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At least 397 records · Page 22

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NASA NTRS1981

Spatial imaging of UV emission from Jupiter and Saturn

Spatial imaging with the IUE is accomplished both by moving one of the apertures in a series of exposures and within the large aperture in a single exposure. The image of the field of view subtended by the large aperture is focussed directly onto the detector camera face at each wavelength; since the spatial resolution of the instrument is 5 to 6 arc sec and the aperture extends 23.0 by 10.3 arc sec, imaging both parallel and perpendicular to dispersion is possible in a single exposure. The correction for the sensitivity variation along the slit at 1216 A is obtained from exposures of diffuse geocoronal H Ly alpha emission. The relative size of the aperture superimposed on the apparent discs of Jupiter and Saturn in typical observation is illustrated. By moving the planet image 10 to 20 arc sec along the major axis of the aperture (which is constrained to point roughly north-south) maps of the discs of these planets are obtained with 6 arc sec spatial resolution.

Clarke, J. T.↗

NASA NTRS1980

The remote-controlled spectrograph, area scanner, and spectropolarimeter for the Lick 3-m telescope

A Cassegrain spectrograph used in conjunction with an image-tube, image-dissector scanner (ITS) is discussed with reference to its design features and operation. The spectrograph has a remote control feature, and its parameters, such as slit width, decker position, filter selection, focus, and grating selection, can be easily changed by computer command or a hard-wired control box. The discussion also includes the area scanner modification which allows raster scanning and limited picture taking. Finally, the design of a two-channel polarization analyzer is presented which allows simultaneous sky and sky-plus-star observations and faint-object polarimetry.

Miller, J. S.↗

NASA NTRS1980

Multiple object spectroscopy - The Medusa spectrograph

An instrument has been built to obtain simultaneous spectra of many objects in the field of view of the Steward 90 inch (2.29 m) telescope. Short lengths of fused silica fiber 300 microns in diameter are used to bring the light from galaxy images at the Cassegrain focus into a line along the spectrograph slit. From a single exposure of the cluster Abell 1904, which has a redshift of 20,000 km/s, the redshifts of 26 individual galaxies were determined, each with a precision of 100 km/s. The present device, while already giving a sixfold reduction in the mean telescope time per galaxy, has significant light losses because it is not ideally matched to the telescope. An instrument being designed for the prime focus will transmit light from each object as efficiently as a conventional spectrograph.

Hill, J. M.↗

NASA NTRS1981

Performance and design of the ultraviolet spectrometer and polarimeter on the solar maximum mission

The instrument observes spectral line intensity, Doppler motions, and polarization parameters. First Dopplergrams of the sun showing mass motion of prominences have been obtained. The instrument consists of a telescope, a spectrometer, a polarimeter, and five detectors. Spectral range extends from 1150 to 3600 Angstroms. The telescope is an alphanatic Gregorian capable of scanning a 256 x 256 arcsecond raster. The spectrometer is an Ebert-Fastie mount with exchangeable slits for intensity measurements and spectroscopy. Detectors are photomultipliers operating in the pulse-counting mode.

Sterk, A. A.↗

NASA NTRS1981

Stratospheric trace constituent profile retrievals using laser heterodyne radiometer IR limb sensing spectra

A retrieval technique for high resolution IR solar occultation limb sensing data is described for profiling stratospheric trace constituents. Remote measurement of ClO during sunset in the 24-45-km region with a 2-km height resolution is chosen as an example. Two types of instruments are considered: a laser heterodyne radiometer with line resolving spectral resolution and an interferometer spectrometer with a fixed slit width of 0.02/cm. It is pointed out that a multichannel approach is necessary with the heterodyne instrument for improved retrieval accuracy. The error analysis indicates the relative sizes of instrument noise and other sources of error in the retrieval of altitude profiles with high (2-km) vertical resolution.

Majumdar, A. K.↗

NASA NTRS1981

Spectral transmission measurements in the nu sub 6 fundamental of /C-12/H3D at 8.65 microns

Spectral transmission measurements were performed at 300 K in the 8.65-micron fundamental band of monodeuterated methane, a trace constituent in the atmosphere of Jupiter. A theoretical curve is obtained from line-by-line computation of the spectral transmission utilizing a triangular slit function with full width at half-maximum. The agreement between theoretical and experimental spectral transmission curves suggests that deuteration does not affect the collision-broadened half-widths significantly in the two extreme cases of broadening being considered.

