Galactic supernova remnants

A progress report is given on our current interpretation of the X-ray emission from supernova remnants. Previous results from earlier experiments, the Einstein Observatory in particular, are reviewed and supplemented by the most recent data from the Exosat mission for a selection of remnants (Puppis-A, Cas-A, SN 1006, RCW103, W49B). Major improvements come from using the high energy spectra obtained with Exosat which indicate the presence of a very hot electron component in both young and old thermal remnants. Despite the fact that non-equilibrium ionization has been found in some cases, the spectra of most remnants investigated so far are not well represented by single non-equilibrium models, but require at least two components. An impression of the variety of plasma states which can be found in remnants is obtained from Exosat low energy filter spectroscopy of Puppis-A, which shows temperature variations on scales as small as 1.     

First detection of an X-ray burst and a one hour intensity dip in 4U1323-62

We report the results of a 1.4 10⁴s observation of the region of 4U 1323-62 with the EXOSAT ME. The source has a flux of 7–8 10^-11 erg/cm²s (2–10 keV) and a power-law spectrum with 1.1 < < 1.8. During our observation, the source showed a symmetric 60% dip in its X-ray flux of R~1 hr. The spectrum hardens during the dip. Inside the dip we observed an X-ray burst with a 2–10 keV peak flux of 7 10^-10 erg/cm²s. The burst spectrum is black-body, and shows evidence of cooling during the burst decay. The discovery of a burst from 4U 1323-62 settles the classification of the source; the observation of a dip suggests that we may be able to measure its orbital period in the near future.     

The Low Metallicity Tail of the Halo Metallicity Distribution Function

Ongoing spectroscopy and photometry of stars selected in the HK objective-prism/interference-filter survey of Beers and colleagues has resulted in the identification of many hundreds of additional stars in the halo (and possibly the thick disk) of the Galaxy with abundances [Fe/H] -2.0. A new calibration of the technique for estimation of metal abundance based on a CaII K index as a function of broadband B - V color is applied to obtain metallicities for stars observed with the SSO 2.3m and INT 2.5m telescopes. This new data is combined with other samples of extremely metal-deficient stars (Ryan and Norris, 1991a; Beers et al., 1992; Carney et al., 1994) to form a large database of objects of low metallicity. The combined sample is examined and compared with expectations derived from a Simple Model of Galactic chemical evolution. There appears to be a statistically-significant deficit of stars more metal-weak than [Fe/H] = -3.0. An abundance of [Fe/H] -4.0 can be taken as the low-metallicity limit for presently-observable stars in the Galaxy.     

The Time-of-Flight Energy,Angle, Mass Spectrograph (Teams) Experiment for Fast

The Time-of-flight Energy Angle Mass Spectrograph (TEAMS) is being flown on the FAST Small Explorer mission to measure the 3-dimensional distribution function of the major ion species present in the lower magnetosphere. The instrument is similar to time-of-flight plasma analyzer systems that have been designed and planned for flight as CODIF (COmposition and DIstribution Function analyzer) on the four European Space Agency Cluster-II spacecraft and, as ESIC (Equator-S Ion Composition instrument) on Equator-S. This instrument allows the 3-dimensional distribution functions of individual ion species to be determined within spin period (2.5 s). Two-dimensional distributions are measured in 80 ms. These capabilities are crucial for the study of selective energization processes in the auroral regions of the magnetosphere. The design, operational characteristics, and test and calibration results for this instrument are presented. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360° in polar angle. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated through calibration that the instrument can easily separate H⁺, He²⁺, He⁺, O⁺ and, for energies after post-acceleration of > 20 keV, even O₂ ⁺ molecules. On-board mass discrimination and the internal accumulation of several distinct data quantities combined with the spacecraft's flexible telemetry formatting allow for instrument data rates from 7.8 kb s^–1 to 315 kb s^–1 to be telemetered to ground through the FAST centralized Instrument Data Processor.     

Decay of Magnetic Field Irregularities Observed by Ulysses

We study the solar cycle, radial, and latitudinal dependence of the characteristics of magnetic field irregularities in the Heliosphere. The frequency of magnetic field discontinuities is determined, using high time resolution magnetic field observations by Ulysses, covering the time interval from 1992 to 2000. The quasi-linear scattering mean free path of particles is also calculated. These investigations aim at understanding/exploring transport properties of energetic charged particles in the Heliosphere. We find that the travel time of solar wind plasma from the Sun to the observer is the key parameter of the process, by controling the decay of the irregularities. This revised version was published online in August 2006 with corrections to the Cover Date.     

