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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 577 records · Page 32
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NASA NTRS1986

Convection without eddy viscosity: An attempt to model the interiors of giant planets

In the theory of hydrostatic quasi-geostrophic flow in the Earth's atmosphere the principal results do not depend on the eddy viscosity. This contrasts with published theories of convection in deep rotating fluid spheres, where the wavelength of the fastest growing disturbance varies as E sup 1/3, where E, the Ekman number, is proportional to the eddy viscosity. A new theory of quasi-columnar motions in stably stratified fluid spheres attempts to capture the luck of the meteorologists. The theory allows one to investigate the stability of barotropic and baroclinic zonal flows that extend into the planetary interior. It is hypothesized that the internal heat Jupiter and Saturn comes out not radially but on sloping surfaces defined by the internal entropy distribution. To test the hypothesis one searches for basic states in which the wavelength of the fastest-growing disturbance remains finite as E tends to zero, and is which the heat flux vector is radially outward and poleward.

Ingersoll, A. P.↗
NASA NTRS1986

A proposal for adopting a standard coordinate system for defining atmospheric nomenclature for the giant planets

Although the albedo of specific belts and zones varies as a function of time, there is evidence that wind maxima may be fixed in latitude. Before considering a standard notation for wind jets, it is necessary to establish a coordinate system within which the nomenclature would be defined. Traditionally, the BAA has used planetographic latitudes; however, this system is based not only on an accurate determination of the polar diameter but also on the assumption that the equipotential surfaces can be represented by biaxial ellipsoids. The International Astronomical Union strives to adopt unambiguous nomenclature that will be universally acceptable. It is proposed that planetocentric coordinates be utilized and that a standardized value of the ratio of the polar diameter to the equatorial diameter be established for each planet to facilitate transformation into planetographic coordinates.

Beebe, R.↗
NASA NTRS1986

Giant impactors - Plausible sizes and populations

The largest sizes of planetesimals required to explain spin properties of planets are investigated in the context of the impact-trigger hypothesis of lunar origin. Solar system models with different large impactor sources are constructed and stochastic variations in obliquities and rotation periods resulting from each source are studied. The present study finds it highly plausible that earth was struck by a body of about 0.03-0.12 earth masses with enough energy and angular momentum to dislodge mantle material and form the present earth-moon system.

Hartmann, William K.↗
NASA NTRS1986

Dust grains and gas in the circumstellar envelopes around luminous red giant stars

Far-infrared color-color diagrams have been constructed for over 100 of the brightest evolved stars in the IRAS Point Source Catalog. The diagrams are used to deduce average values of the dust grain emissivity index (p) between 12 and 100 microns. Grains in C-rich and O-rich environments have similar values of p between 12 and 25 microns and between 60 and 100 microns, but between 25 and 60 microns p is larger by approximately 0.4 for the O-rich stars. Dust grains in envelopes around S-type stars seem to have 25 to 60 micron emissivities more nearly like grains in O-rich rather than C-rich environments. CO and HCN emissions from various stars are used to reclassify several stars as oxygen or carbon rich.

Zuckerman, B.↗
NASA NTRS1986

A theoretical and observational study of the Red Giant Branch phase transition in Magellanic Cloud clusters - A progress report

Preliminary results are reported for an investigation comparing theoretical models of the sudden appearance of an extended RGB (and its effects on the spectral energy distributions of stellar populations) with data from ESO CCD observations of clusters in the LMC and SMC. Isochrones for the entire RGB are being constructed on the basis of 100 new evolutionary sequences (calculated using the evolution code of Sweigart and Gross, 1976 and 1978) to permit determination of synthetic colors and spectral energy distributions. The observations so far indicate a main sequence about 0.1 mag redder than that predicted by the present models or by the isochrones of VandenBerg and Bell (1985), and fail to show a B-V color difference at the RGB phase transition.

Buonanno, R.↗
NASA NTRS1987

Mass-losing red giants in open clusters

Mass-losing stars in open clusters with main-sequence turn-offs at intermediate mass have been searched for by using the IRAS data base. The absence of many strong 60 micron sources in open clusters implies that intermediate-mass stars lose much of their mass during an intense wind phase of rather short duration. For stars of about seven solar masses, this phase, if it exists at all, lasts for not much more than 100,000 yr. For stars of about four solar masses, the intense wind phase appears to last considerably less than 10 million yr; it may well last for less than a million yr.

