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At least 829 records · Page 46

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NASA NTRS1978

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

Pollard, D.↗

NASA NTRS1978

Viking Orbiter stereophotogrammetry

Orbit characteristics of the two Viking Orbiter spacecraft made possible the acquisition of high-resolution imagery of the Martian surface, resulting in many excellent convergent stereopairs. Evaluation of these stereopairs presented a few unconventional problems because the routine relative orientation was not feasible, mainly due to a lack of good passpoints and to the technical peculiarities of TV vidicon imaging techniques. One of the ways to circumvent these problems is to use the orbital and navigational parameters of the spacecraft for an external 'forced' relative orientation. This approach requires a number of rotations and counter-rotations between various coordinate systems, which may make the involved mathematics look rather complicated, but its computational applications become very simple, fast, accurate, and inexpensive.

Benesh, M.↗

NASA NTRS1978

A model of V356 Sagittarii

It is pointed out that V356 Sgr is an abnormal member of the Algol class of binaries. According to Popper (1955), the primary component is of spectral type B3V and is rotating rapidly, while the secondary is of type A2II and is rotating at least approximately in synchronism with the orbital motion. The system is either semidetached or quite near to being semidetached. The main anomalies are related to the ratio of eclipse depths, the very small reflection effect of the light curves, differences between the duration of the primary and the secondary eclipse, and the unusual characteristics of the primary eclipse. It is concluded that the lack of agreement between theory and observation can be due only to an important attribute of the binary which has not yet been incorporated into the theory. The peculiarities can most reasonably be explained in terms of a geometrically and optically thick disk which surrounds the primary component.

Wilson, R. E.↗

NASA NTRS1978

Positions of galactic X-ray sources with l/II/ between -20 deg and +6 deg

The precise positions of nine X-ray sources in the vicinity of the galactic center are reported. The data were obtained as part of the comprehensive survey of the galactic plane performed with the rotating modulation collimator detectors on the SAS-3 X-ray observatory. The sources include the binary X-ray source 4U 1700-37 which has a well established optical counterpart that lies 7 sec from the reported position. The other sources GX 349+2, 4U 1702-42, 4U 1705-44, MX 1716-31, A 1742-294, 4U 1755-33, GX 5-1, and 2S 1803-245 lack established counterparts in other wavelengths. The obtained position for GX 5-1 adds confidence to the radio counterpart proposed by Braes et al. (1972). The reported position for 4U 1755-33 excludes the optical counterpart proposed by Jones et al. (1974).

Jernigan, J. G.↗

NASA NTRS1978

On the rotation of elliptical galaxies

The tensor virial theorem is applied to models of early-type galaxies. First the theorem is applied to rotating elliptical galaxies whose constant-density surfaces are similar ellipsoids. A relationship is obtained between the observed rotations and the forms of generally triaxial galaxies. By applying the results of Robert (1962) to the evaluation of the components of the Chandrasekhar tensor which occurs in this relationship, it is found that the form of a galaxy that lacks global velocity anisotropy uniquely determines the ratio of its rotational and random kinetic energies independently of the radial density profile of that galaxy. A distribution of three-dimensional prolate spheroids is derived which accounts for the observed distribution of ellipticities reported by Sandage, Freeman, and Stokes (1970). This is then used to derive curves giving the expected frequency of occurrence of galaxies of given rotational velocities for each of a number of different apparent elongations on the sky. It is found that if elliptical galaxies are prolate, there should be little correlation between apparent ellipticity and rotation velocity.

Binney, J.↗

NASA NTRS1978

Dayside auroral arcs and convection

Recent Defense Meteorological Satellite Program and International Satellite for Ionospheric Studies dayside auroral observations show two striking features: a lack of visible auroral arcs near noon and occasional fan shaped arcs radiating away from noon on both the morning and afternoon sides of the auroral oval. A simple model which includes these two features is developed by reference to the dayside convection pattern of Heelis et al. (1976). The model may be testable in the near future with simultaneous convection, current and auroral light data.

Reiff, P. H.↗

NASA NTRS1978

The driving force for magnetospheric convection

Viscously driven magnetospheric models, as well as a model involving interconnection between the geomagnetic field and the magnetic field in the solar wind, have been proposed to describe the driving force for magnetospheric convection. Lack of a satisfactory theory for the interconnection in the latter model and, in the case of the viscous interaction models, inadequacies in predicting the quantity of the driving force, make these two classes of models less than successful. Accordingly, a mechanically driven magnetospheric model is proposed: solar wind plasma enters the magnetosphere around the neutral points, covers the inner surface of the magnetopause and subsequently expands, driving convection as it escapes from the open tail.

