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At least 415 records · Page 23
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NASA NTRS1973

Theory of interstellar abundances of the isotopes of carbon, nitrogen and oxygen.

It is shown that CNO hydrogen burning in stars with a mass of 3 to 8 solar masses can account for both the likely abundances of C-13, N-14, and O-17 in the interstellar medium and the observed ratios C-12/C-13 O-16/O-17 in the atmospheres of evolved stars. A model which gives these abundances is shown to be consistent also with previously suggested mechanisms for the production of He-3, N-15, and O-18.

Wollman, E. R.↗
NASA NTRS1973

A mechanism for the abundance enhancements of heavy nuclei in solar flare particle events

A mechanism is proposed to account for the recently reported abundance enhancements of heavy nuclei in solar flares. The mechanism requires two acceleration stages for its operation: First, fully stripped ions are accelerated to suprathermal energies, and subsequently, a fraction of these ions are Fermi accelerated to higher energies. It is shown that because injection into Fermi acceleration is rigidity dependent and the ions may pick up electrons during transport to the Fermi acceleration region, an enhancement of the abundances of heavy nuclei can occur. The degree of the enhancement depends on a number of factors particular to each flare, so that the degree of enhancement may be variable from flare to flare, or may be a function of time within a given flare. In some flares, conditions may be such that no enhancement would be expected.

Cartwright, B. G.↗
NASA NTRS1973

Abundances in the Crab Nebula

The bright visual-wavelength emission lines in spectra of filaments in the Crab Nebula cannot be used to derive unique values for the relative abundances of elements there, even under a simplifying assumption that heating is due entirely to photoionization by the Crab's nonthermal continuum. However, a range of possibilities may be estimated. By mass, helium is more abundant than hydrogen; but the mass fraction of heavier elements may be surprisingly small. Such conclusions are subject to modification if a noticeable fraction of the energy density involves fast particles around 1 MeV.

Davidson, K.↗
NASA NTRS1973

Iron abundance in the moon from magnetometer measurements

Apollo 12 and 15 lunar surface magnetometer data with simultaneous lunar orbiting Explorer 35 data are used to plot hysteresis curves for the whole moon. From these curves a whole-moon permeability of 1.029 (+0.024 or -0.019) is calculated. This result implies that the moon is not composed entirely of paramagnetic material, but that ferromagnetic material such as free iron exists in sufficient amounts to dominate the bulk lunar susceptibility. From the magnetic data the ferromagnetic free iron abundance is calculated. Then for assumed compositional models of the moon the additional paramagnetic iron is determined, yielding total lunar iron content. The calculated abundances are as follows: ferromagnetic free iron, 5 plus or minus 4 wt %; total iron in the moon, 9 plus or minus 4 wt %.

Parkin, C. W.↗
NASA NTRS1974

Abundances relative to carbon of the elements silicon to nickel in the galactic cosmic radiation

Discussion of the abundances relative to carbon of the elements from silicon to nickel in the galactic cosmic radiation as measured by cosmic ray telescopes on the IMP-5 and IMP-7 satellites, in energy ranges between 40 and 450 MeV/nucleon depending on the species. The IMP-7 measurements are still to be considered only preliminary and do not yet fully exploit the resolution capabilities of that instrument. Calculations of the abundances to be expected in this charge range if the cosmic radiation traverses 6 g/sq cm of material after acceleration are presented, and the consequences which follow both for propagation models and for the chemical composition of the sources of the cosmic radiation are discussed.

Cartwright, B.↗
NASA NTRS1974

Measurement of elemental abundance of very low energy solar cosmic rays

Heavy interplanetary particles (Z from 3 to 30) have been observed during a solar flare period between October 29 and November 4, 1972. The nuclear abundance has been determined by a two parameter analysis of a thin window proportional counter - solid state detector device aboard the Explorer 47 (IMP-7) satellite. Energy spectra are given for C, O and Fe. The elemental abundance relative to oxygen is determined for carbon, neon, magnesium, silicon and the iron group in the energy range 0.62 to 6.9 MeV/nucleon. For the Fe/O ratio no energy dependence could be observed within the error limits.