Jura, M.↗
NASA NTRS1986

Observational constraints on the interaction of giant molecular clouds with the solar system

The properties of the molecular cloud distribution are summarized, with special emphasis on the solar neighborhood. It is shown that the mass density within molecular clouds is sufficiently low that passing or grazing encounters cannot be significant in the perturbation of cometary orbits at 40,000 AU. The mean time for the sun between penetrating encounters of GMCs is about 1.5 Gyr with a typical duration of 1 Myr. The long time interval between encounters rules out a link between short-term periodicities in the geologic record and molecular cloud passages.

Scoville, N. Z.↗
NASA NTRS1987

The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

Roberts, William W., Jr.↗
NASA NTRS1988

The origin of the moon: Further studies of the giant impact

A number of technical improvements in the calculations which simulate the most violent event that has occurred to the earth during its history: its collision with the next largest body which was present in its region of accumulation in the early solar system, are discussed. This body was a planet in its own right, an object a little more massive than the planet Mars. The collision created a disk of molten and gaseous debris in orbit around the protoearth, and it is believed that the dissipation of this disk resulted in the formation of the moon. Also discussed is the serendipitous discovery that has emerged from the simulations: the role played by a huge, hot, rotating bar of rock and iron, which is formed immediately after the collision, in transferring angular momentum to much of the rock that is put into orbit, and in robbing the iron of angular momentum so that it falls promptly into the protoearth.

Benz, W.↗
NASA NTRS1987

Search for dark companions of K and M giants - Preliminary results for Alpha Boo

Preliminary results are presented for Alpha Boo, encompassing selected measurements during the period from January 1979 to June 1984. Four groups of data are chosen, each group taken within an interval of up to 1.5 months, and examined the internal consistency of each set to look for short term trends. The radial velocity was found to be very consistent with a standard deviation of about + or - 50 m/s within time scales of hours, days, and weeks. No significant radial velocity changes over these periods were detected. This suggests that the stellar surface activity is confined to the level of uncertainty. Because of this consistency it was possible to take the means of the radial velocity measurements within each group and compare them to look for possible long term changes. Variations of the radial velocity of about 200 m/s were found over the span of a few years, significant at the 6 to 8 sigma level.

Heyer, I.↗
NASA NTRS1987

Giant-scale supernova remnants - The role of differential galactic rotation and the formation of molecular clouds

The evolution of remnants produced by the total supernova power from an evolved OB association in a differentially rotating galactic disk is presented. The calculations at 5 kpc and 10 kpc from the galactic center lead to column densities across the remnant shell, or across sections of the remnants, which eventually exceed the opacity criterion of Franco and Cox (1986) and thus form molecular clouds. The resultant clouds have masses larger than 100,000 solar masses, dimensions of several hundred parsecs, and a separation larger than 1 kpc. In contrast, at 20 kpc from the galactic center the opacity criterion is never fulfilled.

Tenorio-Tagle, G.↗
NASA NTRS1988

The properties and environment of the giant, infrared-luminous galaxy IRAS 09104 + 4109

IRAS 09104 + 4109 is the most luminous object yet discovered by means of the IRAS survey. It is identified with a cD galaxy having a strong emission-line spectrum at a redshift of 0.442 and emits 6 x 10 to the 12th solar luminosities/sq h, 99 percent of which emerges at infrared wavelengths. One component of a double radio source is coincident with the center of the galaxy. The high luminosity of this source may be related to an interaction with one or more members of the rich cluster in which it lies. There is a secondary peak in the emission-line image of the galaxy. Emission lines from both regions are broad but narrower than those characteristic of the only other objects known to have such high luminosities, such as Seyfert 1's and QSOs. It is suggested that the strong infrared excess of IRAS 09104 + 4109 is produced by dust obscuring a broad line region.

