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At least 469 records · Page 26
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NASA NTRS1992

A prediction of the gamma-ray flux from Nova Herculis 1991

UV observations made with the IUE satellite of Nova Her 1991 are presented and discussed. A distance of 3.4 kpc and reddening of 0.6 E(B-V) to Nova Her 1991 are determined by comparing its UV and optical outburst behavior with those of the extragalactic ONeMg nova LMC 1990 No. 1. Her 1991 was also detected by Rosat five days into its outburst, and it is argued that a small fraction of the X-rays may be the product of Comptonized 1.2 and 0.5 MeV emission from the decay of Na-22. If the mass of ejected shell is indeed as high as was estimated by Woodward et al. (1992), namely 0.0001 solar mass, then the present results predicted that Na-22 gamma-ray emission from the ejecta of Nova Her 1991 would still be detectable by GRO in the spring of 1992. The detection level was expected to be about 5 sigma in a two-week observation. Such a detection would strongly guide and constrain the hydrodynamic and nucleosynthesis simulations of nova outbursts on massive white dwarfs.

Starrfield, Sumner↗
NASA NTRS1992

High-velocity interstellar gas toward HD 169454

The interstellar spectrum of HD 169454 reveals Na D and Ca K absorption at about + 100 km/s. Measurements made at high resolution resolve 4 narrow (about 2-3 km/s) features whose N(Ca II)/N(Na I) ratios are small. This high-velocity gas is, therefore, unique in that it resembles local quiescent gas, not shocked gas. Redshifted gas is also seen in moderate-resolution spectra of faint stars lying in the same portion of the sky as HD 169454. The resulting picture is one in which a supernova explosion or stellar winds within the Sct OB3 association at a distance of about 1.5 kpc is pushing quiescent gas away from the sun. The gas is seen only in stars estimated to be at most 3 kpc, but greater than 2 kpc, away. If HD 169454 is at this greater distance, its absolute magnitude would be about -9, making it the second most luminous B star in the Galaxy.

Federman, S. R.↗
NASA NTRS1991

Bifunctional alkaline oxygen electrodes

The authors describe the identification and testing of electrocatalysts and supports for the positive electrode of moderate-temperature, single-unit, rechargeable alkaline fuel cells. Recent work on Na(x)Pt3O4, a potential bifunctional catalyst, is described, as well as the application of novel approaches to the development of more efficient bifunctional electrode structures. The three dual-character electrodes considered here showed similar superior performance; the Pt/RhO2 and Rh/RhO2 electrodes showed slightly better performance than the Pt/IrO2 electrode. It is concluded that Na(x)Pt3O4 continues to be a promising bifunctional oxygen electrode catalyst but requires further investigation and development.

Swette, L.↗
NASA NTRS1992

Lunar mining of oxygen using fluorine

An important aspect of lunar mining will be the extraction of volatiles, particularly oxygen, from lunar rocks. Thermodynamic data show that oxygen could readily be recovered by fluorination of abundant lunar anorthite, CaAl2Si2O8. Fluorine is the most reactive element, and the only reagent able to extract 100 percent of the oxygen from any mineral, yet it can safely be stored or reacted in nickel or iron containers. The general fluorination reaction, mineral + 2F2 = mixed fluorides = O2, has been used for more than 30 years at a laboratory scale by stable-isotope geochemists. For anorthite, metallic Al and Si may be recovered from the mixed fluorides by Na-reduction, and CaO via exchange with Na2O; the resulting NaF may be recycled into F2 and Na by electrolysis, using lanthanide-doped CaF2 as the inert anode.

Burt, Donald M.↗
NASA NTRS1992

Lunar and Asteroid Composition Using a Remote Secondary Ion Mass Spectrometer

Laboratory experiments simulating solar wind sputtering of lunar surface materials have shown that solar wind protons sputter secondary ions in sufficient numbers to be measured from low-altitude lunar orbit. Secondary ions of Na, Mg, Al, Si, K, Ca, Mn, Ti, and Fe have been observed sputtered from sample simulants of mare and highland soils. While solar wind ions are hundreds of times less efficient than those used in standard secondary ion mass spectrometry, secondary ion fluxes expected at the Moon under normal solar wind conditions range from approximately 10 to greater than 10(exp 4) ions cm(sup -2)s(sup -1), depending on species. These secondary ion fluxes depend both on concentration in the soil and on probability of ionization; yields of easily ionized elements such as K and Na are relatively much greater than those for the more electronegative elements and compounds. Once these ions leave the surface, they are subject to acceleration by local electric and magnetic fields. For typical solar wind conditions, secondary ions can be accelerated to an orbital observing location. The same is true for atmospheric atoms and molecules that are photoionized by solar EUV. The instrument to detect, identify, and map secondary ions sputtered from the lunar surface and photoions arising from the tenuous atmosphere is discussed.

