An Update on Ultra-Heavy Elements in Solar Energetic Particles above 10 MeV/Nucleon

Measurements below several MeV/nucleon from Wind/LEMT and ACE/ULEIS show that elements heavier than Zn (Z=30) can be enhanced by factors of ∼100 to 1000, depending on species, in ³He-rich solar energetic particle (SEP) events. Using the Solar Isotope Spectrometer (SIS) on ACE we find that even large SEP (LSEP) shock-accelerated events at energies from ∼10 to >100 MeV/nucleon are often very iron rich and might contain admixtures of flare seed material. Studies of ultra-heavy (UH) SEPs (with Z>30) above 10 MeV/nucleon can be used to test models of acceleration and abundance enhancements in both LSEP and ³He-rich events. We find that the long-term average composition for elements from Z=30 to 40 is similar to standard solar system values, but there is considerable event-to-event variability. Although most of the UH fluence arrives during LSEP events, UH abundances are relatively more enhanced in ³He-rich events, with the (34<Z<40)/O ratio on average more than 50 times higher in ³He-rich events than in LSEP events. At energies >10 MeV/nucleon, the most extreme event in terms of UH composition detected so far took place on 23 July 2004 and had a (34<Z<40)/O enhancement of ∼250–300 times the standard solar value.     

Long-Term Fluences of Solar Energetic Particles from H to Fe

Data from ACE and GOES have been used to measure Solar Energetic Particle (SEP) fluence spectra for H, He, O, and Fe, over the period from October 1997 to December 2005. The measurements were made by four instruments on ACE and the EPS sensor on three GOES satellites and extend in energy from ∼0.1 MeV/nuc to ∼100 MeV/nuc. Fluence spectra for each species were fit by conventional forms and used to investigate how the intensities, composition, and spectral shapes vary from year to year.     

Magnetic connectivity and solar energetic proton event intensity profiles at deka-MeV energy

We present an analysis of the time-intensity profiles of 25 solar energetic proton events at 18.2 MeV, modelled by fitting an analytical function form (a modified Weibull function) to the observed intensities. Additionally relying on previous work that characterized the magnetic connectivity between the event-related solar flare and the observer in these events with three angular parameters, we investigate the fit function parameters, the connectivity parameters, and the iron-to-carbon ratio of the events for dependencies and correlations. We find that the fit parameter controlling the basic shape of the profile (parameter a) is not clearly dependent on the connectivity parameters or the Fe/C ratio, suggesting that the profile shapes of neither well and weakly connected nor generally “impulsive” and “gradual” events differ systematically during the early stages of the event at 1 AU. In contrast, the time scaling of the fit function (parameter b) is at least moderately correlated with both the magnetic connectivity parameters and the Fe/C ratio, in that well-connected and iron-rich events are typically shorter in relative duration than weakly connected and nominal-abundance events; intensity rise times display a similar correlation with the connectivity parameters. We interpret the former result as following from the combined effect of various transport processes acting on the particles in interplanetary space, while the latter is essentially consistent with established knowledge regarding the observed dependence of the time-intensity profile shapes of solar energetic particle events on their magnetic connectivity and heavy ion abundances. The desirability of modelling the particle transport effects in detail and extending the analysis to cover higher energies is indicated.     

The X-Ray Spectrometer on the MESSENGER Spacecraft

NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12° field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes XRS’s science objectives, technical design, calibration, and mission observation strategy.     

XMM-Newton observations across the Cygnus Loop from northeastern rim to southwestern rim

We have observed the Cygnus Loop from the northeast (NE) to the southwest (SW) with XMM-Newton. We extracted spectra from 3′-spaced annular regions across the Loop and fitted them either with a one-kT_e-component non-equilibrium ionization (NEI) model or with two-kT_e-component NEI model. We found that the two-kT_e-component model yields significantly better fits in almost all the spectra than the one-kT_e-component model. Judging from the abundances, the high-kT_e-component in the two-temperature model must be fossil ejecta while the low-kT_e-component comes from the swept-up interstellar medium (ISM). The distributions of Ne, Mg, Si, and S for fossil ejecta appear to retain the onion-skin structure at the time of a supernova explosion, suggesting that significant overturning of the ejecta has not occurred yet. Comparing the relative abundances of fossil ejecta estimated for the entire Cygnus Loop with those from theoretical calculations for Type-II SN, the mass of the progenitor star is likely to be ∼13 M_⊙. The trends of the radial profiles of kT_e and emission integral for the swept-up ISM are adequately described by the Sedov model, suggesting that the swept-up ISM is concentrated in a shell-like structure. Comparing our data with the Sedov model, we found the ambient medium density to be ∼0.7 cm⁻³. Then, we estimated the total mass of the swept-up ISM and the age of the remnant to be ∼130 M_⊙ and 13,000 years, respectively. Note that if the explosion occurred within a stellar wind cavity, then the density in the cavity, the total swept-up mass in the cavity, and the age of the remnant are estimated to be ∼0.14 cm⁻³, ∼25 M_⊙, and ∼10,000 years, respectively.     

The isotopic composition of anomalous cosmic rays from sampex

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.     

Measurements of the 12C/13C Ratio in Planetary Nebulae and Implications for Stellar Evolution

We present the results of a study aimed at determining the 12C/13C ratio in two samples of planetary nebulae (PNe) by means of mm-wave observations of 12CO and 13CO. The first group includes six PNe which have been observed in the 3He+ hyperfine transition; the other group consists of 23 nebulae with rich molecular envelopes. We have determined the isotopic ratio in 14 objects and the results indicate a range of values between 9 and 23. In particular, three PNe have ratios well below the value predicted by standard evolutionary models ( 20), indicating that some extra-mixing process has occurred in these stars. We briefly discuss the implications of our results for standard and nonstandard stellar nucleosynthesis.     

Relative ion Fe,C and O abundances in quiet time particle fluxes in the 23 SC

Using ACE and SOHO data the origin of quiet-time low-energy particle fluxes at 1 AU is studied in the 23rd solar cycle. One of the selection criteria of quiet-time periods is to demand that H/He < 10 provided that periods with noticeable contribution of remnants of gradual events have been excluded from consideration. Our results suggest different origin of 0.03–3 MeV/nucleon particles – different seed populations accelerated and different acceleration processes. During the ascending, maximum and descending phases of solar activity quiet-time ions consist of coronal particles accelerated to suprathermal energies in about a half of the quiet periods, the rest of quiet-time fluxes originates from particle acceleration in processes similar to those in small impulsive solar flares rich in Fe. At solar minimum the bulk solar wind particles serve as seed population.     

Standard Solar Composition

We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution. This revised version was published online in June 2006 with corrections to the Cover Date.