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.     

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.     

The long term variability of 4U 1258-61 (GX304-1)

We present optical spectroscopy and photometry of 4U 1258-61 obtained over the course of six years. Evidence for the evolution of a circumstellar envelope throughout the course of the observations is presented.     

Voyager 2 Solar Wind Observations in the Outer Heliosphere

We discuss the solar wind parameters measured in the distant heliosphere from the Voyager 2 spacecraft. Periodic variations in the speed of the wind observed at roughly the solar rotation period may correspond to interaction regions between slower and faster streams of wind. Since the interplanetary magnetic field is enhanced in such regions, they are important for the study of modulation of cosmic rays. Unfortunately, direct observation of the enhanced magnetic field from Voyager 2 has been made difficult by spacecraft-associated noise since 1989.     

Experiments in Adaptive Estimation of Unknown Binary Waveforms

A special-purpose adaptive machine is described which carries out estimation in real time of an unknown binary waveform which is perturbed with additive Gaussian noise. Unknown waveforms of over 103 samples in duration can be recovered. The unknown waveforms are of unknown epoch and can reappear at either random or periodic time intervals. The observed signal is received at moderate or low signal-to-noise ratios so that a single observation of the received data (even if one knew the precise signal arrival time) is not sufficient to provide a good estimate of the signal waveshape. Experimental results are described which show transient behavior waveform estimate. The transient behavior is expressed as the number of errors in the current estimate of the signal plotted vs. time. In a noisy environment, each ``learning' transient is a random time function. These learning transients are shown for several different signal-to-noise ratios and indicate the threshold noise levels for various types of initial states of the machine memory.     

Radio observations of Venus and the interpretations

The radio observations of Venus are reviewed and compared with theoretical microwave spectra computed for a variety of models of the Venusian environment. The models considered are (a) a CO₂-N₂ atmosphere, (b) an atmosphere of dust (the aeolosphere model), and (c) a cloud model with various loss mechanisms in the cloud. The effect of polarization on the surface emissivity has been included in all the computations. It is shown how the radio observations place limits upon the acceptable models, for example, the density and size of dust particles required in the aeolosphere model. It is shown how some models place severe restrictions on radar observations at short centimeter wavelengths, thereby emphasizing the importance of such experiments. These same models show that the Mariner II observations can not be interpreted in terms of surface phenomena and provide a new interpretation for the microwave phase effect.This work was supported in part by the U.S. Army, Navy and Air Force under Contract DA36-039-AMC-03200(E); and in part by the National Aeronautics and Space Administration (Grants NsG-250-62 and NsG-419).     

Modified Generalized Sign Test Processor for 2-D Radar

The modified generalized sign test processor is a nonparametric, adaptive detector for 2-D search radars. The detector ranks a sample under test with its neighboring samples and integrates (on a pulse-to-pulse basis) the ranks with a two-pole filter. A target is declared when the integrated output exceeds two thresholds. The first threshold is fixed and yields a 10-6 probability of false alarm when the neighboring samples are independent and identically distributed. The second threshold is adaptive and maintains a low false-alarm rate when the integrated neighboring samples are correlated and when there are nonhomogeneities, such as extraneous targets, in the neighboring cells. Using Monte Carlo techniques, probability of false-alarm results, probability of detection curves, and angular accuracy curves have been generated for this detector. The detector was built and PPI photographs are used to indicate the detector's performance when the radar is operated over land clutter.