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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Interstellar Abundances Toward X Per, Revisited

The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to measure elemental abundances in the local ISM. We examine absorption features of 0, Mg, and Si along this line of sight using spectra from the Chandra Observatory's LETG/ ACIS-S and XMM-Newton's RGS instruments. In general, we find that the abundances and their ratios are similar to those of young F and G stars and the most recent solar values. We compare our results with abundances required by dust grain models.

XPer↗
NASA NTRS2014

THE SuperTIGER Instrument: Measurement of Elemental Abundances of Ultra-Heavy Galactic Cosmic Rays

The SuperTIGER (Super Trans-Iron Galactic Element Recorder) instrument was developed to measure the abundances of galactic cosmic-ray elements from Ne-10 to Zr-40 with individual element resolution and the high statistics needed to test models of cosmic-ray origins. SuperTIGER also makes exploratory measurements of the abundances of elements with 40 < Z < or = 60 and measures the energy spectra of the more abundant elements for Z < or = 30 from about 0.8 to 10 GeV/nucleon. This instrument is an enlarged and higher resolution version of the earlier TIGER instrument. It was designed to provide the largest geometric acceptance possible and to reach as high an altitude as possible, flying on a standard long-duration 1.11 million cu m balloon. SuperTIGER was launched from Williams Field, McMurdo Station, Antarctica, on 2012 December 8, and made about 2.7 revolutions around the South Pole in 55 days of flight, returning data on over 50 x 10(exp 6) cosmic-ray nuclei with Z > or = 10, including approx.1300 with Z > 29 and approx.60 with Z > 49. Here, we describe the instrument, the methods of charge identification employed, the SuperTIGER balloon flight, and the instrument performance.

abundances↗
NASA NTRS1972

Velocity and flux dependence of the solar-wind helium abundance.

The causes of the variations in the relative abundance of helium in the solar wind are not understood. To define the theoretical problem more precisely, empirical relationships between helium abundances and other pertinent solar-wind parameters are necessary. In this report we show that the average percentage of helium increases with the solar-wind velocity. We also confirm that the abundance of helium tends to be higher for low solar-wind fluxes rather than lower as expected from theory. The interpretation of these results is discussed, and it is concluded that more realistic theoretical treatments of the problem are necessary before these results can be understood in terms of models of the solar corona and solar wind.

Hirshberg, J.↗
NASA NTRS1974

Iron abundance and magnetic permeability of the moon

A set of simultaneous data from the Apollo 12 lunar surface magnetometer and the Explorer 35 Ames magnetometer are used to construct a whole-moon hysteresis curve, from which a new value of global lunar permeability is determined to be mu = 1.012 + or - 0.006. The corresponding global induced dipole moment is 2.1 x 10 to the 18th power gauss-cucm for typical inducing fields of .1000 gauss in the lunar environment. From the permeability measurement, lunar free iron abundance is determined to be 2.5 + or - 2.0 wt. %. Total iron abundance is calculated for two assumed compositional models of the lunar interior: a free iron/orthopyroxene lunar composition and a free iron/olivine composition. The overall lunar total iron abundance is determined to be 9.0 + or - 4.7 wt. %. Other lunar models with a small iron core and with a shallow iron-rich layer are discussed in light of the measured global permeability. Effects on permeability and iron content calculations due to a possible lunar ionosphere are also considered.

Parkin, C. W.↗
NASA NTRS1974

Iron abundance and magnetic permeability of the moon

A larger set of simultaneous data from the Apollo 12 lunar surface magnetometer and the Explorer 35 Ames magnetometer are used to construct a whole-moon hysteresis curve, from which a new value of global lunar permeability is determined to be mu = 1.012 + or - 0.006. The corresponding global induced dipole moment is 2.1 x 10 to the 18th power gauss-cu cm for typical inducing fields of .0001 gauss in the lunar environment. From the permeability measurement, lunar free iron abundance is determined to be 2.5 + or - 2.0 wt. %. Total iron abundance (sum of iron in the ferromagnetic and paramagnetic states) is calculated for two assumed compositional models of the lunar interior: a free iron/orthopyroxene lunar composition and a free iron/olivine composition. The overall lunar total iron abundance is determined to be 9.0 + or - 4.7 wt. %. Other lunar models with a small iron core and with a shallow iron-rich layer are discussed in light of the measured global permeability.

Parkin, C. W.↗
NASA NTRS1974

The solar cycle variation of the solar wind helium abundance

A critical survey was made of the experimental evidence for a variation of the relative abundance by number h, (n alpha/np), of helium in the solar wind. The abundance is found to vary by delta h = 0.01 + or - 0.01 from 0.035 to 0.045 over solar cycle 20. Changes in the average bulk speed during the solar activity cycle was insufficient to account for this increase in h with the solar cycle. The slope of the linear relation between h and the plasma bulk speed is also found to vary, being greatest around solar maximum. An attempt is made to explain the 30% variation in h as the result of the variation in the number of major solar flares over a solar cycle. These obvious transients are apparently not numerous enough to explain the observed variation, but the reasonable expectation remains that the transients observed recently by Skylab which may occur more frequently than major flares could augment those associated with major flares. Since the solar wind flux is not observed to increase at solar maximum, the abundance of Helium cannot be proportional to the proton flux leaving the sun unless the solar wind comes from a smaller area of the sun at maximum than at minimum.

