Papers by Stamatios Krimigis
Experimental Astronomy, 2009
... neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, ... more ... neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of The IHP/HEX Team. See list at end of paper. ...
The Astrophysical Journal, 2014
The Astrophysical Journal, 2008
We have surveyed He-Fe spectra for 41 Corotating Interaction Regions (CIRs) from 1998-2007 observ... more We have surveyed He-Fe spectra for 41 Corotating Interaction Regions (CIRs) from 1998-2007 observed on ACE. The spectra are similar for all species, and have the form of broken power laws with the spectral break occurring at a few MeV/nucleon. Except for overabundances of He and Ne, the abundances are close to those of the solar wind. We find the rare isotope He is enhanced in-40% of the events. In individual CIRs the Fe/O ratio correlates strongly with the solar wind Fe/O ratio measured 2-4 days prior to the CIR passage. Taken together with previously reported observations of pick-up He* in CIRs, these observations provide evidence that CIRs are accelerated out of a suprathermal ion pool of heated solar wind ions, pick-up ions, and remnant suprathermal ions from impidsive solar energetic particle (SEP) events.
The Astrophysical Journal, 2004
The Astrophysical Journal, 2006
We have surveyed the $0.1-10 MeV nucleon À1 abundances of heavy ions from 3 He through Fe in 64 l... more We have surveyed the $0.1-10 MeV nucleon À1 abundances of heavy ions from 3 He through Fe in 64 large solar energetic particle (LSEP) events observed on board the Advanced Composition Explorer from 1997 November through 2005 January. Our main results are (1) the 0.5-2.0 MeV nucleon À1 3 He/ 4 He ratio is enhanced between factors of $2-150 over the solar wind value in 29 ($46%) events. (2) The Fe/O ratio in most LSEP events decreases with increasing energy up to $60 MeV nucleon À1 . (3) The Fe/O ratio is independent of CME speed, flare longitude, event size, the 3 He/ 4 He ratio, the pre-event Fe/O ratio, and solar activity. (4) The LSEP abundances exhibit unsystematic behavior as a function of M/Q ratio when compared with average solar wind values. The survey-averaged abundances are enhanced with increasing M/Q ratio when compared with quiet coronal values and with average gradual SEP abundances obtained at 5-12 MeV nucleon À1 . (6) The event-to-event variations in LSEP events are remarkably similar to those seen in CME-driven IP shocks and in 3 He-rich SEP events. The above results cannot be explained by simply invoking the current paradigm for large gradual SEP events, i.e., that CME-driven shocks accelerate a seed population dominated by ambient coronal or solar wind ions. Instead, we suggest that the systematic M/Q-dependent enhancements in LSEP events are an inherent property of a highly variable suprathermal seed population, most of which is accelerated by mechanisms that produce heavy-ion abundances similar to those observed in impulsive SEP events. This heavy-ion-enriched material is subsequently accelerated at CME-driven shocks near the Sun by processes in which ions with higher M/Q ratios are accelerated less efficiently, thus causing the Fe/O ratios to decrease with increasing energy.
