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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The line-locking hypothesis, absorption by intervening galaxies, and the z = 1.95 peak in redshifts

The controversy over whether the absorption spectrum in QSOs is intrinsic or extrinsic is approached with attention to the peak of redshifts at z = 1.95. Also considered are the line-locking and the intervening galaxy hypotheses. The line locking hypothesis is based on observations that certain ratios found in absorption line QSOs are preferred, and leads inevitably to the conclusion that the absorption line systems are intrinsic. The intervening galaxy hypothesis is based on absorption redshifts resulting from given absorption cross-sections of galactic clusters and the intergalactic medium, and would lead to the theoretical conclusion that most QSOs show strong absorption, a conclusion which is not supported by empirical data. The 1.95 peak, on the other hand, is most probably an intrinsic property of QSOs. The peak is enhanced by redshift, and it is noted that both an emission and an absorption redshift peak are seen at 1.95.

Burbidge, G.↗
NASA NTRS1978

Limb-brightening observations from the OSO-7 satellite. III - Comparison of EUV line intensities of Fe XII, Fe XI, Fe XV, Si X and S XII, Si IX and S XI with predictions

Continuing a study of heliocentric dependence of EUV emission line intensities observed by the Goddard OSO-7 spectroheliograph in 1972, the variation of lines of the ions Fe XII, Fe XI, Fe XV, Si X and S XII, Si IX and S XI is compared with the results of individual calculations for these ions, including theoretical intensities presented for Fe XII and Fe XI. Agreement is found to be good for Fe XII and reasonable for some of the lines of the other ions which in general are weaker in intensity. Several apparent anomalies are found however which may be due to unknown line components near the wavelengths observed.

Kastner, S. O.↗
NASA NTRS1978

Model for interpreting Doppler broadened optical line emission measurements on axially symmetric plasma

A plasma model, previously developed to interpret neutral-particle analyzer measurements on E x B heating devices, is adapted to analyze Doppler broadened charge-exchange-neutral lines measured by an optical monochromator. Comparison of theoretical with experimental results indicates that azimuthal drift as well as cyclotron motion are quite influential in determining line shapes and widths, and thus important in temperature determination, even when the monochromator line of sight is intersecting the plasma axis of symmetry. At this central sighting position, however, results are quite insensitive to radial ion density distribution when time lag between the charge-exchange-excitation events and emission is neglected. Line shapes and widths obtained by sighting across chords of plasma at various distances from the plasma axis of symmetry indicate a strong dependence on time lag.

Englert, G. W.↗
NASA NTRS1978

Emission-line spectra of two active regions on the solar limb - 1175-1940 A

Skylab emission-line spectra (1175 to 1940 A) of two active regions on the solar limb are examined. Electron densities for the active regions are derived using the intensity ratios of selected intersystem and allowed lines. The intensity ratios in the active regions are compared with those observed previously in quiet-sun and coronal-hole regions. The behavior of coronal forbidden lines relative to transition-zone lines is discussed along with the solar continuum intensities near and above the limb. These continuum intensities are then compared with those at similar slit positions for the quiet sun and the previously studied coronal hole. The active-region data are found to be consistent with either (1) multithermal loops with the high-temperature plasma occupying the tops of the loops or (2) nearly isothermal loops with the hotter loops extending to higher altitudes.

Feldman, U.↗
NASA NTRS1978

A simple formula for estimating Stark widths of neutral lines

A simple formula for the prediction of Stark widths of neutral lines similar to the semiempirical method of Griem (1968) for ion lines is presented. This formula is a simplification of the quantum-mechanical classical path impact theory and can be used for complicated atoms for which detailed calculations are not readily available, provided that the effective position of the closest interacting level is known. The expression does not require the use of a computer. The formula has been applied to a limited number of neutral lines of interest, and the width obtained is compared with the much more complete calculations of Bennett and Griem (1971). The agreement generally is well within 50% of the published value for the lines investigated. Comparisons with other formulas are also made. In addition, a simple estimate for the ion-broadening parameter is given.