Johnson, F. S.↗

NASA NTRS1978

Limb brightening on Uranus - The visible spectrum. II

A detailed analysis is presented of photoelectric area-scanning photometry of the Uranus disk obtained during the 1976 apparition. Coarse quantitative information on the true radial intensity distribution over the Uranus disk is derived in four selected wavebands. Lack of circular symmetry in the intensity distributions indicates the presence of disk structure, especially polar brightening, in each waveband. For the 6190-A CH4 band, the distribution corresponds to a uniform disk upon which a hint of polar brightening is superimposed. For the 6400-A region, moderate limb darkening is found. It is pointed out that the coarse analytical technique used in the analysis to explore the information content of the photometric scans of Uranus has several basic limitations. Direct deconvolution of the Uranus scans is required to thoroughly investigate the two-dimensional photometric structure of its disk.

Price, M. J.↗

NASA NTRS1978

Stellar model chromospheres. VIII - 70 Ophiuchi A /K0 V/ and Epsilon Eridani /K2 V/

Model atmospheres for the late-type active-chromosphere dwarf stars 70 Oph A and Epsilon Eri are computed from high-resolution Ca II K line profiles as well as Mg II h and k line fluxes. A method is used which determines a plane-parallel homogeneous hydrostatic-equilibrium model of the upper photosphere and chromosphere which differs from theoretical models by lacking the constraint of radiative equilibrium (RE). The determinations of surface gravities, metallicities, and effective temperatures are discussed, and the computational methods, model atoms, atomic data, and observations are described. Temperature distributions for the two stars are plotted and compared with RE models for the adopted effective temperatures and gravities. The previously investigated T min/T eff vs. T eff relation is extended to Epsilon Eri and 70 Oph A, observed and computed Ca II K and Mg II h and k integrated emission fluxes are compared, and full tabulations are given for the proposed models. It is suggested that if less than half the observed Mg II flux for the two stars is lost in noise, the difference between an active-chromosphere star and a quiet-chromosphere star lies in the lower-chromospheric temperature gradient.

Kelch, W. L.↗

NASA NTRS1978

Interhemispheric gradients of CF2Cl2, CFCl3, CCl4, and N2O

Direct real-time gas-chromatographic measurements of CF2Cl2, CFCl3, CCl4, and N2O were made at latitudes from 74 deg N to 62 deg S aboard a NASA Convair 990 as part of the 1976 NASA CV-990 Latitude Survey Mission between Alaska and New Zealand. A difference was found in the average mixing ratios of CF2Cl2 and CFCl3 between the Northern and Southern Hemispheres, but no differences were noted for CCl4 and N2O. The results support some of the previous studies of interhemispheric tropospheric gradients and suggest the lack of any significant tropospheric sinks.

Tyson, B. J.↗

NASA NTRS1977

Lightcurve analyses for 170 small asteroids

Small asteroids, with sizes of about 1 km, appear to rotate faster than do the larger, about 200 km, asteroids. There is a lack of highly elongated objects, probably due to a collisional erosion process in the main asteroid belt.

Degewij, J.↗

NASA NTRS1977

Comparison of orbital chemistry with crustal thickness and lunar sample chemistry

A correlation between orbital chemistry (FeO, Al2O3, Mg/Al, MgO/FeO, Th) and the lunar crustal thickness is examined. The correlation suggests either lack of complete homogenization by lateral or vertical mixing, or lateral variation in the differentiation process. In addition, links between orbital chemistry and lunar sample chemistry are investigated. In regions with crustal thickness between 100 and 110 km, gabbroic anorthosites are very abundant, while in regions with crustal thickness of about 80 km anorthositic gabbros are frequent. Special attention is given to the distribution of low-potassium Fra Mauro basalt, found in high concentrations in regions with 50 to 60 km crustal thickness.

Schonfeld, E.↗

NASA NTRS1977

Evolution of KREEP - Further petrologic evidence

It is hypothesized that KREEP samples from the Apollo 15 site are igneous. To support the hypothesis, comparisons are made with other crystalline KREEP samples, especially 14310. It is noted that the low siderophile element content and lack of high pressure phenocrysts in the Apollo 15 KREEP may be indications of a slower rise of KREEP melt to the surface, when contrasted with sample 14310. Gravitational separation of Fe-Ni metal is proposed as a mechanism to account for the depletion of siderophile elements relative to the Si-rich component. It is further suggested that KREEP may be the parent of Apollo 12 and 15 basalts, as well as of granitic rocks, due to the liquid immiscibility occurring during the KREEP melt crystallization, and the subsequent independent evolution of the components.

