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Silk, J. K.

Publications and source records attributed to Silk, J. K..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The design and evaluation of grazing incidence relay optics

X-ray astronomy, both solar and celestial, has many needs for high spatial resolution observations which have to be performed with electronic detectors. If the resolution is not to be detector limited, plate scales in excess of 25 microns arc/sec, corresponding to focal lengths greater than 5 m, are required. In situations where the physical size is restricted, the problem can be solved by the use of grazing incidence relay optics. A system was developed which employs externally polished hyperboloid-hyperboloid surfaces to be used in conjunction with a Wolter-Schwarzschild primary. The secondary is located in front of the primary focus and provides a magnification of 4, while the system has a plate scale of 28 microns arc/sec and a length of 1.9 m. The design, tolerance specification, fabrication and performance at visible and X-ray wavelengths of this optical system are described.

Davis, John M.↗
NASA NTRS1980

A two-temperature model for the flare of 5 September, 1973

A study of the energetics and mass transfer during the X-ray flare on Sept. 5, 1973, using the observations in the objective grating mode of the spectrographic telescope on Skylab is presented. The data are approximately monochromatic images of a small X-ray source which show a continued rise in the emission for several minutes followed by a decline. The observations are analyzed using a two-temperature model to determine the changes in the distribution of emission measure and of the amount of material as a function of temperature. The development of the flare can be divided into three periods comprising evaporation which drives mass into the entire emitting region, cessation of evaporation, and decline in the emission measure.

Little-Marenin, I. R.↗
NASA NTRS1979

Quest for ultrahigh resolution in X-ray optics

A program of solar X-ray astronomy using grazing incidence optics has culminated in X-ray images of the corona having one arc second spatial resolution. These images have demonstrated that, in general, X-ray optics can be fabricated to their specifications and can provide the level of resolution for which they are designed. Several aspects of these programs relating to the performance of X-ray optics in regard to resolution, including the point response function, the variation of resolution with off-axis position and the recognition that nearly all solar X-ray images have been film limited, are discussed. By extending the experience gained on this and other programs it is clearly possible to design and fabricate X-ray optics with sub arc sec resolution. The performance required to meet the scientific objectives for the remainder of the century are discussed in relation to AXIO, an Advanced X-Ray Imaging Observatory for solar observations which is proposed for flight on the Space Shuttle. Several configurations of AXIO are described, each of which would be a major step in the quest for ultrahigh-resolution observations.

Davis, J. M.↗
NASA NTRS1978

An atlas of soft X-ray images of the solar corona from Skylab

An atlas is presented which contains daily full-sun photographs of the soft X-ray solar corona taken in two filters with an X-ray telescope on the Apollo telescope mount of Skylab for the period from May 29 to November 27, 1973. The passband of the first filter covers the wavelength regions from 2 to 32 A and 44 to 54 A; the second filter covers the region from 2 to 17 A. Characteristics of the instrument, the wavelength response, and sensitivity are described along with the total data base, of which the atlas represents only 1%. Comparisons are made with observations of the white-light corona, photospheric magnetic field, H-alpha radiation from the chromosphere, and 284-A Fe XV emission from the corona. A complete bibliography of scientific papers that have used the data base and a bibliography of catalogs and atlases containing related data for the same observational period are provided.

Zombeck, M. V.↗
NASA NTRS1977

The S-054 X-ray telescope experiment on Skylab

A description of the S-054 X-ray telescope on Skylab is presented with a discussion of the experimental objectives, observing program, data reduction and analysis. Some results from the Skylab mission are given. The telescope photographically records high-resolution images of the solar corona in several broadband regions of the soft X-ray spectrum. It includes an objective grating used to study the line spectrum. The spatial resolution, sensitivity, dynamic range and time resolution of the instrument were chosen to survey a wide variety of solar phenomena. It embodies improvements in design, fabrication, and calibration techniques which were developed over a ten-year period. The observing program was devised to optimize the use of the instrument and to provide studies on a wide range of time scales. The data analysis program includes morphological studies and quantitative analysis using digitized images. A small sample of the data obtained in the mission is presented to demonstrate the type of information that is available and the kinds of results that can be obtained from it.

