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At least 1,747 records · Page 97
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NASA NTRS1973

The auroral green line in Perseid spectra near sunspot maximum

Thirty-one spectra photographed during the Perseid showers of 1969 and 1970 are found to exhibit greater ionization and stronger, more frequent appearance of the forbidden oxygen line at 5577 A than Perseid spectra obtained with the same instrument in 1961. Data from 13 Perseid showers indicate a relationship between the frequency of occurrence of the oxygen line and solar activity. In 1969-70, near sunspot maximum, the strength of this auroral green line is greatest near shower maximum, as though the nature of the meteoroids were a function of their distance from the core of the stream, or, alternatively, the strength of the green line were a function of the altitude of the radiant.

Russell, J. A.↗
NASA NTRS1974

On-line diagnosis of sequential systems, 2

The theory and techniques applicable to the on-line diagnosis of sequential systems, were investigated. A complete model for the study of on-line diagnosis is developed. First an appropriate class of system models is formulated which can serve as a basis for a theoretical study of on-line diagnosis. Then notions of realization, fault, fault-tolerance and diagnosability are formalized which have meaningful interpretations in the the context of on-line diagnosis. The diagnosis of systems which are structurally decomposed and are represented as a network of smaller systems is studied. The fault set considered is the set of faults which only affect one component system is the network. A characterization of those networks which can be diagnosed using a purely combinational detector is achieved. A technique is given which can be used to realize any network by a network which is diagnosable in the above sense. Limits are found on the amount of redundancy involved in any such technique.

Sundstrom, R. J.↗
NASA NTRS1974

Relative coronal abundances derived from X-ray observations 3: The effect of cascades on the relative intensity of Fe (XVII) line fluxes, and a revised iron abundance

Permitted lines in the optically thin coronal X-ray spectrum were analyzed to find the distribution of coronal material, as a function of temperature, without special assumptions concerning coronal conditions. The resonance lines of N, O, Ne, Na, Mg, Al, Si, S, and Ar which dominate the quiet coronal spectrum below 25A were observed. Coronal models were constructed and the relative abundances of these elements were determined. The intensity in the lines of the 2p-3d transitions near 15A was used in conjunction with these coronal models, with the assumption of coronal excitation, to determine the Fe XVII abundance. The relative intensities of the 2p-3d Fe XVII lines observed in the corona agreed with theoretical prediction. Using a more complete theoretical model, and higher resolution observations, a revised calculation of iron abundance relative to hydrogen of 0.000026 was made.

Walker, A. B. C., Jr.↗
NASA NTRS1973

The possible presence of C2 lines in sunspot spectra

Indirect evidence against the presence of C2 lines in umbral spectra is discussed. The dominant role of CO in the molecular equilibrium of C at umbral temperatures ensures that CN, CH and C2 lines are formed in the same atmospheric regions. Observations of CN and CH umbral lines are in good accord with predictions based on accepted umbral model atmospheres. This implies that C2 must follow the predictions and that it is too weak to contribute to the umbral spectrum. C2 lines in the photosphere and penumbrae are in excellent quantitative agreement with predictions. Additional tests are proposed.

Lambert, D. L.↗
NASA NTRS1974

Non-LTE profiles of the Al I autoionization lines

A non-LTE formulation is given for the transfer of radiation in the autoionizing lines of neutral aluminum at 1932 and 1936 A through both the Bilderberg and Harvard-Smithsonian model atmospheres. Numerical solutions for the common source function of these lines and their theoretical line profiles are calculated and compared with the corresponding LTE profiles. The results show that the non-LTE profiles provide a better match with the observations. They also indicate that the continuous opacity of the standard solar models should be increased in this wavelength region if the center-limb variations of observed and theoretical profiles of these lines are to be in reasonable agreement.

Finn, G. D.↗
NASA NTRS1974

Interferometric scans of interstellar K I lines

Results of interferometric scans of the interstellar 7669 wavelength line of neutral potassium are reported toward 26 stars at 1.2 km/sec resolution. The advantages of the K I line, as compared with other optical interstellar lines, are discussed. Recent progress in photoanalytical techniques are shown to make possible the effective realization in practice of the inherent advantages of the K I line.

