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We investigated the proton enhancement and O6+/H depletion in the vicinity of the heliospheric current sheet (HCS) using data from STEREO/PLASTIC and STEREO/IMPACT. Three HCS crossing events were studied. For the first two events, the proton enhancement and O6+/H depletion are found to lie at one edge of the HCS. The proton density has a steep slope both at the HCS and at the other boundary of the enhancement. In the third event the proton enhancement and O6+/H depletion surround the HCS and last for 8 hours while the density profile is very different from the other two events. Velocity shear is observed at the HCS for the first two events but not for the third. The enhancement of hydrogen and depletion of oxygen at the streamer belt in the solar corona have been reported using UVCS observation. A potential connection with our observations is based on the similar features observed at 1 AU. How the plasma flows out of the streamer belt, and why there are different features in HCS encounters remain open questions for future study. [ABSTRACT FROM AUTHOR]

SERENA (‘Search for Exospheric Refilling and Emitted Natural Abundances’) is an instrument package that will fly on board the BepiColombo Mercury Planetary Orbiter (MPO); it will investigate the Mercury’s complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge-exchange processes, and by ionized particles originated through photo-ionization and again by surface release processes. In order to accomplish the scientific goals, in-situ analysis of the environmental elements is necessary, and for such a purpose the SERENA instrument shall include four units: two Neutral Particle Analyzers (ELENA and STROFIO) and two Ion Spectrometers (MIPA and PICAM). The scientific merit of SERENA is presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects. [ABSTRACT FROM AUTHOR]

We report observations of the neutral component of the solar wind from the Low Energy Neutral Atom (LENA) imager on the NASA IMAGE spacecraft from year 2001. There is a pronounced annual modulation of the neutral solar wind, and the flux outside of the upstream region is used to place an upper limit on the dust geometric cross section in the sunward direction at 1 AU of Γ1AU < 6×10-19 cm-1. This value agrees with inferences made from the zodiacal light. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Interstellar Pathfinder (ISP), our first step into the interstellar medium, is a scientific investigation to study the outer boundary of our heliosphere and the interstellar matter that flows into it. A wind of interstellar neutral gas penetrates to within several astronomical units (AU) of the Sun, giving us a direct sample of present-day galactic matter. ISP is a mission to this inner edge of the interstellar medium. Using highly sensitive instrumentation, ISP will determine the composition of our local interstellar environment. It will also take the first global images of the boundary region of the heliosphere at 100 to 150 AU. These measurements will allow ISP to answer fundamental questions about the origin of the solar system and the stars, about the evolution of our galaxy and of the universe, and about the characteristics of our local galactic environment and its influence on the heliosphere. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

This study examines the first direct measurements of the solar wind (SW) Ar/Ca elemental abundance ratio with the Mass Time-Of-Flight (MTOF) sensor of the Charge, Element, and Isotope Analysis System (CELIAS) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft. Two mass spectra are compiled for interstream (IS) associated SW and coronal hole (CH) associated SW. A detailed analysis of over 3.6 days of nonconsecutive IS associated SW speed (395 ± 25 km/s) places the Ar/Ca elemental ratio at 0.38±0.05. A similar analysis for CH associated SW speed (525 ± 25 km/s), with about 5.6 non-consecutive days of CH associated SW speed data, derived an Ar/Ca ratio of 0.59±0.07. The results of this study are consistent with most previously published Ar/Ca values from gradual solar energetic particle events and spectroscopy studies. [ABSTRACT FROM AUTHOR]

The MTOF sensor uses time of flight measurements in a harmonic potential region to identify elements and isotopes in the solar wind with excellent mass resolution. The combination of MTOF's large bandwidth electrostatic deflection system and the 3-axis stabilized orientation of SOHO results in excellent counting statistics. We report relative abundances of the iron isotopes with mass 54, 56 and 57 amu. Since these isotopes are chemically identical, we expect little fractionation either in the solar wind or in the instrument, resulting in relatively small estimated uncertainties. Our results agree, within the measurement uncertainties, with terrestrial values. [ABSTRACT FROM AUTHOR]

We present a study of the elemental composition of a sub-set of coronal mass ejections, namely events which have been identified of being of the magnetic cloud type (MC). We used plasma data from the MTOF sensor of the CELIAS instrument of the SOHO mission. So far we have investigated MCs of 1997 and 1998. The study covers the proton, alpha, and heavy ion elemental abundances. Considerable variations from event to event exist with regard to the density of the individual species with respect to regular "slow" solar wind preceding the MC plasma. However, two general features are observed. First, for the heavy elements (carbon through iron), which can be regarded as tracers in the solar wind plasma, a mass-dependent enrichment of ions monotonically increasing with mass is observed. The enrichment can be explained by a previously published theoretical model assuming coronal plasma loops on the solar surface being the precursor structure of the MC. Second, when comparing the MC plasma to regular solar wind composition, a net depletion of the lighter ions, helium through oxygen, is always observed. Proton and alpha particle abundances have to be regarded separately since they represent the main plasma. [ABSTRACT FROM AUTHOR]

Coronal elemental abundances, as compared with abundances in the solar wind and solar energetic particles, provide the means for connecting solar wind gas with its coronal source. Comparison of coronal abundances with photospheric values shows fractionation with the ionization potential of the atom, providing important, though not yet fully understood, information about the exchange of material between corona and chromosphere. Fractionation due to gravitational settling provides clues about flows within the corona. In this paper, we discuss the uncertainties of abundance determinations with spectroscopic techniques and in situ measurements, we survey the ranges of abundance variations in both the corona and solar wind, and we discuss the progress in correlating solar wind features with their coronal sources. [ABSTRACT FROM AUTHOR]

Chromium and iron are two heavy elements in the solar wind with similar masses. The MTOF (Mass Time Of Flight) sensor of the CELIAS investigation on the SOHO spacecraft easily allows these two elements to be resolved from one another. Taking the ratio of the densities of these two elements — as opposed to considering their absolute abundances — minimizes the effects of uncertainties in instrument efficiency. Measurements of the abundance ratio are presented here. The First Ionization Potential (FIP) of chromium is 6.76 eV, while the FIP of iron is 7.87 eV. Since Cr and Fe have similar FIPs the ratio of their abundances should not be biased by the FIP effect which is well known in different solar wind flows. Therefore the Cr/Fe ratio from the MTOF data should give a good measure of the photospheric abundance ratio. We also compare the ratio measured in this work to the meteoritic value. [ABSTRACT FROM AUTHOR]