Elphic, R. C.↗
NASA NTRS1993

Nuclear and large-scale outflow in NGC 1808

NGC 1808 has been studied via deep broad-band and H-alpha images and longslit spectroscopy around the Na I D and H-alpha lines. In particular, Na I is seen blueshifted in absorption and redshifted in emission, providing incontrovertible proof of outflow. B-R images show that the dust plumes associated with the outflow reach about 3 kpc or more above the plane. The morphology of the outflow is complex. Nuclear emission and absorption line profiles show pronounced blue wings similar to those seen in far-IR luminous galaxies (FIRGs), and indicate nuclear outflow velocities up to 700 km/s. The classification of NGC 1808 as a Seyfert 2 is reviewed and dismissed; rather, on the basis of line profiles and ratios and the presence of the 'superwind', NGC 1808 is probably an example of the FIRG phenomenon.

Phillips, Andrew C.↗
NASA NTRS1992

The equilibrium of atmospheric sodium

We now have four examples of planetary objects with detectable sodium (and potassium) in their atmospheres: Earth, Io, Mercury and the moon. After a summary of the observational data, this survey discusses proposed sources and sinks. It appears that Io's surface material is rich in frozen SO2, but with around 1 percent of some sodium compound. The Io plasma torus contains ions of S, O and Na, also with at least one molecular ion containing Na. In turn, impact by these ions probably sustains the torus, as well as an extended neutral corona. A primary source for the Earth, Mercury and the moon is meteoroidal bombardment; at Mercury and perhaps the moon it may be supplemented by degassing of atoms from the regolith. Photoionization is important everywhere, although hot electrons are dominant at Io.

Hunten, Donald M.↗
NASA NTRS1992

Design and analysis of soft X-ray imaging microscopes

The spherical Schwarzschild microscope for soft X-ray applications in microscopy and projection lithography consists of two concentric spherical mirrors configured such that the third-order spherical aberration and coma are zero. Since multilayers are used on the mirror substrates for X-ray applications, it is desirable to have only two reflecting surfaces in a microscope. To reduce microscope aberrations and increase the field of view, generalized mirror surface profiles are here considered. Based on incoherent and sine wave modulation transfer function calculations, the object plane resolution of a microscope has been analyzed as a function of the object height and numerical aperture (NA) of the primary for several spherical Schwarzschild, conic, and aspherical Head reflecting two-mirror microscope configurations. The Head microscope with a NA of 0.4 achieves diffraction limited performance for objects with a diameter of 40 microns. Thus, it seems possible to record images with a feature size less than 100 A with a 40x microscope when using 40 A radiation.

Shealy, David L.↗
NASA NTRS1993

High-resolution Ca II observations of the local interstellar medium

High-resolution absorption measurements of the interstellar Ca II K line observed toward 46 early-type stars in the local ISM (LISM) are presented. Ca II was detected in 36 of the 46 stars with 82 individual cloud components identified. Ca II was detected to most of the stars closer than 50 pc, except in the region of the Galactic quadrant l = 180-270 degrees which also contains the empty line of sight to B CMa at 220 pc. The mean local standard of rest velocity of the 82 Ca II components implies that the LISM clouds are associated with the motion of the solar neighborhood and not the sun. If the present data are combined with other nearby Ca II component velocities taken from the literature, then a cloud centered approximately at l = 90 deg, b = -40 deg moving coherently with the local interstellar wind vector is supported at a significance level of 99 percent. The Ca II data have been combined with Na I data for the same stars to produce a N(Na I)/N(Ca II) ratio for each identified absorption feature. This ratio plotted against the local standard of rest velocities of the clouds shows that the Routly-Spitzer effect exists down to +/- 10 km/s, which supports grain desorption/destruction models that are efficient at returning calcium to the gas phase at these low velocities.

