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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
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NASA NTRS1982

The circumstellar extinction of RY Sagittarii

In 1979-80, ultraviolet spectrophotometry of RY Sgr was obtained by the International Ultraviolet Explorer (IUE) during the star's recovery from its 1977-78 minimum. The wavelength dependence of the extinction of this R Coronae Borealis-type variable was determined by comparison of spectra obtained at different times but with nearly the same pulsational phase. The measured wavelength dependence is compatible with theoretical predictions of extinction by spherical graphite particles having a radius of 0.043 micron and with the extinction observed for amorphorus carbon smoke.

Holm, A. V.↗
NASA NTRS1982

Infrared/optical energy distributions of high redshifted quasars

Measurements at 1.2, 1.6 and 2.2 microns were combined with visual spectrophotometry of 21 quasars having redshifts z or = 2.66. The primary result is that the rest frame visual/ultraviolet continua of the high redshift quasars are well described by a sum of a power law continuum with slope of approximately -0.4 and a 3000 A bump. The rest frame visual/ultraviolet continua of these quasars are quite similar to that of 3C273, the archetype of low redshift quasars. There does not appear to be any visual/ultraviolet properties distinguishing high redshift quasars selected via visual or radio techniques.

Soifer, B. T.↗
NASA NTRS1983

Studies of planetary extended atmospheres

The light produced by the atoms and ions of Jupiter's luminous, heavy particle environment was studied. High resolution spectrophotometry is discussed.

Brown, R. A.↗
NASA NTRS1982

Mars: Definition and characterization of global surface units with emphasis on composition

Viking 2 approach maps of red and violet normal albedo are used to define units of similar optical properties for a large area of the Martian surface. Computer processing of these data reveals clusters of albedo values relating to specific, contiguous regions of the planet, with some unit boundaries being of a gradational nature while others are more discrete. A study of the albedo properties of analog materials measured in the laboratory, and of telescopic spectrophotometry of Mars, indicates that both hydroxylated and hematitic oxidized materials exist on the surface. The most probable surface expression of global dust and/or high albedo soils is in the classical bright region, Arabia. Most low albedo features in the region studied have red and violet albedos that are consistent with a dark substrate, such as basalt, coated by, or mixed with, a fine grained alteration product.

Mccord, T. B.↗
NASA NTRS1982

The outer satellites of Jupiter

Photometry and spectrophotometry of the Jovian outer satellites are used to throw light on the problem of their formation. The main plausible mechanisms for the formation of these satellites are discussd, including capture and breakup in the proto-Jovian nebula, collision within Jupiter's gravitational sphere of influence, and capture through the Jovian Lagrangian points after dissipation of the proto-Jovian nebula. UBV, VRI, and JHK color diagrams for various asteroids are used to show their similarity to the outer Jovian satellites. The evidence suggests that at least two outer Jovian satellites are comparable to C-type asteroids, and that two others are more nearly comparable to RD-type bodies. The apparent C-type satellites are both in the prograde cluster and the apparent RD-types are in the retrograde cluster. The Gradie and Veverka (1980) hypothesis that the reflectances and albedo characteristics of RD bodies may be due to aromatic kerogenlike compounds is discussed.

Cruikshank, D. P.↗
NASA NTRS1982

Diameters and albedos of satellites of Uranus

Products of the masses of the five known satellites of Uranus, and estimates of their bulk densities and surface albedos, are used to infer their probable dimensions. Spectrophotometry has established the presence of water ice on the surfaces of all save Rhea, and the brightnesses of the satellites have been measured photoelectrically. The diameter measurements presented were made using a photometric/radiometric technique, whose recent recalibration, using independent solar system object measurements, has yielded absolute accuracies better than 5 per cent. The new albedo measurements show that Umbriel, Titania and Oberon are similar to the Jupiter moon Callisto, while Ariel resembles the Saturn moon Hyperion. The diameters of all four are similar to those of the large, icy Saturn satellites Rhea and Iapetus.

Brown, R. H.↗
NASA NTRS1982

A search for frosts in Comet Bowell /1980b/

Infrared observations of Comet Bowell represent the first search for frost signatures in a comet beyond 2 AU from the sun. Broad- and narrowband photometry has been obtained as well as CVF spectrophotometry of this comet and there is no evidence for absorption features in the spectral area between 1.25 and 2.3 microns. Models of the coma have been generated which constrain the volatile content of the grains an; are in agreement with the observed albedo. The darkness of the coma particles at large heliocentric distances indicates a low albedo nucleus as well. Brightness variations during the observing period seem to indicate an active nucleus at 4.5 AU from the sun.

