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1.
Observations and measurements in the solar wind, the Jovian atmosphere and the gases trapped in lunar surface material provide
the main evidence from which the isotopic composition of H, He and Ne in the Protosolar Cloud (PSC) is derived. These measurements
and observations are reviewed and the corrections are discussed that are needed for obtaining from them the PSC isotopic ratios.
The D/H, 3He/4He (D+3He)/H, 20Ne/22Ne and 21Ne/22Ne ratios adopted for the PSC are presented. Protosolar abundances provide the basis for the interpretation of isotopic ratios
measured in the various solar system objects. In this article we discuss constraints derived from the PSC abundances on solar
mixing, the origin of atmospheric neon, and the nature of the “SEP” component of neon trapped at the lunar surface. We also
discuss constraints on the galactic evolution provided by the isotopic abundances of H and He in the PSC.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
R. C. Wiens D. S. Burnett C. M. Hohenberg A. Meshik V. Heber A. Grimberg R. Wieler D. B. Reisenfeld 《Space Science Reviews》2007,130(1-4):161-171
The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition,
particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the
solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal
hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing
due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives
will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different
solar-wind regimes, and 15N/14N and 18O/17O/16O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind
and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation
between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere
and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed
system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which
in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped
in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being
measured. 相似文献
3.
The Sun is the largest reservoir of matter in the solar system, which formed 4.6 Gyr ago from the protosolar nebula. Data
from space missions and theoretical models indicate that the solar wind carries a nearly unfractionated sample of heavy isotopes
at energies of about 1 keV/amu from the Sun into interplanetary space. In anticipation of results from the Genesis mission’s
solar-wind implanted samples, we revisit solar wind isotopic abundance data from the high-resolution CELIAS/MTOF spectrometer
on board SOHO. In particular, we evaluate the isotopic abundance ratios 15N/14N, 17O/16O, and 18O/16O in the solar wind, which are reference values for isotopic fractionation processes during the formation of terrestrial planets
as well as for the Galactic chemical evolution. We also give isotopic abundance ratios for He, Ne, Ar, Mg, Si, Ca, and Fe
measured in situ in the solar wind. 相似文献
4.
V. S. Heber R. C. Wiens D. B. Reisenfeld J. H. Allton H. Baur D. S. Burnett C. T. Olinger U. Wiechert R. Wieler 《Space Science Reviews》2007,130(1-4):309-316
The concentrator on Genesis provided samples of increased fluences of solar wind ions for precise determination of the oxygen
isotopic composition. The concentration process caused mass fractionation as a function of the radial target position. This
fractionation was measured using Ne released by UV laser ablation and compared with modelled Ne data, obtained from ion-trajectory
simulations. Measured data show that the concentrator performed as expected and indicate a radially symmetric concentration
process. Measured concentration factors are up to ∼30 at the target centre. The total range of isotopic fractionation along
the target radius is 3.8%/amu, with monotonically decreasing 20Ne/22Ne towards the centre, which differs from model predictions. We discuss potential reasons and propose future attempts to overcome
these disagreements. 相似文献
5.
R. Wieler 《Space Science Reviews》1998,85(1-2):303-314
Lunar soil and certain meteorites contain noble gases trapped from the solar wind at various times in the past. The progress
in the last decade to decipher these precious archives of solar history is reviewed. The samples appear to contain two solar
noble gas components with different isotopic composition. The solar wind component resides very close to grain surfaces and
its isotopic composition is identical to that of present-day solar wind. Experimental evidence seems by now overwhelming that
somewhat deeper inside the grains there exists a second, isotopically heavier component. To explain the origin of this component
remains a challenge, because it is much too abundant to be readily reconciled with the known present day flux of solar particles
with energies above those of the solar wind. The isotopic composition of solar wind noble gases may have changed slightly
over the past few Ga, but such a change is not firmly established. The upper limit of ~5% per Ga for a secular increase of
the 3He/4He ratio sets stringent limits on the amount of He that may have been brought from the solar interior to the surface
(cf. Bochsler, 1992). Relative abundances of He, Ne, and Ar in present-day solar wind are the same as the long term average
recorded in metallic Fe grains in meteorites within error limits of some 15-20%. Xe, and to a lesser extent Kr, are enriched
in the solar wind similar to elements with a first ionisation potential < 10 eV, although Kr and Xe have higher FIPs. This
can be explained if the ionisation time governs the FIP effect (Geiss and Bochsler, 1986).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
7.