The FAST Satellite Fields Instrument

We describe the electric field sensors and electric and magnetic field signal processing on the FAST (Fast Auroral SnapshoT) satellite. The FAST satellite was designed to make high time resolution observations of particles and electromagnetic fields in the auroral zone to study small-scale plasma interactions in the auroral acceleration region. The DC and AC electric fields are measured with three-axis dipole antennas with 56 m, 8 m, and 5 m baselines. A three-axis flux-gate magnetometer measures the DC magnetic field and a three-axis search coil measures the AC magnetic field. A central signal processing system receives all signals from the electric and magnetic field sensors. Spectral coverage is from DC to 4 MHz. There are several types of processed data. Survey data are continuous over the auroral zone and have full-orbit coverage for fluxgate magnetometer data. Burst data include a few minutes of a selected region of the auroral zone at the highest time resolution. A subset of the burst data, high speed burst memory data, are waveform data at 2×10⁶ sample s^–1. Electric field and magnetic field data are primarily waveforms and power spectral density as a function of frequency and time. There are also various types of focused data processing, including cross-spectral analysis, fine-frequency plasma wave tracking, high-frequency polarity measurement, and wave-particle correlations.     

The 3-D Heliosphere from the Ulysses and ACE Solar Wind Ion Composition Experiments

The source region of solar wind plasma is observed to be directly reflected in the compositional pattern of both elemental and charge state compositions. Slow solar wind associated with streamers shows higher freeze-in temperatures and larger FIP enhancements than coronal hole associated wind. Also, the variability of virtually all compositional parameters is much higher for slow solar wind compared to coronal hole associated wind. We show that these compositional patterns persist even though stream-stream interactions complicate the identification based on in situ plasma parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rigidity Dependence and Time Response of Cosmic Rays to the Modulation Steps in the Rising Part of Solar Cycle 23. Cospin/ket Results

Previous work on the latitudinal gradient and on the amplitude of the recurrent cosmic ray decreases, has shown that their magnitude does not decrease monotonically with the particle rigidity, but it presents a broad maximun around 1–2 GV. We have extended this analysis to study the behaviour of cosmic-ray particles during the modulation steps in the rising part of the solar activity of the present Solar cycle. We found that the ‘depth’ of the modulation step decreases monotonically with increasing rigidity and that the least energetic particles are the last to reach their minimum intensity value. We also considered in this analysis electrons of equal rigidity to study the influence of the charge sign on the particle behaviour during the modulation steps. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ring Currents and Internal Plasma Sources

The discovery of terrestrial O⁺ and other heavy ions in magnetospheric hot plasmas, combined with the association of energetic ionospheric outflows with geomagnetic activity, led to the conclusion that increasing geomagnetic activity is responsible for filling the magnetosphere with ionospheric plasma. Recently it has been discovered that a major source of ionospheric heavy ion plasma outflow is responsive to the earliest impact of coronal mass ejecta upon the dayside ionosphere. Thus a large increase in ionospheric outflows begins promptly during the initial phase of geomagnetic storms, and is already present during the main phase development of such storms. We hypothesize that enhancement of the internal source of plasma actually supports the transition from substorm enhancements of aurora to storm-time ring current development in the inner magnetosphere. Other planets known to have ring current-like plasmas also have substantial internal sources of plasma, notably Jupiter and Saturn. One planet having a small magnetosphere, but very little internal source of plasma, is Mercury. Observations suggest that Mercury has substorms, but are ambiguous with regard to the possibility of magnetic storms of the planet. The Messenger mission to Mercury should provide an interesting test of our hypothesis. Mercury should support at most a modest ring current if its internal plasma source is as small as is currently believed. If substantiated, this hypothesis would support a general conclusion that the magnetospheric inflationary response is a characteristic of magnetospheres with substantial internal plasma sources. We quantitatively define this hypothesis and pose it as a problem in comparative magnetospheres.     

气固紊流剪切流中颗粒弥散的拉格朗日模拟

本文提出了一种对于气固两相紊流剪切流中圆形固体颗粒弥散的拉格朗日拟计算方法，其中考虑了颗粒间的磁撞对流体相和颗料相的影响，应用该方法对一气固紊流剪切流场进行了模拟计算，并对有、无颗粒间磁撞情况下的模拟计算结果与Lavieville用大涡模拟方法的研究结果进行了比较，并进行了讨论。