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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The neutral oxygen spectrum. 2: Pumping by hydrogen Lyman-beta under the optically thin condition: A first application to the classical novae

A calculation, employing a detailed model of neutral oxygen, is carried out to give fluorescent line intensities expected in a long-proposed photoexcitation by accidental resonance (PAR) process in which hydrogen Lyman-beta photoexcites the oxygen spectrum. The results pertain to the optically thin case but provide an upper limit to the fluorescent intensities which can be attained. They are applied to analyze line ratios involving the strong 8446 A line observed in classical novae during the diffusion-enhanced and Orion phases. Operation of the PAR process in the novae is verified. It is found that photoexcitation rates in the ejecta reach values greater than 0.1/sec, corresponding to hydrogen Lyman-beta radiation field intensities greater than 1250 ergs/cm/sec/sr.

Kastner, S. O.↗
NASA NTRS1995

The neutral oxygen spectrum. 1: Collisionally excited level populations and line intensities under optically thin conditions

This is the first paper in a projected program to produce quantitative information on the spectrum of the neutral oxygen atom under a variety of excitation conditions. Radiative rates and effective collision strengths are assembled from the recent literature where available, or are calculated for as yet untreated transitions using the University College superstructure/distorted-wave computer package, to produce a complete set of atomic data for a 13 hybrid level model of neutral oxygen. Level populations and relative intensities for 28 allowed, inter-combination, and forbidden oxygen lines are computed, under optically thin conditions, for the electron density range 4.0 less than log N(sub e) less than 12.0 and the electron temperature values T(sub e) = 5000, 10,000, 20,000, 50,000, and 100,000 K. Preliminary applications to observed intercombination/allowed and forbidden/allowed line ratios are discussed.

Bhatia, A. K.↗
NASA NTRS1986

Changes in the energy spectrum of anomalous oxygen during 1977-1985

Spatial and temporal variations of the interplanetary cosmic ray oxygen spectrum over the 11 yr solar and cosmic ray modulation cycle are discussed. The variations were monitored with instrumentation on the Voyager 1 and 2 and the Pioneer 10 spacecraft over the period 1977-85. The analysis concentrates on 4-30 MeV nuclei, where the anomalous component of cosmic rays dominates. The number of particles of anomalous oxygen increased with increasing distance from the sun. Furthermore, the particles exhibited, on the average, higher energies after the middle of 1980, when a solar magnetic field reversal occurred. The Voyager 1 spacecraft, 24 deg out of the ecliptic plane, did not register as high a shift in energy during the same period. It is concluded that cosmic ray drift effects are closely associated with solar magnetic field polarity reversals, a situation which may be examined more fully during the solar minimum beginning in 1985.

Cummings, A. C.↗
NASA NTRS1971

Influence of the chemical bond on the K emission spectrum of oxygen and fluorine.

The K emission spectrum of oxygen and fluorine from a number of simple oxides and fluorides is divided into three to six sub-peaks. The spectra of many of these oxides and fluorides resemble one another owing to their basically ionic bonding. Certain sub-peaks, however, are ascribed to cross-over transitions and partially covalent energy levels. The different fluorine spectrum of Teflon is due to the hybrid nature of its covalent bonds.

Koster, A. S.↗
NASA NTRS1973

Attenuation and phase dispersion in the atmosphere due to the microwave spectrum of oxygen

Radio wave propagation in the 40- to 140-GHz band through the earth's atmosphere is strongly influenced by the behavior of the O2 microwave spectrum. This behavior causes the transfer function to depend critically upon altitude. The spectroscopic properties of O2 are discussed and reduced to engineering formulas expressing attenuation and phase dispersion rates in terms of frequency and meteorological parameters. The theory is supported on several accounts by reliable spectroscopic measurements. Pressure scanning spectroscopy is used to investigate the O2 microwave spectrum under simulated atmospheric conditions. The application of spectroscopic information to analytical treatments of transfer properties for inhomogeneous slant paths is demonstrated. Attenuation and phase dispersion between 49 and 72 GHz are evaluated for zenith and tangential paths.

