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.     

An Exact Trajectory Solution from Doppler Shift Measurements

Three radar Doppler shift measurements are sufficient to determine the range and velocity, and the angle between them, of a target in uniform rectilinear motion. A solution using derivative approximations has recently appeared. An exact solution in terms of the original measurements is presented here.     

Transformer Induced Instability of the Series Resonant Converter

It is shown that the common series resonant power converter is subject to a low frequency oscillation that can lead to the loss of cyclic stability. This oscillation is caused by a low frequency resonant circuit formed by the normal L and C components in series with the magnetizing inductance of the output transformer. Three methods for eliminating this oscillation are presented and analyzed. One of these methods requires a change in the circuit topology during the resonance cycle. This requires a new set of steady state equations which are derived and presented in a normalized form. Experimental results are included which demonstrate the nature of the low frequency oscillation before cyclic stability is lost.     

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.