Kleinmann, S. G.↗
NASA NTRS1988

Interiors of the giant planets

This theoretical/observational project constrains interior structure of Jovian planets through observational data. Researchers continue to concentrate on Neptune in support of the 1989 Voyager encounter. Occultations of stars by Neptune are observed from the Tucson area and from Chile to obtain information about Neptune's atmosphere and to continue to search for Neptune arcs. Occultations by other solar system objects are also observed as part of collaborative efforts from time to time. New results on the structure of scintillations in the central flash occultation by Neptune on 20 August 1985 were derived. Analysis shows that scintillations are present throughout the lightcurve, both near the half-intensity points (at a pressure of 1 microbar) and near the central flash (at 0.4 mbar). Near the planetary limb, the scintillations are extended parallel to the limb; near the shadow center, they are extended parallel to the limb; near the shadow center, they are extended in a radial direction. Researchers collaborated with Ramesh Narayan to derive a theory relating the scintillations to density fluctuations in Neptune's atmosphere. The theory will ultimately enable researchers to test whether the scintillations are caused by internal gravity waves in Neptune's upper atmosphere.

Hubbard, W. B.↗
NASA NTRS1989

Chromospherically active stars. VI - HD 136901 = UV CrB: A massive ellipsoidal K giant single-lined spectroscopic binary

The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 or larger. Additional constraints indicate that the secondary has a mass between 0.85 and 1.25 solar. Thus, the mass of the primary is at least 2.5 solar and probably is in the range 2.5-4 solar.

Fekel, Francis C.↗
NASA NTRS1989

Geochemical implications of the formation of the moon by a single giant impact

The origin of the moon by a single massive impact of a body slightly larger than Mars with the earth can explain the angular momentum, orbital characteristics and unique nature of the earth-moon system. The density and chemical differences between the earth and the moon are accounted for by deriving the moon from the mantle of the impactor. A cosmochemically plausible impactor can be formed in the region of the inner Solar System, lending support to the impact hypothesis.

Newsom, Horton E.↗
NASA NTRS1989

Buried topography of Utopia, Mars - Persistence of a giant impact depression

Knobs, partially buried craters, ring fractures, and some mesas permit a qualitative determination of the topography buried beneath younger northern plains materials. These features are widely distributed in the Utopia area but are absent in a large, roughly circular region centered at about 48 deg N, 240 deg W. This implies the existence of a circular depression about 3300 km in diameter buried beneath Utopia Planitia that is interpreted to represent the central part of a very large impact basin. The presence of buried curved massifs around part of this depression, and a roughly coincident mascon, lend further support. Present topography, areal geology, and paleotopography of buried surfaces all point to the persistence of this major depression for almost the entire history of Mars.

Mcgill, George E.↗
NASA NTRS1989

Dust-enshrouded asymptotic giant branch stars in the solar neighborhood

Using available infrared catalogs, an inventory is taken of the AGB star losing large amounts of mass within about 1 kpc of the sun. A surface density of these stars is estimated of about 25/sq kpc projected onto the plane of the Galaxy. Of these stars, about one-half are oxygen-rich while the other half are carbon-rich. The total mass-loss rate from AGB stars into the interstellar medium is probably between 3 and 6 x 10 to the -4th solar mass/sq kpc/yr. Within the uncertainties, this is in reasonable agreement with an estimated net loss rate of about 8 x 10 to the -4th solar mass/sq kpc/yr for main-sequence stars with initial masses between 1 and 5 solar masses as they evolve to white dwarfs. However, it is possible that there are important sources of mass loss which have not yet been identified. In the solar neighborhood, about one-half of all about 1.2 solar mass main-sequence stars spend greater than 30,000 yr in a carbon-star phase where they lose 1-2 x 10 to the -5th solar mass/yr and then become white dwarfs with about 0.7 solar mass.

Jura, M.↗
NASA NTRS1989

Theoretical studies of the infrared emission from circumstellar dust shells - The infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants

A simple analytic formula and a numerical radiative transfer program have been used to model the IR emission of spherically symmetric circumstellar dust shells in order to determine the IR absorption properties of circumstellar silicate grains and the mass-loss rates of the central stars. The correlation between the near-IR color temperature and the strength of the 10-micron emission or absorption feature is discussed, and it is shown that the near-IR absorption efficiency of circumstellar silicate grains is much higher than is expected from terrestrial minerals, possibly due to the presence of Fe(2+) color centers dissolved in the circumstellar silicates. Detailed models of the IR emission of R Cas, IRC 10011, and OH 26.5+0.6 are presented.

Schutte, W. A.↗