Interplanetary shock waves: Ulysses observations in and out of the ecliptic plane

Between its launch in October 1990 and the end of 1993, approximately 160 fast collisionless shock waves were observed in the solar wind by the Ulysses space probe. During the in-ecliptic part of the mission, to February 1992, the observed shock waves were first caused mainly by solar transient events following the solar maximum and the reorganisation of the large scale coronal fields. With the decay in solar activity, relatively stable Corotating Interaction Regions (CIRs) were observed betwen 3 and 5.4 AU, each associated with at least one forwardreverse shock pair. During the out-of-ecliptic phase of the orbit, from February 1992 onwards, CIRs and shock pairs associated with them continued to dominate the observations. From July 1992, Ulysses encountered the fast solar wind flow from the newly developed southern polar coronal hole, and from May 1993 remained in the unipolar magnetic region associated with this coronal hole. At latitudes beyond 30°, CIRs were associated almost exclusively with reverse shocks only. A comprehensive list of shock waves identified in the magnetic field and solar wind plasma data from Ulysses is given in Table 1. The principal characteristics were determined mainly from the magnetic field data. General considerations concerning the determination of shock characteristics are outlined in the Introduction.     

螺桨滑流对全机绕流干扰的数值计算

 数值计算采用面元法。在桨叶及全机面元的控制点上强加 Neumann条件以实现滑流与全机流场的相互耦合。计算中考虑了三维螺桨滑流的收缩及其对流场的影响。最后对运七全机气动力作了计算。结果表明 ,滑流对全机放襟翼状态升力特性有明显影响 ,使全机力矩特性产生较大变化。计算结果与实验值吻合良好。该方法对单发或多发螺桨飞机均适用     

X-Ray spectroscopic investigation of the coronal structure of capella

The binary system Capella (G6 III + F9 III) has been observed on 1979 March 15 and on 1980 March 15–17 with the Objective Grating Spectrometer (OGS) onboard theEinstein Observatory. The spectrum measured with the 1000 l/mm grating covers the range 5–30 Å with a resolution < 1 Å. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component 5 million degrees and the other one 10 million degrees. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the Sun. It is shown that the conditions required by this model exist on Capella. Mean values of loop parameters are derived for both temperature components.     

The Rosat mission

The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 10⁵) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 2⁰ × 2⁰.     

Self-Cohering an Airborne e Radio Camera

By distributing antenna elements or small subarrays throughout the skin of an aircraft, a large portion of the airframe can act as an electromagnetic transducer. The basic problem associated with such a design is that uncertainties in element locations due to the nonrigidness of the airframe induce phase errors. Self-cohering techniques are required to compensate for those errors. Four such techniques are presented here.     

Spectra and time variability of GX 5-1

From a short observation of GX 5-1 with EXOSAT we have derived information on spectral and temporal behaviour in the energy range 1–20 keV. The source was found to be variable on time scales from 10 s to 1 h. Describing the spectrum one is forced to assume at least two spectral components. The best fit is reached using a spectrum composed of two blackbody functions with typical temperatures 1 keV and 2 keV, corresponding to apparent blackbody radii of 43 km and 11 km, respectively (for a distance of 10 kpc). With respect to the hot component there is evidence for variability in temperature as well as in apparent blackbody radius. No periodic variability has been found over the period range 0.25 s to 2000 s. There is no evidence for an iron emission line.     

An investigation into the nature of the 4.4 hr periodic source 4U1755-33

We present the results of a continuous 18 hour observation of 4U1755-33 made with the European Space Agency's EXOSAT Observatory. Four 50 min dips in X-ray intensity were observed equally spaced with a period of 4.4 hrs, confirming the periodicity first suggested in White et al. (1984). The dips are spectrally independent. We examine the properties of 4U1755-33 and conclude that the source is most probably point-like and that the metallicity of the absorbing material is at least 600 times less than cosmic values.     

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.