The solar wind charge state and elemental compositions have been measured with the Solar Wind Ion Composition Spectrometers
(SWICS) on Ulysses and ACE for a combined period of about 25 years. This most extensive data set includes all varieties of
solar wind flows and extends over more than one solar cycle. With SWICS the abundances of all charge states of He, C, N, O,
Ne, Mg, Si, S, Ar and Fe can be reliably determined (when averaged over sufficiently long time periods) under any solar wind
flow conditions. Here we report on results of our detailed analysis of the elemental composition and ionization states of
the most unbiased solar wind from the polar coronal holes during solar minimum in 1994–1996, which includes new values for
the abundance S, Ca and Ar and a more accurate determination of the 20Ne abundance. We find that in the solar minimum polar coronal hole solar wind the average freezing-in temperature is ∼1.1×106 K, increasing slightly with the mass of the ion. Using an extrapolation method we derive photospheric abundances from solar
wind composition measurements. We suggest that our solar-wind-derived values should be used for the photospheric ratios of
Ne/Fe=1.26±0.28 and Ar/Fe=0.030±0.007. 相似文献
8.
G. Gloeckler H. Balsiger A. Bürgi P. Bochsler L. A. Fisk A. B. Galvin J. Geiss F. Gliem D. C. Hamilton T. E. Holzer D. Hovestadt F. M. Ipavich E. Kirsch R. A. Lundgren K. W. Ogilvie R. B. Sheldon B. Wilken 《Space Science Reviews》1995,71(1-4):79-124
The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms–1 (protons) to 1280 kms–1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium. 相似文献
9.
Nordholt Jane E. Wiens Roger C. Abeyta Rudy A. Baldonado Juan R. Burnett Donald S. Casey Patrick Everett Daniel T. Kroesche Joseph Lockhart Walter L. MacNeal Paul McComas David J. Mietz Donald E. Moses Ronald W. Neugebauer Marcia Poths Jane Reisenfeld Daniel B. Storms Steven A. Urdiales Carlos 《Space Science Reviews》2003,105(3-4):561-599
The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios
that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include 17O/16O and 18O/16O to ±0.1%, 15N/14N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved
without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for
analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor
of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high
voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and
applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent
parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements
of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize
the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements
from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument
testing and handling.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Burnett D.S. Barraclough B.L. Bennett R. Neugebauer M. Oldham L.P. Sasaki C.N. Sevilla D. Smith N. Stansbery E. Sweetnam D. Wiens R.C. 《Space Science Reviews》2003,105(3-4):509-534
The Genesis Discovery mission will return samples of solar matter for analysis of isotopic and elemental compositions in terrestrial
laboratories. This is accomplished by exposing ultra-pure materials to the solar wind at the L1 Lagrangian point and returning
the materials to Earth. Solar wind collection will continue until April 2004 with Earth return in Sept. 2004. The general
science objectives of Genesis are to (1) to obtain solar isotopic abundances to the level of precision required for the interpretation
of planetary science data, (2) to significantly improve knowledge of solar elemental abundances, (3) to measure the composition
of the different solar wind regimes, and (4) to provide a reservoir of solar matter to serve the needs of planetary science
in the 21st century. The Genesis flight system is a sun-pointed spinner, consisting of a spacecraft deck and a sample return
capsule (SRC). The SRC houses a canister which contains the collector materials. The lid of the SRC and a cover to the canister
were opened to begin solar wind collection on November 30, 2001. To obtain samples of O and N ions of higher fluence relative
to background levels in the target materials, an electrostatic mirror (‘concentrator’) is used which focuses the incoming
ions over a diameter of about 20 cm onto a 6 cm diameter set of target materials. Solar wind electron and ion monitors (electrostatic
analyzers) determine the solar wind regime present at the spacecraft and control the deployment of separate arrays of collector
materials to provide the independent regime samples.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