Campins, H.↗
NASA NTRS1983

Time-resolved ultraviolet and optical spectroscopy of the pulsating X-ray source H2252-035

UV spectrophotometry and and optical spectroscopy of H2252-035, a close binary featuring a spinning, magnetized star, were carried out with instrumentation on the IUE satellite, in addition to ground-based observations from the Lick Observatory. An excess reddening was determined, with E(B-V) equal to 0.10. The spectrum from 1200-22,000 A was decomposed into a blackbody with a temperature of 13,400 K and a power law wavelength component, where the exponent is 2.74, which fits the excess UV and IR excesses. The exponent value is noted to be amenable to a disk model with a slight curvature because of its finite extent. The emission-line intensities were found to vary by a factor of two, with some of the variations accountable by a modulation in-phase with the optical continuum binary modulation.

Cordova, F. A.↗
NASA NTRS1982

Cloud height differences on Saturn

Spectrophotometry from 0.6-2.5 micron at 1.5% spectral resolution of Saturn's equator and visibly dark South Equatorial Belt near a 1980 ring-plane crossing shows substantially less absorption by methane over the equator than over the SEB. Model fits using Appleby's model atmosphere and a multiple scattering model lead to the conclusion that the pressure levels of the clouds in the two regions differ by 20%. The region of high clouds is coincident with the location of the equatorial fast jet observed by Voyager.

Apt, J.↗
NASA NTRS1983

Velocity field and physical conditions in the active lenticular galaxy NGC 3998

A rotating and expanding flattened distribution of gas is suggested by measurements of the emission line velocity field for the line elliptical/lenticular galaxy NGC 3998, using seven long slit spectrograms in five position angles. Expanding material kinetic energy values of 10 to the 53rd to 10 to the 54th ergs, together with the flat spectrum radio source and nucleus X-ray emission, indicate pronounced nuclear activity. Spectrophotometry of the galactic nucleus shows emission line strengths typical of shocks rather than of photoionization, and line ratios indicate a postshock temperature of 60,000 K and a preshock density of 25 particles/cu cm. Both the stars and the ionized gas of the galaxy have central velocity dispersions of 260 km/s. In view of the high rotational velocity of the stars, NGC 3998 is a lenticular rather than elliptical galaxy.

Blackman, C. P.↗
NASA NTRS1983

The albedo of Uranus

New absolute spectrophotometry of Uranus between 3295 A and 7676 A obtained at spectral resolutions of 4 A and 8 A during its 1981 apparition is reported and compared with previous observations by Younkin (1970) recorded during the 1961-1963 apparitions. Geometric albedos are calculated, and Bond albedos are estimated for both sets of data. An increase in brightness of about 14% and a color change occurred during the interval between the epochs of observation, consistent with the high north-polar haze reported by Price and Franz (1979) and the change in aspect of the planet. An upper limit to the internal heat source is estimated from energy balance considerations.

Lockwood, G. W.↗
NASA NTRS1983

Eight-color photometry of Hyperion, Iapetus, and Phoebe

The Phoebe, Hyperion and Iapetus Saturn satellites are discussed in light of eight-color spectrophotometry, which together with observed V magnitudes and Voyager spacecraft-derived diameters yields geometric albedos of 0.07 for Iapetus, 0.06 for Phoebe, and maximum- and minimum-dimension based limits of 0.19 and 0.25 respectively for Hyperion. While both Hyperion and Iapetus have similar, very reddish spectra, it is noted that Hyperion has a much higher albedo than the dark side of Iapetus. The mean spectrum of Phoebe is much flatter, with a broad absorption feature near 1 micron. The determination of these optical differences between the surface materials of Phoebe and the dark side of Iapetus constrains the possible interaction modes between Phoebe and the other two satellites.