Hobbs, L. M.↗
NASA NTRS1974

Hook-method measurements of gf-values for ultraviolet Fe I and Fe II lines on a shock tube

Transition probabilities for 14 lines of Fe II and 12 lines of Fe I in the wavelength region 2560-2737 A were measured by use of a shock tube and the hook method. Absolute oscillator strengths for resonance lines of Fe I reported by Banfield and Huber were used to determine the number density of neutral iron in the shock-heated gas. With the assumption of thermal equilibrium, the density of singly ionized iron atoms in this gas was then computed from the measured temperature and pressure with the aid of the Saha equation. Our results on the 12 strongest of the 13 lines belonging to the first ultraviolet multiplet of Fe II indicate that the multiplet f-value is larger by a factor of 2 than that derived from lifetime measurements by Assousa and Smith.

Huber, M. C. E.↗
NASA NTRS1974

Application of infrared line models in the detection of atmospheric pollutants

The total absorptions of the three line profiles, Lorentz, Doppler, and Voight, are compared for a range of intervening parameters. It is found that, for the intermediate path lengths, the use of the combined Lorentz-Doppler (Voight) line profile is essential in calculating the atmospheric transmittance. The line-by-line model transmittance expression is incorporated in the atmospheric radiative flux equation. This equation, in turn, is utilized to determine the pollutant concentration in the atmosphere from the data obtained by the radiation measurement from an aircraft- or satellite-mounted instrument.

Tiwari, S. N.↗
NASA NTRS1974

The broadening of He I lines including ion dynamic corrections, with application to 4471 A

A theory of the broadening of He I lines with forbidden components is developed. The theory takes into account the effects of dynamic ion broadening and is valid at low densities where the forbidden line is reasonably well isolated. Good agreement with experiment and with calculations by Lee (1972) was obtained when the theory was applied at a wavelength of 4471 A. Tables of these data are given and are extended into the line wings beyond the extent of previous tabulations. Reasons for agreement with Lee data are discussed in detail. The density level above which the static ion theory is adequate is defined. A simple numerical profile of allowed lines is also obtained, taking into account dynamic ion effects.

Barnard, A. J.↗
NASA NTRS1975

Solar gamma-ray lines as probes of accelerated particle directionalities in flares

Anisotropies of charged particles accelerated in solar flares were studied by observing Doppler shifts of selected gamma-ray lines. The spectral shape was calculated of the 6.1-MeV line of O-16. If the accelerated particles are isotropic, the line remains centered at e sub 0 = 6129.4 keV, and its width (FWHM) is about 100 keV. For particle anisotropies that may be produced in solar flares, the line is shifted to lower energies by about 30 to 40 keV.

Ramaty, R.↗
NASA NTRS1974

An empirical line-blanketing study of Am stars

Metallic line-blanketing coefficients have been measured over the wavelength range from 3800 to 4700 A in a sample of 20 Am and normal A stars. An expression for the logarithmic iron abundance has been calibrated in terms of effective temperature and a mean line-blocking coefficient. This makes it possible to determine the atmospheric iron abundance in sharp-lined Am and A stars with an accuracy of better than plus or minus 0.1 dex, using only line-blocking measurements and a photometric effective temperature.

Rydgren, A. E.↗
NASA NTRS1975

The interstellar medium near the sun - The line of sight to lambda Scorpii

Copernicus satellite spectrometric observations are used to determine column densities and ionization structure in the local interstellar medium in the line of sight to lambda Sco. Three, or possibly four, regions are identified by physical properties or velocity separations in the UV absorption line profiles, including a region with a temperature near 200,000 K containing O VI lines, one or two H II regions, and an H I region which may also contain S III and C III. Element abundances are tabulated, and abundances in the H I region are shown to have a depletion pattern similar to that for the line of sight to zeta Oph.