The Astrophysical Journal, 1978
ABSTRACT
The Astrophysical Journal, 2013
The Astrophysical Journal, 2001
The Astrophysical Journal, 1997
Because of the apparent difficulty in accelerating previously unaccelerated pickup ions locally a... more Because of the apparent difficulty in accelerating previously unaccelerated pickup ions locally at the solar wind termination shock, a model for anomalous cosmic-ray protons is considered in which the initial acceleration of pickup ions to ~10--20 MeV occurs in the inner heliosphere. These accelerated pickup ions are assumed to be accelerated either by propagating interplanetary shocks or by some other,
The Astrophysical Journal, 2004
We have surveyed the energy spectra of $0.1-100 MeV nucleon À1 C, O, and Fe nuclei associated wit... more We have surveyed the energy spectra of $0.1-100 MeV nucleon À1 C, O, and Fe nuclei associated with the passage of 72 interplanetary (IP) shocks observed on board the ACE spacecraft during the period 1997 October-2002 October. Our main results are as follows: (1) The spectral fit parameters are independent of the local shock properties. (2) About 7% of the events exhibit increasing Fe/O ratios with energy; the remaining events have Fe/O ratios that either remain constant or decrease with energy. ( The Fe/O ratio in the shock-associated particles is typically $30% lower than in the ambient population. (4) The fractionation pattern of the elemental abundances, the O spectra, and the energy-dependence of Fe/O at the IP shocks are remarkably similar to those of the ambient interplanetary suprathermal ion population. We suggest that the IP shocks studied here reaccelerate energetic particle seed spectra composed of ions from impulsive and gradual solar energetic particle events by systematic rigidity-dependent mechanisms in which higher rigidity ions are accelerated less efficiently than lower rigidity ions. Subject headingg s: acceleration of particles -interplanetary medium -shock waves 1156
The Astrophysical Journal, 1996
... of the heliocentric dependence of the relative abundance of low energy ( 1 MeV nucleon -1 ) c... more ... of the heliocentric dependence of the relative abundance of low energy ( 1 MeV nucleon -1 ) carbon and oxygen on the Ulysses ( 3 4 AU ... 1976; Barnes & Simpson 1976; Pesses, Van Allen, & Goertz 1978) and higher mass nuclei (eg, McGuire, von Rosenvinge, & McDonald 1978 ...
The Astrophysical Journal, 1985
... The shock wave was initiated by a solar flare, and its Alfvén Mach number at the position of ... more ... The shock wave was initiated by a solar flare, and its Alfvén Mach number at the position of Voyager 2 was MA ~ 3.4. The angle between the shock normal and the local upstream magnetic field was computed to be °B~, 87?5. II. ...
Space Science Reviews, 2009
Knowledge of the elemental composition of the interstellar gas is of fundamental importance for u... more Knowledge of the elemental composition of the interstellar gas is of fundamental importance for understanding galactic chemical evolution. In addition to spectroscopic determinations of certain element abundance ratios, measurements of the composition of interstellar pickup ions and Anomalous Cosmic Rays (ACRs) have provided the principal means to obtain this critical information. Recent advances in our understanding of particle acceleration processes in the heliosphere and measurements by the Voyagers of the energy spectra and composition of energetic particles in the heliosheath provide us with another means of determining the abundance of the neutral components of the local interstellar gas. Here we compare the composition at the termination shock of six elements obtained from measurements of (a) pickup ions at ∼5 AU, (b) ACRs in the heliosphere at ∼70 AU, and (c) energetic particles as well as (d) ACRs in the heliosheath at ∼100 AU. We find consistency among these four sets of derived neutral abundances. The average interstellar neutral densities at the termination shock for H, N, O, Ne and Ar are found to be 0.055 ± 0.021 cm −3 , (1.44 ± 0.45) × 10 −5 cm −3 , (6.46 ± 1.89) × 10 −5 cm −3 , (8.5 ± 3.3) × 10 −6 cm −3 , and (1.08 ± 0.49) × 10 −7 cm −3 , respectively, assuming the He density is 0.0148 ± 0.002 cm −3 .
Space Science Reviews, 2009
The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware a... more The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto's outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a "heavy comet" as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10s of keV to ~1 MeV in a 120° x 12° fan-shaped beam in six sectors for 1.5 kg and ~2.5 W.