Hovestadt, D.↗
NASA NTRS1974

The solar abundance of beryllium

The solar abundance of beryllium is deduced from high-resolution Kitt Peak observations of the 3130.43- and 3131.08-A lines of Be II interpreted by the method of spectrum synthesis. The results are in good agreement with those previously obtained by Grevesse (1968) and by Hauge and Engvold (1968) and indicate that in the photospheric layers, beryllium is depleted below the chondritic value by a factor of about two. It is found that the beryllium abundance is equal to logN(Be)/N(H) + 12 = 1.08 plus or minus 0.05.

Ross, J. E.↗
NASA NTRS1974

The abundances of nuclei in the cosmic radiation

The relative abundances are treated as a consequence of processes in cosmic ray transport occurring during passage of the radiation through interstellar material at high velocity. Some of the subjects mentioned are nuclear fragmentation and the production of secondary nuclei, nuclear reactions, energy loss and nuclear decay, ionization, the range-energy relation and propagation variables, capture and loss of electrons, the propagation of nuclei, the transport equation, equilibrium solutions, energy-dependent path length distribution, exponential path length distributions, discrete spectra, sources, supernovae, and the origin of the abundances. The connection between the space-time features of the sources, the material traversed, and the effects of magnetic fields is established by describing the particle-field interaction as a diffusive or random-walk process.

Reames, D. V.↗
NASA NTRS1974

Solar particle events with anomalously large relative abundance of He-3

Experimental results are reported on three energetic particle events with extremely high abundance of He-3. The measurements were taken onboard the OGO-5 satellite. It was shown that the abundance of protons relative to He nuclei were significantly low in these events. Not more than four H-2 and three H-3 were detected during the entire period under study compared to 1110 H-3 nuclei. The limitations these observations place on theoretical models are discussed to explain He-3 flares.

Serlemitsos, A. T.↗
NASA NTRS1974

Elemental abundances in interplanetary dust

The paper reports on measurements taken of elemental abundances in two interplanetary dust grains. Meteoroidal residue found inside micrometeoritic craters was discovered by optically scanning the 800 sq cm aluminum surface of the S-228 transuranic cosmic-ray experiment exposed to space for 67d during the Skylab-IV mission. Crater analyses for two randomly sampled meteoroids showed a composition consistent with troilite in the 9 micron-minute particle. Chondritic abundances were found in the 30 micron-minute particle. Particles of similar size and chemistry were common in carbonaceous chondrite meteorites. The inferred grain sizes within the 30 micron-minute particle provided evidence for the similarity to carbonaceous chondrites rather than to other meteorite types.

Brownlee, D. E.↗
NASA NTRS1975

Oxygen-to-neon abundance ratio in the solar corona

The oxygen-to-neon abundance ratio in the solar corona is determined to be 4.7 + or - 1.5 on the basis of a relatively model-independent analysis utilizing 25 separate measurements of the O VIII to Ne IX resonance line ratio. The stated uncertainty includes random and possible systematic experimental error in the data but does not include possible error in the calculated flux ratios which have been fitted to the observations. This abundance ratio is smaller than most published results based upon EUV or X-ray observations but is in good agreement with direct measurements of flare cosmic rays.

Acton, L. W.↗
NASA NTRS1975

Isotopic abundance ratios for carbon and nitrogen in Nova Herculis 1934

Spectra of Nova Herculis 1934 taken during an episode of intense CN absorption are analyzed to determine the isotopic abundance ratios of C12/C13 and N14/N15. Synthetic spectrum analysis, based on the wavelengths, excitation potentials, and oscillator strengths for the CN lines, and radial velocity measurements indicate that C(12)N(14) was the dominant species in the Nova, and that the minimum abundance limit for C12/C13 is about 1.5, while the minimum for N14/N15 is about 2. The results are compared with predictions based on models of thermonuclear runaways in hydrogen-rich envelopes of white dwarfs. It is noted that the nova material may have been contaminated with C13-rich material prior to or during the eruption. Possible causes of this isotope enrichment are presented.

Sneden, C.↗
NASA NTRS1975

Effects of primordial fluctuations on the abundances of light elements

Some of the effects of primordial inhomogeneities on the production of H-2, He-3, and Li-7 are investigated. For the most part, temperature fluctuations have only small effects on the abundances. The density fluctuations are modeled by a unimodal distribution so that the Universe is characterized by the mean density and the relative amplitude of the density variations. It has been found that the constraint which H-2 production imposes on the mean mass density is eased somewhat by allowing for density inhomogeneities. However, unless the composition of the interstellar matter is atypical of most of the matter in the Universe, the mass density will be at least a factor of 3 below the critical density. For reasonable estimates of the pregalactic abundances, sufficient He-3 and Li-7 cannot be produced in the same model universe. Production of both Li-7 and H-2 requires large-amplitude primordial fluctuations, while sufficient He-3 and H-2 can be formed in very low-density, fairly homogeneous universes.