Varanasi, P.↗

NASA NTRS1980

Ultraviolet albedo of Comet West /1976 VI/

The nature of the dust scattered radiation shown in the ultraviolet spectrum of Comet West is analyzed. The continuum of solar radiation scattered by cometary dust is detected to wavelengths as short as 2100 A and is found to follow closely the solar spectrum. The flux from the entire visible coma is included in the spectrometer slit. A comparison of the ultraviolet with the visible solar flux gives the ratio of the albedo at 2700 A to that of 5500 A as about 0.3. Even with all the uncertainties included (the absolute calibration uncertainty is plus or minus 15%), the evidence for strong reddening between the visible and the ultraviolet is clear. A further decrease in albedo is found near 2200 A. The value of the visible albedo of 0.2 is used to derive a value of 0.6 for the cometary albedo at 2700 A. This value is similar to that found for the moon and lunar dust in this spectral region.

Feldman, P. D.↗

NASA NTRS1981

Determining the electron energy distribution near the plasma potential in the earth's ionosphere

A determination of the plasma potential using an electrostatic analyzer is described in which the potential difference between the instrument slit system and surrounding plasma is minimized. Data obtained from rocket-borne instrumentation demonstrate the viability of this technique for electron fluxes between thermal energies (about 0.5 V) and suprathermal energies (many volts).

Sharp, W. E.↗

NASA NTRS1981

Solar Maximum Mission Experiment - Ultraviolet Spectroscopy and Polarimetry on the Solar Maximum Mission

The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacecraft is described. It is pointed out that the instrument, which operates in the wavelength range 1150-3600 A, has a spatial resolution of 2-3 arcsec and a spectral resolution of 0.02 A FWHM in second order. A Gregorian telescope, with a focal length of 1.8 m, feeds a 1 m Ebert-Fastie spectrometer. A polarimeter comprising rotating Mg F2 waveplates can be inserted behind the spectrometer entrance slit; it permits all four Stokes parameters to be determined. Among the observing modes are rasters, spectral scans, velocity measurements, and polarimetry. Examples of initial observations made since launch are presented.

Tandberg-Hanssen, E.↗

NASA NTRS1981

Spectrometry of Jupiter at selected locations on the disk during the 1979 apparition

Jupiter's reflectivity was measured as a function of wavelength between 3000 and 10,500 Angstrom for two nights during the 1979 apparition. The spectra obtained were used to calibrate the wavelength response of Voyager images and to establish differences from previous apparitions. The observations were taken in the prominent belts and zones and both polar caps along the central meridian using a slit of dimensions 2.33 x 2.5 sq arcsec. The equivalent widths of the 6190 and 7270 Angstrom CH4 bands were measured; compared to the 1976 apparition, there was significantly less CH4 absorption in the north tropical zone. Such equivalent-width decreases are said to result from either a reduction in particle albedo or a decrease in the scattering mean free path owing to a greater concentration of aerosol particles in the NTrZ.

Cochran, A. L.↗

NASA NTRS1981

The aluminum I autoionization doublet in the quiet solar spectrum

Observations are presented of the Al I autoionization doublet 1932 A and 1936 A in the quiet solar spectrum, obtained from the NRL slit spectrograph aboard Skylab and from the University of Hawaii Echelle Rocket Spectrograph. The observed profiles are compared with theoretical spectra computed for the Harvard Smithsonian Reference Atmosphere and the Vernazza, Avrett and Loeser (1976) solar models. It is found that nonlocal thermodynamic equilibrium effects are important in the line-formation problem and the synthetic spectra are in good agreeement with the data.

Heasley, J. N.↗

NASA NTRS1951

X-Ray Diffraction Study of the Internal Structure of Supercooled Water

A Bragg X-ray spectrometer equipped with a volume-sensitive Geiger counter and Soller slits and employing filtered molybdenum Ka radiation was used to obtain a set of diffracted intensity curves as a Punction of angle for supercooled water. Diffracted intensity curves in the temperature region of 21 to -16 C were obtained. The minimum between the two main diffraction peaks deepened continuously with lowering temperature, indicating a gradual change in the internal structure of the water. No discontinuity in this trend was noted at the melting point. The internal structure of supercooled water was concluded to become progressively more ice-like as the temperature is lowered.

