W. G. Fastie

Far-Ultraviolet Auroral Spectra

Further studies of the spectral data obtained in the February 1960 rocket experiment [ Ann. Geophys.17, 109 ( 1961)] have confirmed much of the preliminary analysis. New bands of the Lyman–Birge–Hopfield system in the 1700–2200 A region have been identified. More precise wavelength determinations have been made, and previously indicated bands of N2 have been more positively identified. The Lyman α line of hydrogen is just detectable. The intensity distribution among the various bands during weak auroral conditions is shown to differ markedly from more intense displays. Laboratory data obtained from a microwave discharge in very pure N2 show good correlation with some features of the rocket spectra.

Spatial imaging of hydrogen Lyman-alpha emission from Jupiter

A sounding rocket measurement of the H I L-alpha emission from Jupiter made on Dec. 1, 1978 shows limb darkening and an average disk brightness of 13 kR. This brightness is significantly higher than in previous measurements, and was confirmed by an IUE observation on Dec. 10, 1978. Comparison with a plane-parallel hydrogen layer model indicates that there is enhanced emission from the equatorial regions, reaching a peak near 80 deg longitude.

Spectroradiometric calibration techniques in the far ultraviolet - A stable emission source for the Lyman bands of molecular hydrogen

The problems associated with making accurate spectroradiometric measurements in the far uv region are sketched briefly. The equipment and methods that were developed for providing absolute sensitivity calibration of an Apollo 17 far uv spectrometer are described. The absolute reference standards were photoelectric diodes calibrated at the National Bureau of Standards. A complete vacuum optical facility, which included a premonochromator and stable uv light sources, was developed to calibrate the Apollo 17 instrument, and it has been used for a number of other tasks. Absolute radiometric calibrations between about 1200 A and 1700 A were performed with an absolute accuracy of +/-10%. The light source, which was designed to provide a very stable light output, is a low-pressure molecular hydrogen lamp in which the pressure is stabilized by thermal control of uranium hydride powder. Individual emission lines of the Lyman molecular band system of H(2) are used for calibration purposes. The lamp also copiously emits the 1215.7-A line (Lyalpha) of atomic hydrogen.

Mariner 6 and 7 ultraviolet spectrometers.

The ultraviolet spectrometers that observed the atmosphere of Mars in July and August of 1969 consist of a planetary coronagraph and an Ebert-Fastie monochromator. The spectral range 1100-4300 A was measured using two photomultiplier tubes, one with a cesium iodide photocathode, the other with a bialkali photocathode. These tubes were operated with fixed high voltage supplies and charge sensitive amplifiers. The instruments were calibrated by comparison with a tungsten lamp, a sodium salicylate screen, and a flowing nitric oxide cell. The instruments were able to satisfactorily reject off-axis light at a distance of 6600 km and measure the emission spectrum of the upper atmosphere 170 km above the surface.

Vacuum Ebert Grating Spectrometer

A new scanning spectrometer is described herein which is based almost exclusively on very recent technological advances and which, over the ultraviolet, visible, and near infrared region to 6 microns is capable of resolution and wavelength measuring accuracy comparable, on a wave-number basis, with the best that has been accomplished with spectrographs limited to the photographic region. The instrument is of the Ebert type and employs gratings as large as 5×7 inches, has a focal length of 72 inches, uses circularly curved slits 2 inches long, and can be triple passed. Specifications and performance are outlined.

Compact far ultraviolet emission source with rich spectral emission 1150–3100 Å

A new compact far uv emission source suitable for laboratory or space applications is described. The source is small, rugged, lightweight, spectrally rich, and bright in the 1150-3200-A region. It has met rigid spacecraft environmental tests and also is a very useful transfer standard for absolute sensitivity calibrations of spectrometric instruments.

New Spectrometer Slit Mechanism

A new type of slit mechanism is described which operates on the principle of the proving ring or loading ring. The load applied to distort a steel ring is the means by which the slit openings are varied and the opening determined. Very simple devices are described in which straight slit jaws are connected to opposite sides of a flexible ring and known weights are applied to the ring to obtain the desired slit opening. The mechanism has been used to provide very long dual curved slits for Ebert type monochromators, in which the proving ring itself acts as one jaw of the curved slits. The dual slits have been actuated by hydraulic pressure for vacuum operation.

A far-ultraviolet photometer for planetary surface analysis

The measurement of local variations in the far-ultraviolet albedo is explored as a means of detecting changes in the refractive index of rocks and dust on the surface of atmosphereless planets and satellites. Far-ultraviolet spectrophotometric measurements of the lunar surface which were obtained on the Apollo 17 orbital mission are presented to demonstrate that significant albedo variations occur in the spectral range 120 to 170 nm. These data also confirm the hypothesis that the albedo variations represent refractive index differences in the surface materials. A three-band photometer is described which, when put in orbit around a solar system object, is capable of providing refractive index maps with a sensitivity of 1 part in the second decimal place and with kilometer resolution. Comparative surface composition and surface history analyses based on such maps are discussed.

Rocket instrument for far-UV spectrophotometry of faint astronomical objects.

A sensitive sounding rocket instrument for moderate (~10-A) resolution far-UV (lambda1160-lambda1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employs a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.

Low-resolution ultraviolet spectroscopy of several hot stars observed from Apollo 17

Low-resolution ultraviolet spectra were obtained for six early-type stars in 1972 December, using an Ebert spectrometer mounted in the service module of the Apollo 17 spacecraft. The spectrometer scanned from 1180 A to 1680 A, with a speed that varied with wavelength according to a program chosen for lunar studies. Spectral resolution was 11 A. The ultraviolet absolute calibration of the instrument was determined by comparison with National Bureau of Standards calibrated photodiodes, and is believed known to plus-or-minus10 percent. Stars observed, with their spectral classes, were xi Oph (09.5),