Vallerga, J. V.↗
NASA NTRS1994

Alkali element depletion by core formation and vaporization on the early Earth

The depletion of Na, K, Rb, and Cs in the Earth's upper mantle and crust relative to their abundances in chondrites is a long standing problem in geochemistry. Here we consider two commonly invoked mechanisms, namely core formation, and vaporization, for producing the observed depletions. Our models predict that a significant percentage of the Earth's bulk alkali element inventory is in the core (30 percent for Na, 52 percent for K, 74 percent for Rb, and 92 percent for Cs). These predictions agree with independent estimates from nebular volatility trends and (for K) from terrestrial heat flow data. Our models also predict that vaporization and thermal escape during planetary accretion are unlikely to produce the observed alkali element depletion pattern. However, loss during the putative giant impact which formed the Moon cannot be ruled out. Experimental, observational, and theoretical tests of our predictions are also described. Alkali element partitioning into the Earth's core was modeled by assuming that alkali element partitioning during core formation on the aubrite parent body (APB) is analogous to that on the early Earth. The analogy is reasonable for three reasons. First, the enstatite meteorites are the only known meteorites with the same oxygen isotope systematics as the Earth-Moon system. Second, the large core size of the Earth and the V depletion in the mantle requires accretion from planetesimals as reduced as the enstatite chondrites. Third, experimental studies of K partitioning between silicate and metal plus sulfide show that more K goes into the metal plus sulfide at higher pressures than at one atmosphere pressure. Thus partitioning in the relatively low pressure natural laboratory of the APB is a good guide to alkali elemental partitioning during the growth of the Earth.

Lodders, K.↗
NASA NTRS1994

Constraints placed on the chondrule-forming process by merrihueite in the Mezoe-Madaras chondrite

A few unusual chondrules in the Mezoe-Madaras L3 chondrite contain the peralkaline mineral merrihueite, (K, Na)2(Fe, Mg)5Si12O30, formed by reaction of free silica in the chondrules with K, Na, Fe-rich nebular gas. Vapor fractionation was required to create chondrules poor in Al and rich in Si, and the fractionated condensate produced had to aggregate into protochondrules very promptly (on the order of hours or less) to prevent it from mixing with dust of more generalized composition in the nebula. The traditional paradigm for chondrule formation, involving a series of unrelated events (chemical fractionation of precursor dust; clumping of the dust; melting of the dust-clumps), is inadequate for making these chondrules. A rapid process, all stages of which are related, is required. We propose that this occurred during the cooling and contraction of the volume of hot gas created by a small transient high-energy event in the nebula, of unspecified nature. Microdroplets of silicate melt created by condensation from the cooling, contracting gas had velocity vectors directed toward the center of the volume. Coalescence occurred in the crowded central zone where the microdroplets converged. The Mezoe-Madaras merriihueite-bearing chondrules may have been formed by an atypically low-energy nebular event, which achieved the needed chemical fractionations by only partially vaporizing precursor dust. More commonplace chondrule types may have been created by the same basic process, but involving higher-energy events in which precursor dust was completely vaporized and recondensed.

Wood, John A.↗
NASA NTRS1994

Extreme ultraviolet explorer satellite observation of Jupiter's Io plasma torus

We present the first Extreme Ultraviolet Explorer (EUVE) satellite observation of the Jupiter system, obtained during the 2 day period 1993 March 30 through April 1, which shows a rich emission-line spectrum from the Io plasma torus spanning wavelengths 370 to 735 A. The emission features correspond primarily to known multiplets of oxygen and sulfur ions, but a blended feature near 372 A is a plausible Na II transition. The summed detected energy flux of (7.2 +/- 0.2) x 10(exp -11) ergs/sq cm(s) corresponds to a radiated power of approximately equal to 4 x 10(exp 11) W in this spectral range. All ansa emissions show a distinct dawn-dusk brightness asymmetry and the measured dusk/dawn ratio of the bright S III lambda-680 feature is 2.3 +/- 0.3, significantly larger than the ratio measured by the Voyager spacecraft ultraviolet (UV) instruments. A preliminary estimate of ion partitioning indicates that the oxygen/sulfur ion ratio is approximately equal to 2, compared to the value approximately equal to 1.3 measured by Voyager, and that (Na(+))/(e) greater than 0.01.