W. R. Binns M. E. Wiedenbeck M. Arnould A. C. Cummings G. A. de Nolfo S. Goriely M. H. Israel R. A. Leske R. A. Mewaldt G. Meynet L. M. Scott E. C. Stone T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):439-449
We have measured the isotopic abundances of neon and a number of other species in the galactic cosmic rays (GCRs) using the
Cosmic Ray Isotope Spectrometer (CRIS) aboard the ACE spacecraft. Our data are compared to recent results from two-component
(Wolf–Rayet material plus solar-like mixtures) Wolf–Rayet (WR) models. The three largest deviations of galactic cosmic ray
isotope ratios from solar-system ratios predicted by these models, 12C/16O, 22Ne/20Ne, and 58Fe/56Fe, are very close to those observed. All of the isotopic ratios that we have measured are consistent with a GCR source consisting
of ∼20% of WR material mixed with ∼80% material with solar-system composition. Since WR stars are evolutionary products of
OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of our data with WR models
suggests that OB associations within superbubbles are the likely source of at least a substantial fraction of GCRs. In previous
work it has been shown that the primary 59Ni (which decays only by electron-capture) in GCRs has decayed, indicating a time interval between nucleosynthesis and acceleration
of >105 y. It has been suggested that in the OB association environment, ejecta from supernovae might be accelerated by the high
velocity WR winds on a time scale that is short compared to the half-life of 59Ni. Thus the 59Ni might not have time to decay and this would cast doubt upon the OB association origin of cosmic rays. In this paper we
suggest a scenario that should allow much of the 59Ni to decay in the OB association environment and conclude that the hypothesis of the OB association origin of cosmic rays
appears to be viable. 相似文献
12.
Roger C. Wiens Daniel B. Reisenfeld Chad Olinger Peter Wurz Veronika S. Heber Donald S. Burnett 《Space Science Reviews》2013,175(1-4):93-124
The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with measured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind velocity and angular distributions measured in flight, and predict fractionation patterns for various elements and isotopes of interest. A tighter angular distribution, mostly due to better spacecraft spin stability than assumed in pre-flight modeling, results in a steeper isotopic fractionation gradient between the center and the perimeter of the targets. Using the distribution of solar-wind velocities encountered during flight, which are higher than those used in pre-flight modeling, results in elemental abundance patterns slightly less peaked at the center. Mean fractionations trend with atomic mass, with differences relative to the measured isotopes of neon of +4.1±0.9 ‰/amu for Li, between ?0.4 and +2.8 ‰/amu for C, +1.9±0.7‰/amu for N, +1.3±0.4 ‰/amu for O, ?7.5±0.4 ‰/amu for Mg, ?8.9±0.6 ‰/amu for Si, and ?22.0±0.7 ‰/amu for S (uncertainties reflect Monte Carlo statistics). The slopes of the fractionation trends depend to first order only on the relative differential mass ratio, Δm/m. This article and a companion paper (Reisenfeld et al. 2012, this issue) provide post-flight information necessary for the analysis of the Genesis solar wind samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003). 相似文献
13.
R. Karrer P. Bochsler C. Giammanco F. M. Ipavich J. A. Paquette P. Wurz 《Space Science Reviews》2007,130(1-4):317-321
Using the Mass Time-of-Flight Spectrometer (MTOF)—part of the Charge, Elements, Isotope Analysis System (CELIAS)—onboard the
Solar Heliospheric Observatory (SOHO) spacecraft, we derive the nickel isotopic composition for the isotopes with mass 58,
60 and 62 in the solar wind. In addition we measure the elemental abundance ratio of nickel to iron. We use data accumulated
during ten years of SOHO operation to get sufficiently high counting statistics and compare periods of different solar wind
velocities. We compare our values with the meteoritic ratios, which are believed to be a reliable reference for the solar
system and also for the solar outer convective zone, since neither element is volatile and no isotopic fractionation is expected
in meteorites. Meteoritic isotopic abundances agree with the terrestrial values and can thus be considered to be a reliable
reference for the solar isotopic composition. The measurements show that the solar wind elemental Ni/Fe-ratio and the isotopic
composition of solar wind nickel are consistent with the meteoritic values. This supports the concept that low-FIP elements
are fed without relative fractionation into the solar wind. Our result also confirms the absence of substantial isotopic fractionation
processes for medium and heavy ions acting in the solar wind. 相似文献
14.