Dorsch, Robert G.↗

NASA NTRS1981

A possible technique for cometary studies with high angular and spectral resolution

The echelle spectrographs, designed for and used at the Cassegrain stations of the KPNO and CTIO 4-meter telescopes, are capable of cometary spectroscopy with seeing-limited angular resolution along the slit and with spectral resolving power (lambda/delta lambda) ranging from 10 to the 4th power to 10 to the 5th power. Various gratings, cameras and detectors can be used in combination for specific studies in the 3000A to 10,000A range.

Gull, T. R.↗

NASA NTRS1981

Narrow passband imagery of comets

During an emission-line survey of the Milky Way, Comet West was accidently imaged through four different narrow passbands with a wide-field, image-intensified camera. Three passbands recorded very similar head plus tail structure. The fourth passband shows an additional large, diffuse component around the head. It was serendipitous that such was recorded as the filters, being selected for studies of emission nebulae, are not particularly suited for studies of comets. However the imagery, plus subsequent studies, suggests that much can be learned about the structure of comets using narrow passband imagery simultaneously with long slit spectroscopy.

Gull, T. R.↗

NASA NTRS1981

Photographic observations of comets at Lowell Observatory

Observations of Halley's comet at Lowell Observatory cover a period from November 10, 1909 to May 17, 1911: 334 direct photographs were taken, 118 objective prism spectra, and 32 slit spectrograms of the nucleus, many of them including 5 arc minutes of the surrounding coma. Just one morning's observations are illustrated as an example of utilizing every possible resource available at the Observatory at the time. Observational improvements developed since then are described and some suggestions for the coming return of Halley's comet are made.

Giclas, H. L.↗

NASA NTRS1980

Advanced Gas Turbine (AGT) powertrain system initial development report

The powertrain consists of a single shaft regenerated gas turbine engine utilizing ceramic hot section components, coupled to a slit differential gearbox with an available variable stator torque converter and an available Ford intergral overdrive four-speed automatic transmission. Predicted fuel economy using gasoline fuel over the combined federal driving cycle (CFDC) is 15.3 km/1, which represents a 59% improvement over the spark-ignition-powered baseline vehicle. Using DF2 fuel, CFDC mileage estimates are 17.43 km/1. Zero to 96.6 km/hr acceleration time is 11.9 seconds with a four-second accleration distance of 21.0 m. The ceramic radial turbine rotor is discussed along with the control system for the powertrain.

Source record↗

NASA NTRS1982

Determination of the efficiency of a proportional counter for detecting X-rays

A parallel beam of X-rays (approximately monoenergetic) passing through a rectangular slit and scattering from two flat mirrors comprise the X-ray test. The two mirrors are arranged in a periscope geometry so that the final reflected beam is parallel to the incident beam but displaced laterally by given amount. One of the detectors used to intercept the reflected X-rays is a one dimensional gas-filled proportional counter which is sensitive to the position (in 1 dimension) at which the X-rays are incident within its detecting "window". The total length of the anode wire of the proportional counter is 120 mm and this length can be divided electronically into a maximum of 1,024 parts. Hence, the output of an experimental run would be the number of incident X-rays that registered on each of the 1,024 channels. Each channel would represent an X-ray at a different spatial location and, hence, at a different scattering angle. In order to look at a wider range of scattering angles, the detector is placed on an optical table which can be rotated.

Williams, A. C.↗

NASA NTRS1981

Very wide field camera

The study of galactic and faint extragalactic extended sources and peculiar ultraviolet objects by a very wide field of view camera, operated in the ultraviolet photometric and spectrometric modes is discussed. The photometric mode is direct photography through filters for observation of the following sources: (1) large scale distribution of ultraviolet radiation in the Milky Way; (2) diffusion of the galactic light above the galactic plane and in front of the large absorbing clouds; (3) the optical emission of the interstellar matter; (4) stars, and starlike objects with diameters less than 3 arc minutes. In the spectrometric mode (nebular spectrograph) the light from the center of the photometric field is concentrated on a slit covering 10 degrees by 10 arc minutes on the sky.

Courtes, G.↗