Ogilvie, K. W.↗
NASA NTRS1973

Carbon and sulfur distributions and abundances in lunar fines

Total sulfur abundances have been determined for 20 Apollo 14, 15, and 16 soil samples and one Apollo 14 breccia. Sulfur concentrations range from 474 to 844 microg S/g. Volatilization experiments on selected samples have been carried out using step-wise heating. Sample residues have been analyzed for their total carbon and sulfur abundances to establish the material balance in lunar fines for these two elements. Volatilization experiments have established that between 31 to 54 microg C/g remains in soils which have been heated at 1100 C for 24 hours under vacuum. The residual carbon is believed to be indigenous lunar carbon whereas all forms of carbon lost from samples below 1100 C is extralunar carbon. Total carbon and sulfur abundances taken from the literature have been used to show the depletion of volatile elements with increasing grade for the Apollo 14 breccias.

Gibson, E. K., Jr.↗
NASA NTRS1974

Interstellar abundances - Gas and dust

Data on abundances of interstellar atoms, ions and molecules in front of zeta Oph are assembled and analyzed. The gas-phase abundances of at least 11 heavy elements are significantly lower, relative to hydrogen, than in the solar system. The abundance deficiencies of certain elements correlate with the temperatures derived theoretically for particle condensation in stellar atmospheres or nebulae, suggesting that these elements have condensed into dust grains near stars. There is evidence that other elements have accreted onto such grains after their arrival in interstellar space. The extinction spectrum of zeta Oph can be explained qualitatively and, to a degree, quantitatively by dust grains composed of silicates, graphite, silicon carbide, and iron, with mantles composed of complex molecules of H, C, N, and O. This composition is consistent with the observed gas-phase deficiencies.

Field, G. B.↗
NASA NTRS1974

On the abundance of Europium

The inclusion of the effects of hyperfine splitting can significantly lower the abundance estimate of Eu from singly ionized lines which lie on the flat portion of the curve of growth. In the 21 cool Ap stars studied by Adelman and the five Am stars studied by Smith, the Eu abundance was reduced by 0.4 dex on the average. In individual cases, the reductions were as great as 0.9 dex. This makes the Eu abundance comparable to that of its neighboring rare earths Sm and Gd in the Ap stars and less than Sm and Gd in the Am stars, but still substantially overabundant with respect to solar values.

Hartoog, M. R.↗
NASA NTRS1974

The abundance of ammonia on Jupiter, Saturn and Titan

From recent spectra of Jupiter, Saturn and Titan in the 6450-A band of NH3, new values of the abundance of ammonia are derived for Jupiter and Saturn. NH3 abundances of 13 plus or minus 3 m-Am on Jupiter and 2 plus or minus 1 m-Am on Saturn were found. High resolution profiles of NH3 lines on Jupiter are used to estimate a pressure of 2.1 atm at the line formation level in the Jovian atmosphere. In the case of Titan, an NH3 abundance of less than 2 m-Am was found. The implications of these results are discussed.

Encrenaz, T.↗
NASA NTRS1974

Abundances of the group IVB elements, Ti, Zr, and Hf and implications of their ratios in lunar materials

New data on Zr and Hf abundances in samples from recent Apollo missions and a few from earlier missions are presented. The data confirm our previous suggestion of a modest Zr-Hf fractionation among lunar rock types. The four major lunar rock types can be readily distinguished, based on Zr and Hf abundances and Zr/Hf mass ratios. Mare basalts exhibit mean Zr abundances ranging from 111 ppm for Apollo 15 to 534 ppm for Apollo 11 and low Zr/Hf mass ratios ranging from 34 to 39. KREEP basalts are characterized by very high Zr contents (mean = 1380 ppm Zr) and high Zr/Hf ratio of 47. Anorthosites exhibit extremely low Zr and Hf contents and possibly very low Zr/Hf ratios. Arguments that the fractionation may be partly due to the presence of Zr(3+) in lunar magmas while Hf remains as Hf(4+) are presented. These data for Zr and Hf together with data for Ti recently obtained on the same samples in our laboratory are discussed in support of a modified two-stage lunar crustal evolution model.

Ehmann, W. D.↗
NASA NTRS1974

Iron abundance and magnetic permeability of the moon

A larger set of simultaneous data from the Apollo 12 lunar surface magnetometer and the Explorer 35 Ames magnetometer are used to construct a whole-moon hysteresis curve, from which a new value of global lunar permeability is determined to be mu = 1.012 + or - 0.006. The corresponding global induced dipole moment is 2.1 times ten to the eighteenth power gauss-cu cm for typical inducing fields of one ten-thousandth gauss in the lunar environment. From the permeability measurement, lunar free iron abundance is determined to be 2.5 + or - 2.0 wt %. Total iron abundance (sum of iron in the ferromagnetic and paramagnetic states) is calculated for two assumed compositional models of the lunar interior: a free iron/orthopyroxene lunar composition and a free iron/olivine composition. The overall lunar total iron abundance is determined to be 9.0 + or - 4.7 wt %. Other lunar models with a small iron core and with a shallow iron-rich layer are discussed in light of the measured global permeability. Effects on permeability and iron content calculations due to a possible lunar ionosphere are also considered.