Vaiana, G. S.↗
NASA NTRS1977

High resolution X-ray optics for astronomical and laboratory sources

In recent years X-ray telescopes have been used successfully for high resolution observations of astronomical objects, in particular the solar corona. At the present time X-ray microscopes are being developed for diagnostics of laser and electron beam induced fusion plasmas. This paper describes both types of imaging systems using as examples the AS&E X-ray telescope on Skylab and a 10X microscope being built for Los Alamos Scientific Laboratories. The designs, manufacturing tolerances, fabrication, testing, and performance are discussed. Steps for further development in both imaging areas are identified.

Silk, J. K.↗
NASA NTRS1976

The temperature and density structures of an X-ray flare during the decay phase

The X-ray flare of 9 August 1973 was characterized by a spatially small kernel structure which persisted throughout its duration. The decay phase of this flare was observed in the objective grating mode of the X-ray telescope aboard the Skylab. Data analysis was carried out by scanning the images with a microdensitometer, converting the density arrays to energy using laboratory film calibration data and taking cross sections of the energy images. The 9 August flare shows two distinct periods in its decay phase, involving both cooling and material loss. The objective grating observations reveal that the two phenomena are separated in time. During the earlier phase of the flare decay, the distribution of emission measure as a function of temperature is changing, the high temperature component of the distribution being depleted relative to the cooler body of plasma. As the decay continues, the emission measure distribution stabilizes and the flux diminishes as the amount of material at X-ray emitting temperatures decreases.

Silk, J. K.↗
NASA NTRS1975

The location of the site of energy release in a solar X-ray subflare

A rapid sequence of high-resolution X-ray photographs was obtained by the S-054 X-ray Telescope Experiment on Skylab on 1973 September 1. During the course of this observation, photographs were obtained of a flarelike brightening in a simple, bipolar active region. Analysis reveals the following facts. The event had the form of a small, elongated bright feature whose narrowest dimension was less than seconds of arc. The brightness peak of the flarelike brightening was located within seconds of arc of the center of brightness of a preexisting loop structure that crossed the magnetic neutral line. This loop was observed to brighten gradually beginning approximately 10 minutes prior to the flarelike event. During the rise of the event, the 2-17 A X-ray brightness of the center of the subflare core rose by over a factor of 10 in a time period of 196 seconds or less.

Petrasso, R. D.↗
NASA NTRS1974

The X-ray spectrographic telescope

The S-054 X-ray telescope, which operated successfully throughout the eight-month Skylab mission, is a grazing incidence instrument with a spatial resolution of the order of 2 arc sec on axis. The total wavelength range observed by the instrument is 2 to 60 A. Crude spectral resolution within this range is achieved by means of a series of six X-ray filter materials. A spectrographic mode of operation, employing an objective grating, is used to obtain spectra of flare events and selected coronal features.

Vaiana, G. S.↗
NASA NTRS1973

X-ray observations of characteristic structures and time variations from the solar corona - Preliminary results from Skylab.

Examples taken from the S-054 X-ray telescope observations made during the first Skylab mission show the hot coronal plasma tracing the configuration of the magnetic fields. The high spectral resolution and sensitivity of the instrument has enabled the following two facts to be more firmly established: (1) that the 'quiet homogeneous corona' is in fact highly structured and that the structures observed appear to be the results of dispersed active region magnetic fields; and (2) that numerous bright points are distributed randomly on the disk. Their presence at high latitudes may play a role in solar cycle models. In addition, the capability of Skylab for studying time evolution has enabled the restructuring of coronal features to be seen at times of high activity, indicating a restructuring of the coronal magnetic fields.

Vaiana, G. S.↗
NASA NTRS1968

Laser-Doppler gas-velocity instrument

Three-D instrument using a laser light source measures both turbulence and mean velocity of subsonic and supersonic gas flows. This instrument is based on the measurement of the Doppler frequency shift of light waves scattered by moving particles in the gas stream.

Booth, S.↗