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A statistical analysis of interstellar He+ pickup ion measurements from SOHO/CTOF combined with magnetic field data from WIND/MFI enable quantitative study of wave-particle interactions in the inner heliosphere for the first time. Magnetic field vector measurements with a time resolu-tion of 3 seconds are used to determine power spectrum char-acteristics of interplanetary magnetic turbulence. These spec-tral characteristics are then compared in superposed epoch and correlation analyses with He+ fluxes and spectra. The observed pickup ion velocity distributions can be explained consistently as a consequence of pitch angle scattering of the interstellar pickup ions by Alfvenic fluctuations., Comment: 7 pages, 3 figures

We present a recent analysis with 1996 SOHO CELIAS CTOF data, which reveals correlations of He+ pickup ion fluxes and spectra with the magnetic field strength and solar wind density. The motivation is to better understand the ubiquitous large variations in both pickup ion fluxes and their velocity distributions found in interstellar pickup ion datasets. We concentrate on time periods of that can be associated with compression regions in the solar wind. Along with enhancements of the overall pickup ion fluxes, adiabatic heating and acceleration of the pickup ions are also observed in these regions. Transport processes that lead to the observed compressions and related heating or acceleration are discussed. A shift in velocity space associated with traveling interplanetary compression regions is observed, and a simple model presented to explain this phenomenon based on the conserved magnetic adiabatic moment., Comment: 4 pages, 5 figures, Solar Wind 10 Conference Proceedings Paper

A one dimensional sublimation model for cometary nuclei is used to derive size limits for the nuclei of sungrazing comets, and to estimate oxygen ion fluxes at 1 AU from their evaporation. Given that none of the ~300 sungrazers detected by the SOlar and Heliospheric Observatory (SOHO) was observed after disappearing behind the sun, and that small nuclei with a radius of ~3.5m could be observed, it is assumed that all SOHO sungrazers were completely destroyed. For the case that sublimation alone is sufficient for destruction, the model yields an upper size limit as a function of nuclear density, albedo and perihelion distance. If the density of the nuclei is that typical of porous ice (600kg/m^3), the maximum size is 63m. These results confirm similar model calculations by Weissman (1983). An analytical expression is derived that approximates the model results well. We discuss possible modifications of our results by different disruption mechanisms. While disruption by thermal stress does not change the upper size limits significantly, they may be somewhat increased by tidal disruption (up to 100m for a density of 600kg/m^3) dependent on the isotropy of the sublimation process and the tensile strength of the comet. Implications for the Kreutz family of sungrazers are discussed. Oxygen ions from the sublimation of sungrazing comets form a tail. Fluxes from this tail are sufficiently high to be measured at 1 AU by particle detectors on spacecraft, but the duration of a tail crossing is only about half an hour. Therefore the probability of a spacecraft actually encountering a tail of an evaporating sungrazer is only of the order of two percent per year., Comment: 32 pages, 11 figures, accepted for publication in Icarus

We present first results on the Ca isotopic abundances derived from the high resolution Mass Time-of-Flight (MTOF) spectrometer of the charge, element, and isotope analysis system (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO). We obtain isotopic ratios 40Ca/42Ca = (128+-47) and 40Ca/44Ca = (50+-8), consistent with terrestrial values. This is the first in situ determination of the solar wind calcium isotopic composition and is important for studies of stellar modeling and solar system formation since the present-day solar Ca isotopic abundances are unchanged from their original isotopic composition in the solar nebula., Comment: 14 pages, 3 figures

The observations by the ion composition instrument (ICI) on the ICE spacecraft made during the encounter with comet P/Giacobini-Zinner (Ogilvie et al., 1986) are discussed in detail. Solar wind He-4(2+) kinetic temperatures, densities, and velocities before, during, and after the encounter are presented. These data combined with He-4(2+) velocity distributions provide evidence for the existence of a thick diffuse shock. Relative abundances of water group ions and CO(+) are derived along with an estimate of the abundance of an ion with M/Q = 24 + or - 1 amu/e. The ICI data are compared with electron data from two other experiments (Bame et al., 1986; Meyer-Vernet et al., 1986) and found to be in reasonable agreement in the region outside the tail. Spectroscopic data for several neutral and ionic species are compared with the ICI results for the water group ions and CO(+). The spectroscopic data are also used to eliminate Mg(+) and CN(+) as candidates for the M/Q = 24 peak. The two most likely candidates are C2(+) and Na(+), but neither photoionization of parent neutrals nor sputtering from dust grains is sufficient to explain the observed abundance relative to H2O(+).

During the crossing of the ICE spacecraft through the coma of the comet Giacobini-Zinner, ions with a mass/charge ratio 24 + or - 1 were unexpectedly found. Na(+) and/or Mg(+) would fit into this mass range. Processes that could lead to high metal ion abundances in cometary comas are discussed and it is concluded that evaporation or sputtering from silicate grains are not likely to be responsible. A remaining possibility is the occurrence of alkali metals in the icy phase as a result of either cometary differentiation or cocondensation of these elements with the icy component prior to the accretion of cometary bodies.

The International Cometary Explorer spacecraft passed through the coma of comet Giacobini-Zinner about 7800 kilometers antisunward of the nucleus on September 11, 1985. The ion composition instrument was sensitive to ambient ions with mass-to-charge ratios in the ranges 1.4 to 3 atomic mass units per electron charge (amu/e) and 14 to 33 amu/e. Initial interpretation of the measurements indicates the presence of H2O(+), H3O(+), probably CO(+) and HCO(+), and ions in the mass range 23 to 24; possible candidates are Na(+) and Mg(+) and Mg(+). In addition to these heavy ions, measured over the velocity range 80 to 223 kilometers per second, the instruments measured He(2+) of solar wind origin over the range 237 to 463 kilometers per second. The heavy ions have a velocity distribution which indicates that they have been picked up by the motional electric field, whereas the light ions are steadily decelerated as the comet tail axis is approached. These results are in agreement with the picture of a comet primarily consisting of water ice, together with other material, that sublimes, streams away from the nucleus, becomes ionized, and interacts with the solar wind.