Parkin, C. W.↗
NASA NTRS1975

The solar flare iron line to continuum ratio and the coronal abundances of iron and helium

Narrow band Ross filter measurements of the Fe 25 line flux around 0.185 nm and simultaneous broadband measurements during a solar flare were used to determine the relationship between the solar coronal abundances of iron and helium. The Fe 25 ion population was also determined as a function of time. The proportional counter and the Ross filter on OSO-7 were utilized. The data were analyzed under the separate assumptions that (1) the electron density was high enough that a single temperature could characterize the continuum spectrum and the ionization equilibrium, and that (2) the electron density was low so that the ion populations trailed the electron temperature in time. It was found that the density was at least 5x10 to the 9th power, and that the high density assumption was valid. It was also found that the iron abundance is 0.000011 for a helium abundance of 0.2, relative to hydrogen.

Mckenzie, D. L.↗
NASA NTRS1975

A measurement of abundances of VVH nuclei above 0.6 GeV per nucleon

The abundance distribution of very very heavy (VVH) nuclei just beyond the iron group has been measured with a balloon-borne counter telescope flown in 1971 and 1972. While the statistical accuracy of these observations is limited, they are of considerable interest since very little work has so far been done to determine the abundance of nuclei with charge between 27 and 36. It is found that the element distribution in the cosmic rays arriving at the top of the atmosphere is quite similar to the solar-system abundance distribution in this interval.

Juliusson, E.↗
NASA NTRS1975

A new solar carbon abundance based on non-LTE CN molecular spectra

A detailed non-LTE analysis of solar CN spectra strongly suggest a revised carbon abundance for the sun. We recommend a value of log carbon abundance = 8.35 plus or minus 0.15 which is significantly lower than the presently accepted value of log carbon abundance = 8.55. This revision may have important consequences in astrophysics.

Mount, G. H.↗
NASA NTRS1975

Uranian methane abundance, rotational temperature, and effective pressure from the 6800 A band

Measurements of the methane absorption features at 6800 A in two spectrograms of Uranus have been analyzed on the working hypothesis that the features are the R branch of the 5 mu(3) rotation-vibration overtone. Internal and external consistencies in temperature calculations from the measurements give increased confidence that the band identification and rotational-quantum-number assignments to band members are correct. Parametric fitting of synthetic reflecting-layer and homogeneous scattering-layer spectra to the spectrograms is attempted. The best-fit methane abundances, taken with recent estimates of the molecular hydrogen abundance, correspond to an average C:H ratio between 1.5 and 25 times larger than the solar ratio. Even greater enrichment of the C:H ratio may occur below the visible cloud boundary. High spectroscopic resolution of the present data permits direct measurement of the methane line halfwidth in Uranus's spectrum. The halfwidth corresponds to an effective pressure greater than 3 atm, depending on the mixture of atmospheric gases. Pressure in this range, at the methane rotational temperature of between 93 and 100 K, is inconsistent with current Uranus atmosphere models having solar elemental-abundance ratios. It is consistent with models which are considerably enriched in 'heavier' constituents.

Bergstralh, J. T.↗
NASA NTRS1975

A balloon measurement of the cosmic ray element abundances

The experiment described was flown from Thompson, Canada in August, 1973 to measure the cosmic ray element abundances in the atmosphere. All particles used in the analysis, including approximately 25,000 oxygen and 1600 iron nuclei, had sufficient energy at the top of the atmosphere to trigger the Cerenkov counter. Nuclei between beryllium and nickel were identified, using two plastic scintillators and an acrylic plastic Cerenkov counter. The relative composition and fluxes are determined. Agreement with earlier measurements in the atmosphere is within 5%; however, larger differences appear in composition extrapolated to the top of the atmosphere. In particular, the nitrogen abundance is almost 20% higher and the iron abundance is 20% lower than the generally accepted values.

Ormes, J. F.↗
NASA NTRS1976

Evolution of major mineral compositions and trace element abundances during fractional crystallization of a model lunar composition

The evolution of major mineral compositions and trace element abundances during perfect fractional crystallization of a model lunar magma ocean was calculated. The minerals in the model lunar composition were olivine, orthopyroxene, clinopyroxene, and plagioclase. Lunar bulk composition data, major mineral/melt equilibria data, and trace element partition data were taken from published sources. The results show olivine beginning to crystallize at 1380 C. Approximately 50% of the system crystallizes as olivine. From 50 to 60% solidification, orthopyroxene crystallizes alone. During the final 40% solidification, Ca-rich clinopyroxene and plagioclase crystallize together. Various changes in composition of all these minerals are also noted during the process. Concomitant evolution of major element abundances in the melt is followed along with that of trace element abundances. Consequences of the results for constraints on some aspects of the composition of the lunar magma ocean and of the primitive moon are discussed.

Drake, M. J.↗