Tholen, D. J.↗
NASA NTRS1983

The red edge of plant leaf reflectance

A detailed study of the red edge spectral feature of green vegetation based on laboratory reflectance spectrophotometry is presented. A parameter lambda is defined as the wavelength is defined as the wavelength of maximum slope and found to be dependent on chlorophyll concentration. Species, development stage, leaf layering, and leaf water content of vegetation also influences lambda. The maximum slope parameter is found to be independent of simulated ground area coverage. The results are interpreted in terms of Beer's Law and Kubelka-Munk theory. The chlorophyll concentration dependence of lambda seems to be explained in terms of a pure absorption effect, and it is suggested that the existence of two lambda components arises from leaf scattering properties. The results indicate that red edge measurements will be valuable for assessment of vegetative chlorophyll status and leaf area index independently of ground cover variations, and will be particularly suitable for early stress detection.

Horler, D. N. H.↗
NASA NTRS1983

The C2H, C2, and CN electronic absorption bands in the carbon star HD 19557

Infrared spectrophotometry of the R-type carbon star HD 19557 is presented. Two unusual spectroscopic features are seen: a 3.1 micron band is lacking and a 2.8 micron band is present. Identifications are proposed for three previously unreported stellar absorption bands with electronic sequences of C2, CN, and C2H. The latter is proposed to be responsible for the 2.8 micron feature. The atmospheric structure of the star is studied with synthetic spectra, and an effective temperature between 2600 K and 3000 K is suggested. No SiC emission is seen at 11.3 microns, indicating that grain formation is not a viable process around the star. The lack of dust in R stars may suggest a salient difference between R and N types.

Goebel, J. H.↗
NASA NTRS1983

The Uranian satellites - Surface compositions and opposition brightness surges

The present, 5 percent-resolution spectrophotometry for the Uranian satellites Ariel, Umbriel, Titania and Oberon cover the 1.43-2.57 wavelength region and confirm the presence of a spectrally dominant water ice component in their surfaces. The 1.5- and 2.0-micron water absorption band depths and continuum reflectance indicate significant differences among the surface compositional properties of the four satellites, and comparisons of the spectra with those of other solar system bodies and of laboratory water ice spectra imply the presence of a significant nonwater ice component on/in their surfaces. The nature of this nonwater ice component is suggested by the data to be similar to that of such substances as carbon black. Near-IR opposition brightness surges of Ariel, Titania and Oberon are found to be among the largest in the solar system.

Brown, R. H.↗
NASA NTRS1984

Determination of the succinonitrile-benzene and succinonitrile-cyclohexanol phase diagrams by thermal and UV spectroscopic analysis

Equilibrium temperature-composition diagrams were determined for the two organic systems, succinonitrile-benzene and succinonitrile-cyclohexanol. Measurements were made using the common thermal analysis methods and UV spectrophotometry. Succinonitrile-benzene monotectic was chosen for its low affinity for water and because UV analysis would be simplified. Succinonitrile-cyclohexanol was chosen because both components are transparent models for metallic solidification, as opposed to the other known succinonitrile-based monotectics.

Kaukler, W. F.↗
NASA NTRS1984

New infrared observations of IRS1, IRS3 and the adjacent nebula in the OMC-2 cluster

Near infrared reflection nebulae are often observed around embedded protostellar objects. New observations of the infrared cluster of low luminosity protostars in Orion Molecular Cloud 2 (OMC2) are reported. The asymmetric distribution of the extended emission seen about IRS1 is in fact another infrared reflection nebulae. Observations of near infrared polarimetry, photometry, and spectrophotometry were carried out.

Pendleton, Y.↗
NASA NTRS1984

Earth-Based Planetary Data

NASA sponsors Earth-based planetary astronomy to provide data needed for: planning future missions; supporting missions already in progress; and enhanching the scientific analysis of data returned by past missions. Such data complement spacecraft data by providing observational coverage of important planetary phenomena at epochs before and after spacecraft encounters, with time scales longer than a spacecraft encounter, and at wavelengths and spectral resolutions not covered by spacecraft instruments. Earth-based planetary data are defined here as: observations made with ground based telescopes, balloon-borne instruments, rocket-borne instruments, and Earth-orbiting spacecraft. Data in the last category differ somewhat in nature and availability from the other three. In all categories, planetary data are only a subset of the total astronomical observations on record. As a result part of the task is to identify and extract (or separately catalog) those observations which are planetary. The data cover wavelengths in the ultraviolet, the visual, and the infrared. The instrumental techniques addressed are: imaging, polarimetry, photometry, spectrophotometry, and spectroscopy.

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