Johannes Geiss is a world leader and foremost expert on measurements and interpretation of the composition of matter that
reveals the history, present state, and future of astronomical objects. With his Swiss team he was first to measure the composition
of the noble gases in the solar wind when in the late 1960s he flew the brilliant solar wind collecting foil experiments on
the five Apollo missions to the moon. Always at the forefront of the art of composition measurements, he with his colleagues
determined the isotopic and elemental composition of the solar wind using instruments characterized by innovative design that
have provided the most comprehensive record of the solar wind composition under all solar wind conditions at all helio-latitudes.
He discovered heavy interstellar pickup ions, from which the composition of the neutral gas of the Local Interstellar Cloud
is determined, and the “Inner Source” of pickup ions. Johannes Geiss played a key role both in the in-situ measurements and
modeling of molecular ions in comets, and the interpretation of these data. He and co-workers measured the composition of
plasmas in the magnetospheres of Earth and Jupiter. Here we highlight Johannes Geiss’ many discoveries and seminal contributions
to our knowledge of the composition of matter of the Sun, solar wind, interstellar gas, early universe, comets and magnetospheres. 相似文献
15.
Barraclough B.L. Dors E.E. Abeyta R.A. Alexander J.F. Ameduri F.P. Baldonado J.R. Bame S.J. Casey P.J. Dirks G. Everett D.T. Gosling J.T. Grace K.M. Guerrero D.R. Kolar J.D. Kroesche J.L. Lockhart W.L. McComas D.J. Mietz D.E. Roese J. Sanders J. Steinberg J.T. Tokar R.L. Urdiales C. Wiens R.C. 《Space Science Reviews》2003,105(3-4):627-660
The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3-dimensional plasma measurements of the solar
wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the
spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section
electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis
of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is
an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics
and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while
electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin
of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest,
with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times
per spin. Complete ion and electron energy spectra are measured every ∼ 2.5 min (four spins of the spacecraft) with adequate
energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma
measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but
they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other
solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Daniel B. Reisenfeld Roger C. Wiens Bruce L. Barraclough John T. Steinberg Marcia Neugebauer Jim Raines Thomas H. Zurbuchen 《Space Science Reviews》2013,175(1-4):125-164
We describe the Genesis mission solar-wind sample collection period and the solar wind conditions at the L1 point during this 2.3-year period. In order to relate the solar wind samples to solar composition, the conditions under which the samples were collected must be understood in the context of the long-term solar wind. We find that the state of the solar wind was typical of conditions over the past four solar cycles. However, Genesis spent a relatively large fraction of the time in coronal-hole flow as compared to what might have been expected for the declining phase of the solar cycle. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) are used to determine the effectiveness of the Genesis solar-wind regime selection algorithm. The data collected by SWICS confirm that the Genesis algorithm successfully separated and collected solar wind regimes having distinct solar origins, particularly in the case of the coronal hole sample. The SWICS data also demonstrate that the different regimes are elementally fractionated. When compared with Ulysses composition data from the previous solar cycle, we find a similar degree of fractionation between regimes as well as fractionation relative to the average photospheric composition. The Genesis solar wind samples are under long-term curation at NASA Johnson Space Center so that as sample analysis techniques evolve, pristine solar wind samples will be available to the scientific community in the decades to come. This article and a companion paper (Wiens et al. 2013, this issue) provide post-flight information necessary for the analysis of the Genesis array and foil solar wind samples and the Genesis solar wind ion concentrator samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003). 相似文献
17.
R. A. Leske R. A. Mewaldt A. C. Cummings J. R. Cummings E. C. Stone T. T. Von Rosenvinge 《Space Science Reviews》1996,78(1-2):149-154
Measurements of the anomalous cosmic ray (ACR) isotopic composition have been made in three regions of the magnetosphere accessible from the polar Earth orbit of SAMPEX, including the interplanetary medium at high latitudes and geomagnetically trapped ACRs. At those latitudes where ACRs can penetrate the Earth's magnetic field while fully stripped galactic cosmic rays (GCRs) of similar energies are excluded, a pure ACR sample is observed to have the following composition: 15N/N < 0.023, 18O/16O < 0.0034, and 22Ne/20Ne = 0.077(+0.085, –0.023). We compare our values with those found by previous investigators and with those measured in other samples of solar and galactic material. In particular, a comparison of 22Ne/20Ne measurements from various sources implies that GCRs are not simply an accelerated sample of the local interstellar medium. 相似文献
18.
