances Radiative transfer and diffuse field are calculated in the isobaric nonequilibrium models using a one-dimensional cooling flow model, and the plasma is not assumed to be optically thin to all radiation Limiting cases of the plasma diffuse field coupling are calculated, and the resulting cooling functions are presented Some functions are terminated before reaching 10 4 K when the internal photoionization halts the cooling The functions represent a self-consistent set of curves covering a wide grid of temperature and metallicities using recently published atomic data and processes

Abstract: New X-ray observatories (Chandra and XMM-Newton) are providing a wealth of high-resolution X-ray spectra in which hydrogen- and helium-like ions are usually strong features. We present results from a new collisional-radiative plasma code, the Astrophysical Plasma Emission Code (APEC), which uses atomic data in the companion Astrophysical Plasma Emission Database (APED) to calculate spectral models for hot plasmas. APED contains the requisite atomic data such as collisional and radiative rates, recombination cross sections, dielectronic recombination rates, and satellite line wavelengths. We compare the APEC results to other plasma codes for hydrogen- and helium-like diagnostics and test the sensitivity of our results to the number of levels included in the models. We find that dielectronic recombination with hydrogen-like ions into high (n = 6-10) principal quantum numbers affects some helium-like line ratios from low-lying (n = 2) transitions.

Abstract: New acoustic waves originating from a balance of dust particle inertia and plasma pressure are investigated. It is shown that these waves can propagate linearly as a normal mode in a dusty plasma, and non-linearly as supersonic solitons of either positive or negative electrostatic potential.

Abstract: The flow behind an interplanetary shock was analyzed through the use of magnetic field and plasma data from five spacecraft, with emphasis on the magnetic cloud identified by a characteristic variation of the latitude angle of the magnetic field. The size of the cloud was found to be about 0.5 AU in radial extent and greater than 30 deg in azimuthal extent, with its front boundary almost normal to the radial direction. Because the field direction of the magnetic cloud as it moved past the spacecraft was observed to rotate nearly parallel to a plane, it is thought that the field configuration of the cloud was essentially two-dimensional. These results further suggest that the lines of force in the magnetic cloud formed loops, but it could not be determined whether these loops were open or closed.

Abstract: Different types of photometric observations in the 1930s (Trumpler 1930; Stebbins et al 1 934; 1939) clearly showed that the dark "holes" in the Milky Way, observed by William Herschel almost 150 years earlier, were in fact re­ gions of heavy obscuration by cosmic dust. Continuing observations since then have established that dust is an almost ubiquitous component of the cosmic environment. Remote sensing of dust in the interstellar, circumstellar, inter­ planetary, circumplanetary, and cometary environments has, more recently been complemented by in-situ detections of the last three. Furthermore, the inference of the existence of very small grains (so-called VSGs with dimensions of 10100 A) in the interstellar medium (Puget & Leger 1989) as well as their in-situ detection in the environment of comet PlHalley (Sagdeev et al 1989) reinforces the reasonable expectation that the transition from gas to large dust particles in the cosmic environment is a continuous one through macromolecules, clusters, and VSGs. These dust grains are invariably immersed in ambient plasma and radiative environments. They must therefore be necessarily electrically charged and consequently coupled to the plasma through electric and magnetic fields, with the coupling becoming stronger as the grain size decreases. While any plasma containing such charged dust grains is often loosely referred to as a dusty plasma, there are different regimes characterized by the relative magnitudes of three characteristic length scales, namely the dust grain size a, the plasma Debye length AD, and the average intergrain distance d(� n;;1/3 , wherend is the dust number density). In general cosmic plasma en­ vironments that are contaminated by dust can be characterized by either of two conditions 1. a « AD < d or 2. a « d < AD. In the first case the dust may