Space Science Reviews, 1995
The spectra and anisotropies of ions =30 keV have been measured by the Low Energy Charged Particl... more The spectra and anisotropies of ions =30 keV have been measured by the Low Energy Charged Particle experiment on Voyagers 1 and 2 in the vicinity of interplanetary shocks between radial distances of 1–55 AU and heliographic latitudes 11° S-32° N. The spectra and anisotropies associated with a recent corotating (CIR) event at low latitude observed at Voyager 2 (36.6
Space Science Reviews, 1983
Space Science Reviews, 1977
The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft is designed to provid... more The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft is designed to provide comprehensive measurements of energetic particles in the Jovian, Saturnian, Uranian and interplanetary environments. These measurements will be used in establishing the morphology of the magnetospheres of Saturn and Uranus, including bow shock, magnetosheath, magnetotail, trapped radiation, and satellite-energetic particle interactions. The experiment consists of two subsystems, the Low Energy Magnetospheric Particle Analyzer (LEMPA) whose design is optimized for magnetospheric measurements, and the Low Energy Particle Telescope (LEPT) whose design is optimized for measurements in the distant magnetosphere and the interplanetary medium. The LEMPA covers the energy range from ~ 10 keV to > 11 MeV for electrons and from 15 keV to ³ 150 MeV for protons and heavier ions. The dynamic range is ~ 0.1 to ³ 10 11 (cm 2sec-sr) -1 overall, and extends to 10 13 (cm 2 -sec-sr) -1 in a current mode operation for some of the sensors. The LEPT covers the range ~ 0.05 £ E £ 40 MeV/nucleon with good energy and species resolution, including separation of isotopes over a smaller energy range. Multi-dE/dx measurements extend the energy and species coverage to 300-500 MeV/nucleon but with reduced energy and species resolution. The LEPT employs a set of solid state detectors ranging in thickness from 2 to ~ 2450 microns, and an arrangement of eight rectangular solid state detectors in an anticoincidence cup. Both subsystems are mounted on a stepping platform which rotates through eight angular sectors with rates ranging from 1 revolution per 48 minutes to 1 revolution per 48 seconds. A "dome" arrangement mounted on LEMPA allows acquisition of angular distribution data in the third dimension at low energies. The data system contains sixty-two 24-bit scalers accepting data from 88 separate channels with near 100% duty cycle, a redundant 256-channel pulse height analyzer (PHA), a priority system for selecting unique LEPT events for PHA analysis, a command and control system, and a fully redundant interface with the spacecraft. Other unique features of the LECP include logarithmic amplifiers, particle identifiers, fast (~ 15 ns FWHM) pulse circuitry for some subsystems, inflight electronic and source calibration and several possible data modes.
Space Science Reviews, 2007
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we sur... more 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 3 He is greatly enhanced over the corona or the solar wind values in 46% of the events.
Space Science Reviews, 2007
The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature ... more The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature magnetosphere since the brief flybys of Mariner 10. Mercury's magnetosphere is unique in many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands off the solar wind only -1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic particles and, hence, no radiation belts. The characteristic time scales for wave propagation and convective transport are short and kinetic and fluid modes may be coupled. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury's interior may act to modify the solar wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects may be an important source of information on the state of Mercury's interior. In addition, Mercury's magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived, -1-2 min, substorm-like energetic particle events observed by Mariner 10 during
Solar Physics, 1976
ABSTRACT Comprehensive measurements of the temporal variations of the Z 6 charge composition in t... more ABSTRACT Comprehensive measurements of the temporal variations of the Z 6 charge composition in the 4 July 1974 solar event made with experiments aboard IMP-7 and 8 show that large variations in the charge composition occur in three-hour-averaged intensities. Hourly averaged fluxes show variations as large as factors of 3 to 4 from one hour to the next and 3 hour averages show nearly a factor of 10 peak to minimum over the event. The precision of the measurements are limited by counting statistics of the Fe-group channel. Iron to oxygen variations are established by both rate channel and pulse height analysis techniques. Comparison of measurements from IMP-7 and 8, separated by about 70 R E shows that, while significant differences in composition and intensity exist for brief periods, the gross compositional variations are reproduced well at both spacecraft. These observations provide particularly stringent conditions for theories of the acceleration, release, and propagation of solar energetic particles.
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Papers by Stamatios Krimigis