Hall, D. T↗
NASA NTRS1994

Glass-rich chondrules in ordinary chondrites

There are two types of glass-rich chondrules in unequilibrated ordinary chondrites (OC): (1) porphyritic chondrules containing 55-85 vol% glass or microcrystalline mesostasis and (2) nonporphyritic chondrules, containing 90-99 vol% glass. These two types are similar in mineralogy and bulk composition to previously described Al-rich chondrules in OC. In addition to Si-, Al- and Na-rich glass or Ca-Al-rich microcrystalline mesostasis, glass-rich chondrules contain dendritic and skeletal crystals of olivine, Al2O3-rich low-Ca pyroxene and fassaite. Some chondrules contain relict grains of forsterite +/- Mg-Al spinel. We suggest that glass-rich chondrules were formed early in nebular history by melting fine-grained precursor materials rich in refractory (Ca, Al, Ti) an moderately volatite (Na, K) components (possibly related to Ca-Al-rich inclusions) admixed with coarse relict forsterite and spinel grains derived from previously disrupted type-I chondrules.

Krot, Alexander N.↗
NASA NTRS1995

High-velocity, high-excitation neutral carbon in a cloud in the Vela supernova remnant

HD 72089 is situated behind the Vela supernova remnant, and the interstellar absorption lines in the spectrum of this star are remarkable for two reasons. First, there are six distinct velocity components that span the (heliocentric) velocity range -60 to +121 km/s in the lines of Na I and Ca II. Second, two of the components at high velocity, one at +85 km/s and another at +121.5 km/s, have densities that are large enough to produce observable lines from neutral carbon. The gas moving at +121.5 km/s has such a large pressure that the excited fine-structure levels of the ground electronic state of C I are collisionally populated nearly in proportion to their level degeneracies. This high-velocity gas exhibits unusually low column densities of Mg I and Na I, compared to that of C I. We propose that the +121.5 km/s component represents gas that has cooled and recombined in a zone that follows a shock driven into a cloud by the very recent passage of a supernova blast wave. A representative preshock density of n(sub H) approximately = 13/cc and velocity v(sub s) = 100 km/s is indicated by the strength of diffuse (O III) emission lines seen in directions very near HD 72089. The strong collisional population of excited C I and apparent absence of excited levels of O I give a most favorable fit to the conditions 1000 less than n(sub H) less than 2900/cc over a temperature range 300 less than T less than 1000 K. The fact that the compression is not substantially more than this indicates that the preshock gas may have had an embedded, transverse magnetic field with a strength B greater than or approximately = 1 micro-G. The large dynamical pressure of the supernova blast wave that would be needed to create the cloud shock that we describe implies that the energy of the supernova was 8 x 10(exp 51) ergs, if the Vela remnant is 500 pc away. We can bring this value much closer to typical supernova energies E less than or approximately = 10(exp 51) ergs if the distance to the remnant is revised downward by at least a factor of 2.

Jenkins, Edward B.↗
NASA NTRS1994

Non-sea-salt sulfate and methanesulfonate at American Samoa

High-volume bulk aerosol samples have been collected at American Samoa (14.25 deg S, 170.58 deg W) on a semicontinuous basis since the system was erected as part of the Sea/Air Exchange Program (SEAREX) in March 1983. In this report we consider those samples collected through May 6, 1992. For most of this period the sample filters were changed once a week. However, during November 1989 and from May 10 to June 10, 1990, in conjunction with the aircraft missions of the NASA Global Backscatter Experiment (GLOBE), the filters were changed daily. All of the samples were analyzed for nonsea-salt (nss) SO4(2-) and NO3(-). Analyses for methanesulfonate (MSA) include all of the 53 daily samples, 22 weekly samples from March 19, 1983, through April 12, 1984, and 96 weekly samples from January 3, 1990, through May 6, 1992. The mean concentrations (in micrograms per cubic meter) were 0.37 for nss SO4(2-), 0.0229 for MSA, 0.114 for NO3(-), and 5.1 for Na(+). Nss SO4(2-) and MSA are strongly linearly correlated in these 171 samples (r(exp 2) = 0.66) and the regression intercept does not differ significantly from zero. The geometric mean (GM) nss SO4(2-)/MSA ratio, 18.1 +/- 0.9 (where +/- indicates the 95% confidence interval of the GM) is about 7% higher than had previously been reported for this station. The ratio exhibits no significant seasonal variation. Although the ratio appeared to be significantly lower in the May - June 1990 daily samples (GM = 15.3 +/- 1.2), a further examination of the results indicated that the variance of the measured ratios from 18.1 (the GM for the whole data set) was attributable almost exclusively to the typical random errors in the analyses as determined from the 1 sigma analytical uncertainties of 5% for MSA and SO4(2-) and 2% for Na(+).