York, D. G.↗
NASA NTRS1975

Optically thick line widths in pyrotechnic flares

Experimentally determined sodium line widths for pyrotechnic flares are compared with simple analytical, optically-thick-line-shape calculations. Three ambient pressure levels are considered (760, 150 and 30 torr) for three different flare compositions. The measured line widths range from 1.3 to 481 A. The analytic procedure emphasizes the Lorentz line shape as observed under optically-thick conditions. Calculated widths are in good agreement with the measured values over the entire range.

Douda, B. E.↗
NASA NTRS1974

Experimental liquid line of descent and liquid immiscibility for basalt 70017

The paper describes one possible liquid line of descent produced for a high-titanium mare basalt composition through an arbitrarily chosen series of partial equilibrium and fractional crystallization experiments on basalt 70017. The liquid line of descent leading to immiscibility at 994 C is characterized by enrichment of FeO, K2O, SiO2, and MnO and depletion of MgO and TiO2 in the residual liquids. The composition of the residual liquid at the onset of immiscibility is ferrobasaltic, and the initial appearance of immiscible liquids in the form of silica-rich spherules is in the vicinity of plagioclase-liquid contacts. The integrated bulk composition of the areas of finely exsolved liquids indicates that the trend of the liquid line of descent is at a small angle to the tie lines joining the two liquids.

Rutherford, M. J.↗
NASA NTRS1975

Further observations of the lambda 10830 He line in stars and their significance as a measure of stellar activity

Measurements of the lambda 1030 He line in 198 stars are given along with data on other features in that spectral range. Nearly 80% of all G and K stars show some lambda 10830; of these, half are variable and 1/4 show emission. It was confirmed that lambda 10830 is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars, along with P gamma, but P gamma is not in emission in G and K stars with lambda 10830 emissions. Variable He emission and Ti I emission are found in the RV Tauri variables R Scuti and U Mon. In R Aqr the Fe XIII coronal line lambda 10747 and a line at lambda 11012 which may be singlet He or La II are found, as well as lambda 10830 and P gamma. The nature of coronas or hot chromospheres in the various stars is discussed. It was concluded that the lambda 10830 intensity must be more or less proportional to the energy deposited in the chromosphere corona by non-thermal processes.

Zirin, H.↗
NASA NTRS1976

Gamma ray lines from interstellar grains

The existence of very narrow (FWHM or approximately = 5 KeV) gamma ray line emission from interstellar grains is pointed out. The prime candidate for detection is the line at 6.129 Mev from O-16, but other very narrow lines could also be detected at 0.847, 1.369, 1.634, 1.779 and 2.313 Mev from Fe-56, Mg-24, Ne-20, Si-28 and N-14. Measurements of this line emission can provide information on the composition, size and spatial distribution of interstellar grains.

Lingenfelter, R. E.↗
NASA NTRS1975

Detection of the O III 88.16-micron forbidden line in M17

This paper reports the detection of the fine-structure forbidden line of O III at 88.16 microns in emission from M 17 (the Omega Nebula), which is an optically bright galactic H II region and a strong thermal radio source. The observations were made using an airborne 30-cm telescope and a liquid helium-cooled grating spectrometer with Ge:Ga photoconductive detectors. The line intensity is found to be 2.2 (+1.0, -0.7) by 10 to the -15th power W/sq cm. The results are compared with those of a search for the present line in M 42 as well as with theoretical predictions of the line intensity.

Ward, D. B.↗
NASA NTRS1975

Empirical evidence concerning absorption lines and radiation pressure in quasi-stellar objects

Empirical spectroscopic evidence is examined for the hypothesis that radiation pressure having large gradients with wavelength plays a crucial role in maintaining patterns of redshift differences in quasars. Seventy-four absorption-line redshift systems in 32 quasars and two Seyfert galaxies are analyzed and discussed in terms of the radiation-pressure line-locking hypothesis. Redshift line ratios greater than unity are computed for each quasar and plotted as histograms. Ratios which may indicate line and edge locking are identified, including those of the C IV and Mg II doublets and those of the N III/C III, He II/O III, C II/He I, Ly-beta/H I, and H I/He I ionization edges.

Burbidge, E. M.↗