R. Kallenbach F.M. Ipavich H. Kucharek P. Bochsler A.B. Galvin J. Geiss F. Gliem G. Gloeckler H. Grünwaldt S. Hefti M. Hilchenbach D. Hovestadt 《Space Science Reviews》1998,85(1-2):357-370
Using the high-resolution mass spectrometer CELIAS/MTOF on board SOHO we have measured the solar wind isotope abundance ratios
of Si, Ne, and Mg and their variations in different solar wind regimes with bulk velocities ranging from 330 km/s to 650 km/s.
Data indicate a small systematic depletion of the heavier isotopes in the slow solar wind on the order of (1.4±1.3)% per amu
(2σ-error) compared to their abundances in the fast solar wind from coronal holes. These variations in the solar wind isotopic
composition represent a pure mass-dependent effect because the different isotopes of an element pass the inner corona with
the same charge state distribution. The influence of particle mass on the acceleration of minor solar wind ions is discussed
in the context of theoretical models and recent optical observations with other SOHO instruments.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
P. Bochsler 《Space Science Reviews》1998,85(1-2):291-302
The composition of the solar wind is largely determined by the composition of the source material, i.e. the present-day composition
of the outer convective zone. It is then modified by the processes which operate in the transition region and in the inner
corona. In situ measurements of the solar wind composition give a unique opportunity to obtain information on the isotopic
and elemental composition of the Sun. However, elemental — and to some degree also isotopic — fractionation can occur in the
flow of matter from the outer convective zone into the interplanetary space. The most important examples of elemental fractionation
are the well-known FIP/FIT effect (First Ionization Potential/Time) and the sometimes dramatic variations of the helium abundance
relative to hydrogen in the solar wind. A thorough investigation of fractionation processes which cause compositional variations
in different solar wind regimes is necessary to make inferences about the solar source composition from solar wind observations.
Our understanding of these processes is presently improving thanks to the detailed diagnostics offered by the optical instrumentation
on SOHO. Correlated observations of particle instruments on Ulysses, WIND, and SOHO, together with optical observations will
help to make inferences for the solar composition. Continuous in situ observations of several isotopic species with the particle
instruments on WIND and SOHO are currently incorporated into an experimental database to infer isotopic fractionation processes
which operate in different solar wind regimes between the solar surface and the interplanetary medium.
Except for the relatively minor effects of secular gravitational sedimentation which works at the boundary between the outer
convective zone and the radiative zone, refractory elements such as Mg can be used as faithful witnesses to monitor the magnitude
of these processes. With theoretical considerations it is possible to make inferences about the importance of isotopic fractionation
in the solar wind from a comparison of optical and in situ observations of elemental fractionation with the corresponding
models.
Theoretical models and preliminary results from particle observations indicate that the combined isotope effects do not exceed
a few percent per mass unit. In the worst case, which concerns the astrophysically important 3He/4He ratio, we expect an overall
effect of at most several percent in the sense of a systematic depletion of the heavier isotope. Continued observations with
WIND, SOHO, and ACE, and, with the revival of the foil technique, with the upcoming Genesis mission will further consolidate
our knowledge about the relation between solar wind dynamics and solar wind composition.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
M. I. Desai G. M. Mason R. E. Gold S. M. Krimigis C. M. S. Cohen R. A. Mewaldt J. E. Mazur J. R. Dwyer 《Space Science Reviews》2007,130(1-4):243-253
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged
∼0.1–60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results
show the following: (1) The Fe/O ratio decreases with increasing energy up to ∼10 MeV/nuc in ∼92% of the events and up to
∼60 MeV/nuc in ∼64% of the events. (2) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not
systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) Heavy ion abundances from C–Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in 3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks
in energizing particles up to ∼60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population
is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it
appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population
with a heavy ion enrichment pattern that is organized according to the ion’s mass-per-charge ratio. These new results indicate
that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor
to the CME shock acceleration process. 相似文献