Epstein, R. I.↗
NASA NTRS1975

Solar particle events with anomalously large relative abundance of He-3

Energetic particle data are presented from a series of solar flares with a relative abundance of He-3 much higher than that of any previous events. The abundance of protons relative to He nuclei was significantly low in these events; not more than four H-2 and three H-3 were detected during the entire period under study, compared with 1110 He-3 nuclei. Results from these experiments are compared with data available from other investigations, and the limitations the former observations place on theoretical models to explain He-3-rich flares are discussed.

Serlemitsos, A. T.↗
NASA NTRS1974

Modeling the evolution of Sm and Eu abundances during lunar igneous differentiation

The current work presents models for the evolution of europium and samarium abundances during lunar igneous processes. The effect of probable variations in lunar temperature and oxygen fugacity, mineral-liquid distribution coefficients, and the crystallization or melting progression are considered in the model calculations. Changes in the proportions of crystallizing phases strongly influence the evolution of trace element abundances during fractional crystallization, and models must include realistic estimates of the major phase equilibria during crystallization. The results are applied to evaluating the possibility of generating KREEP-rich materials by lunar igneous processes.

Weill, D. F.↗
NASA NTRS1974

Sulfur abundances and distributions in the valley of Taurus-Littrow

Total sulfur abundances have been determined for 36 Apollo 17 soil, breccia and crystalline rock samples. Sulfur concentrations range from 550 to 1300 micrograms S/g for soil samples, with the orange soil containing the lowest amount of sulfur. Noritic breccias contain between 720 and 950 micrograms S/g, while the anorthositic rocks have sulfur contents of 270 and 368 micrograms S/g. The dunite 72415 contained the lowest sulfur content (44 micrograms S/g) of any Apollo 17 sample studied. Apollo 17 basalts have unusually high sulfur contents (1580-2770 micrograms S/g) as compared to Apollo 12 and 15 basalts and terrestrial basalts. Sulfur abundances for the Apollo 17 basalts are almost identical to those from Apollo 11 basalts. A negative correlation between percent metallic iron and total sulfur for the Apollo 17 and 15 basalts was found and suggests that a portion of the metallic iron in lunar basalts may result from desulfuration of the melt prior to crystallization from the lunar magma.

Gibson, E. K., Jr.↗
NASA NTRS1975

Semiperiodic variations in CO2 abundance on Venus

Tests of the uniqueness of periodicity in the strength of the P branch (P2-P38) of the 8689 A CO2 band on Venus are described. It was found that the observed 4-day periodicity was not unique. The periodicity indicated an increasing asymmetry between the northern and southern hemispheres with approach to inferior conjunction or with increasing phase angle. When the slit positions of the various scans were referred to the planet or atmospheric equator rather than to the intensity equator, at inferior conjunction, the slit positions having a factor of two greater CO2 abundance or line strength were over the polar latitudes of the atmosphere. Similarly, the lower-abundance slit positions were over the equatorial latitudes of the atmosphere. It is thus concluded that the level of line formation must be lower over polar latitudes than over equatorial regions.

Barker, E. S.↗
NASA NTRS1975

Metal abundances of RR Lyrae stars in galactic globular clusters

Results are reported for image-tube scanner measurements of Preston's (1959) metal-abundance indicator and metallic-line absorption in the G-band region (4285 to 4317 A) of 47 RR Lyrae stars in 12 galactic globular clusters and 67 RR Lyrae field stars. The relationship (Fe/H) is defined and determined from curve-of-growth analyses of 13 RR Lyrae field stars, while a comparison of metal-abundance vs metallic-line absorption relationships derived for the field and cluster stars indicates that both groups can be calibrated in the same way. Based on this calibration, (Fe/H) values are deduced for the globular-cluster stars and the clusters themselves. It is found that the alpha-rich phenomenon is present in these stars and is confined to calcium and titanium.

Butler, D.↗