Crawford, M. L.↗

NASA NTRS1977

Apollo 17 ropy glasses

Ropy glasses are a major soil component in the Apollo 17 gray soils 74240 and 74260. These particles form a distinct morphological type characterized by a wide range of dynamic shapes with a diagnostic sorted and welded fine-grained debris coating. Apollo 17 ropy glasses show abundant evidence for shock. Shocked lithic and mineral inclusions, lack of any igneous textures, and lechatelierite, all indicate an impact origin. A striking similarity is observed between the lunar ropy glasses and the glass impact bombs (Flaedle) of the Ries Crater in Germany. A highland basaltic composition was observed for the Apollo 17 ropy glasses in contrast to the KREEP composition of ropy glasses from the Apollo 12 and Apollo 14 landing sites. Other workers have presented convincing evidence that ejecta from Tycho reached the Taurus-Littrow Valley, and these ropy glasses may represent Tycho ejecta. However, the close stratigraphic association of the ropy glasses with the greater than 3.5 b.y. old orange glass suggests the ropy glasses may be too old to be Tycho ejecta, which should be only about 100 m.y. old. If this is the case, the ropy glasses represent impact glasses from a very old impact in an unknown highlands source area.

Fruland, R. M.↗

NASA NTRS1978

California's geothermal resource potential

According to a U.S. Geological Survey estimate, recoverable hydrothermal energy in California may amount to 19,000 MW of electric power for a 30-year period. At present, a geothermal installation in the Geysers region of the state provides 502 MWe of capacity; an additional 1500 MWe of electric generating capacity is scheduled to be in operation in geothermal fields by 1985. In addition to hydrothermal energy sources, hot-igneous and conduction-dominated resources are under investigation for possible development. Land-use conflicts, environmental concerns and lack of risk capital may limit this development.

Leibowitz, L. P.↗

NASA NTRS1978

Observations of low-luminosity X-ray sources in Vela-Puppis

Results are presented for a study of the X-ray emission from a small portion of the galactic plane near galactic longitude 260 deg. This region contains at least six low-luminosity X-ray sources within about 10 deg of PSR 0833-45, which is near the center of the Gum nebula. The X-ray source 4U 0833-45, associated with the Vela pulsar, is observed at twice its 4U catalog intensity. The lack of X-ray pulsations at the pulsar period (greater than 99% nonpulsed), the nonthermal power-law spectrum, and models of the X-ray source distribution in this region suggest that a large fraction of the X-rays come from an extended source about 1 deg of arc in radius. The observation of a high-temperature (effective temperature at least 100 million K) spectrum in a field of view containing only Puppis A among known sources has led to the discovery of new OSO 8 source, OS 0752-39. Other spectra from this region are discussed.

Pravdo, S. H.↗

NASA NTRS1977

A model for wind-extension of the Copernicus ejecta blanket

The interaction between crater ejecta and the transient wind from impact-shock vaporization is discussed. Based partly on Shoemaker's (1962) ballistic model of the Copernicus ejecta and partly on Rehfuss' (1972) treatment of lunar winds, a simple model is developed which indicates that if Copernicus were formed by a basaltic meteorite impacting at 20 km/s, then 3% of the ejecta mass would be sent beyond the maximum range expected from purely ballistic trajectories. That 3% mass would, however, shift the position of the outer edge of the ejecta blanket more than 400% beyond the edge of the ballistic blanket. For planetary bodies lacking an intrinsic atmosphere, the present model indicates that this form of hyperballistic transport can be very significant for small (no more than about 1 kg) ejecta fragments.

Rehfuss, D. E.↗

NASA NTRS1975

Minor elements in lunar olivine as a petrologic indicator

Accurate electron microprobe analyses (approximately 50 ppm) were made for Al, Ca, Ti, Cr, Mn, and Ni in Mg-rich olivines which may derive from early lunar crust or deeper environments. Low-Ca contents consistently occur only in olivines from dunitic and troctolitic breccia: spinel troctolite and other rock types have high-Ca olivines suggesting derivation by near-surface processes. Rock 15445 has olivine with distinctly low CaO (approximately 0.01 wt.%). Chromium ranges to higher values (max.0.2 oxide wt.%) than for terrestrial harzburgites and lherzolites but is similar to the range in terrestrial komatiites. Divalent chromium may be indicated over trivalent Cr because olivines lack sufficient other elements for charge balance of the latter. NiO values in lunar specimens range from 0.00 to 0.07 wt.% and a weak anticorrelation with Cr2O3 suggests an oxidation state effect. Al2O3 values are mostly below 0.04-wt.% and show no obvious correlation with fragment type. TiO2 values lie below 0.13-wt.% and seem to correlate best with crystallization rate and plagioclase content of the host rock. High values of Al2O3 and TiO2 reported by other workers have not been confirmed, and are probably wrong.

Steele, I. M.↗