Savoie, Dennis L.↗
NASA NTRS1995

Composition of interstellar clouds in the disk and halo. 3: HD 149881

The spectrum of HD 149881, a halo star 1300 pc above the Galactic plane, has been analyzed, based on high-resolution GHRS data from Hubble Space Telescope (HST) together with 21 cm emission observations and profiles of Na I and Ca II features. The results reveal 11 absorption components, of which nine are produced in H I regions, with log N(H(sup 0) in each region mostly approximately 19.5; one component clearly originates in an H II region. Detailed column densities show that (D(Zn)), the absolute value of the depletion D, for Zn, like that for S, does not much exceed 0.1 dex. With Zn used as a standard of reference, D(Fe) varies from -1.1 to -0.6 dex; (D(Cr)) and (D(Mn)) average less than (D(Fe)) by about 0.1 and 0.2 dex, respectively, with dispersions of about 0.1 dex in this difference. As in Papers I and II, the measured D(Si) is consistent with a 2 to 1 ratio of Fe to Si atoms in grains. The kinetic temperature is these H I regions varies widely among components. Maximum temperatures, found from the widths of 21 cm emission components, range from about 100 to 10,000 K, while actual temperatures, found by comparing the H I widths with the b-values for the ultraviolet features, are about equal or less than 1000 K for six of the H I components. In contrast, toward the halo star HD 93521, temperatures of about 6000 K were found for most of the components. With use of these HD 149881 temperatures, values of n(sub e) were obtained from the ionization equilibrium of Ca(+) and also of Na(0). These values range over an order of magnitude, from about 4.9 x 10(exp -2) to 1.3 x 10(exp -3)/cu cm, systematically smaller (but also less certain) than in HD 93521. For the low values of n(sub e) found in the coldest components, the electrons can be accounted for by ionization of C atoms, if n(sub H) approximately equals 10/cu cm. For the warmest component, an ionization probability of beta(H(sup 0)) approximately equals 3 x 10(exp -15)/s is required, with lower values for other H I components.

Spitzer, Lyman, Jr.↗
NASA NTRS1994

Optical Analysis of an Ultra-High resolution Two-Mirror Soft X-Ray Microscope

This work has summarized for a Schwarzschild microscope some relationships between numerical aperture (NA), magnification, diameter of the primary mirror, radius of curvature of the secondary mirror, and the total length of the microscope. To achieve resolutions better than a spherical Schwarzschild microscope of 3.3 Lambda for a perfectly aligned and fabricated system. it is necessary to use aspherical surfaces to control higher-order aberrations. For an NA of 0.35, the aspherical Head microscope provides diffraction limited resolution of 1.4 Lambda where the aspherical surfaces differ from the best fit spherical surface by approximately 1 micrometer. However, the angle of incidence varies significantly over the primary and the secondary mirrors, which will require graded multilayer coatings to operate near peak reflectivities. For higher numerical apertures, the variation of the angle of incidence over the secondary mirror surface becomes a serious problem which must be solved before multilayer coatings can be used for this application. Tolerance analysis of the spherical Schwarzschild microscope has shown that water window operations will require 2-3 times tighter tolerances to achieve a similar performance for operations with 130 A radiation. Surface contour errors have been shown to have a significant impact on the MTF and must be controlled to a peak-to-valley variation of 50-100 A and a frequency of 8 periods over the surface of a mirror.

Shealy, David L.↗
NASA NTRS1997

Studies for the Loss of Atomic and Molecular Species from Io

The general objective of this project is to advance our theoretical understanding of Io's atmosphere by studying how various atomic and molecular species are lost from this atmosphere and are distributed near the satellite and in the circumplanetary environment of Jupiter. The project is divided into well-defined studies described for the likely dominant atmospheric gases involving species of the SO2 family (SO2, SO, 02, 0, S) and for the trace atmospheric gas atomic sodium. The relative abundance of the members of the S02 family and Na (and its parent Na(x)) at the satellite exobase and their relative spatial densities beyond in the extended corona of lo are not well known but will depend upon a number of factors including the upward transport rate of gases from below, the velocity distribution and corresponding escape rate of gases at the exobase, and the operative magnetospheric/solar-photon driven chemistry for the different gases. This question of relative abundance will be studied in this project.

Smyth, William H.↗