Liebe, H. J.↗
NASA NTRS1986

Solar cycle variations of anomalous He-4 as deduced by studies of cosmic ray He-3

Voyager 1 and 2 observations have been used to derive the energy spectrum of 'anomalous' cosmic-ray (ACR) He using a technique based on the separation of the isotopes of He. Previously reported observations show that the ACR oxygen spectrum underwent a change in shape following the solar magnetic field reversal in 1980; in this paper evidence for a corresponding change in the ACR He spectrum is presented. It is found that the energy spectra of ACR He and oxygen and Galactic-cosmic-ray He-4 and He3 can be reproduced both before and after the field reversal using a simple solar modulation model in which the effects of curvature and gradient drifts are arbitrarily neglected.

Cummings, A. C.↗
NASA NTRS1980

A power law fit to oxygen absorption at 60 GHz and its application to remote sensing of atmospheric temperature

The paper presents an empirical study of the oxygen spectrum near 60 GHz with reference to its applicability to the remote sensing of the tropospheric and lower stratospheric temperature. It is demonstrated that the absorption coefficient of oxygen at 60 GHz can be fitted to the power law form with a relative rms error of about 8%. The power law form, when used in conjunction with the weighting function, permits the definition of some basic quantities in the passive remote sensing of the atmospheric temperature. It is shown how the power law form has been utilized in processing data from the Nimbus 5 microwave spectrometer experiment. The algorithm presented can be applied to spectrometer experiments at infrared frequencies.

Poon, R. K. L.↗
NASA NTRS1975

K-alpha X-rays from cosmic ray oxygen

Equilibrium charge fractions are calculated for subrelativistic cosmic ray oxygen ions in the interstellar medium. These are used to determine the expected flux of K-alpha rays arising from atomic processes for a number of different postulated interstellar oxygen spectra. Relating these results to the diffuse X-ray background measured at the appropriate energy level suggests an observable line feature. If the flux of low energy cosmic ray oxygen is sufficiently large, K-alpha X-ray line emission from these nuclei will comprise a significant fraction of the total diffuse flux at approximately 0.6 keV. A satellite borne detector with a resolution greater than 30 percent could observe this feature if the subrelativistic interstellar cosmic ray oxygen spectrum is as large as certain theoretical estimates expressed in the text.

Pravdo, S. H.↗
NASA NTRS1985

Changes in the energy spectrum of anomalous oxygen and helium during 1977-1985

Data was used from the cosmic ray experiment on the Voyager spacecraft to measure the energy spectrum of anomalous O and He during the period 1977 to 1985. These spectra are found to change dramatically after the middle of 1980, with the peak of plateau region of the differential spectrum shifting to a higher energy. This change appears to be related to the reversal of the solar magnetic field and could imply that particle drifts are important to the acceleration of propagation of these particles.

Cummings, A. C.↗
NASA NTRS1985

Changes in the energy spectrum of anomalous oxygen and helium during 1977 - 1985

Data from the cosmic-ray experiment on the Voyager spacecraft was used to assure the energy spectrum of anomalous O and He during the period 1977 to 1985. These spectra change dramatically after the middle of 1980, with the peak or plateau region of the differential spectrum shifting to a higher energy. This change appears to be related to the reversal of the solar magnetic field and could imply that particle drifts are important to the acceleration or propagation of these particles.

Cummings, A. C.↗
NASA NTRS1981

The ultraviolet dayglow. IV - The spectrum and excitation of singly ionized oxygen

The emission line spectrum of singly ionized atomic oxygen (O II) dominates the day airglow spectrum in the extreme ultraviolet below 834 A. The strongest resonance line, at 834 A, is optically thick and an analysis of height profiles obtained from rocket observations between 140 and 265 km in specific viewing directions indicates that the principal excitation source is direct photoionization of neutral atomic oxygen. Strong emission at 538-539 A is most likely due to the quartet rather than the doublet transitions, which both occur at these wavelengths and which are not spectrally resolved in the data. The intensities of the weaker lines are consistent with recent laboratory measurements of transition branching ratios. Several strong O II lines near He I 584 produce severe contamination of low-altitude (less than 400 km) measurements of geocoronal helium emission made with thin-film broadband photometers.

Feldman, P. D.↗