Freudenstein, S. A.↗
NASA NTRS1978

Observation of the 63 micron (0 1) emission line in the Orion and Omega Nebulae

The 63 micron fine structure transition P4 : 3Pl yields 3P2 for neutral atomic oxygen was obtained during a series of flights at an altitude of approximately 13.7 km. In the Orion Nebula (M42), the observed line strength was 8 x 10 to the minus 15 power watt cm/2 which is estimated to be approximately 0.3 o/o of the energy radiated at all wavelengths. For the Omega Nebulae (M17), the line strength was 2.4 x 10 to the minus 15 power watt cm/2, and the fraction of the total radiated power was slightly higher. These figures refer to a 4' x 6' field of view centered on the peak for infrared emission from each source. The uncertainty in the line strength is approximately 50% and is caused by variable water vapor absorption along the flight path of the airplane. The line position estimate is 63.2 micron (+0.1, -0.2) micron. The prime uncertainty is due to the uncertain position of the (0 I) emitting regions in the field of view.

Melnick, G.↗
NASA NTRS1978

The 51.8 micron (0 3) line emission observed in four galactic H 2 regions

The (0 III) 51.8 microns line from four H II regions, M42, M17, W51 and NGC 6375A was detected. Respective line strengths are 7 x 10 to the minus 15 power, 1.0 x 10 to the minus 14 power, 2.1 x 10 to the minus 15 power and 2.6 x 10 to the minus 15 power watt cm/2. Observations are consistent with previously reported line position and place the line at 51.80 + or 0.05 micron. When combined with the 88.35 microns (0 III) reported earlier, clumping seems to be an important factor in NGC 6375A and M42 and to a lesser extent in W51 and M17. The combined data also suggest an (0 III) abundance of approximately 3 x 0.0001 sub n e' a factor of 2 greater than previously assumed.

Melnick, G.↗
NASA NTRS1979

A marching method for calculating line and continuum radiation in high energy flow fields

A method is presented for calculating nongrey radiative fluxes and intensities in a highly ionized, low temperature plasma with extreme line broadening. The method was developed to study radiative heating phenomena in the mass-injected hypersonic shock-layer environments characteristic of outer planet atmospheric entry, although it is not limited to such studies. The radiative properties model assumed local thermodynamic equilibrium and used standard continuum and molecular band models. The atomic line model, however, used a frequency-marching method for the frequency integration, which not only accounted completely for line overlapping (reabsorption) effects, but compared favorably in economy with the best equivalent-width methods. An assessment of hydrogen line-far-wing treatments, with recommendations for engineering models, is also presented.

Bolz, C. W., Jr.↗
NASA NTRS1978

Measurement of the profile and intensity of the solar He I lambda 584-A resonance line

The intensity and profile of the helium resonance line at 584 A from the entire disk of the sun was investigated by using a rocket-borne helium-filled spectrometer and a curve-of-growth technique. The line profile was found to be accurately represented by a Gaussian profile with full width at half maximum of 122 + or - 10 mA, while the integrated intensity was measured to be 2.6 + or - 1.3 billion photons/s per sq cm at solar activity levels of F(10.7) = 90.8 x 10 to the -22nd per sq m/Hz and Rz = 27. The measured line width is in good agreement with previous spectrographic measurements, but the integrated intensity is larger than most previous photoelectric measurements. However, the derived line center flux of 20 + or - 10 billion photons/s per sq cm/A is in good agreement with values inferred from airglow measurements.

Maloy, J. O.↗
NASA NTRS1979

51.8 micron forbidden O III line emission observed in four galatic H II regions

The 51.8-micron forbidden O III line has been detected in four H II regions: M42, M17, W51, and NGC 6357A. The respective line strengths are 7 x 10 to the -15th, 1.0 x 10 to the -14th, 2.1 x 10 to the -15th, and 2.6 x 10 to the -15th W/sq cm. The observations are consistent with a previously reported line position and place the line at 51.80 + or - 0.05-micron. When combined with the 88.35-micron forbidden O III observations reported earlier, clumpiness is found to be an important factor in NGC 6357A and M42 and nonnegligible in W51 and M17. The combined data also suggest an O III abundance of about 0.0003 times the electron density, which is a factor of 2 greater than a number of investigators have reported.

Melnick, G.↗
NASA NTRS1979

A survey of ultraviolet circumstellar absorption lines in the spectra of early Be and shell stars

Copernicus UV data are used to examine the rich shell absorption spectra between 1120 and 1140 A in 17 Be and shell stars. Previous observations of the program stars are reviewed, the general appearance of the shell spectra between 1120 and 1140 A is described, and the shell spectra are compared with the spectra of four bright B-type supergiants in the same wavelength region. The line strengths are analyzed to determine quantitative shell strengths and shell column densities; the shell line velocities are discussed in the context of different models. It is shown that UV shell lines can exist in stars with no visible-wavelength shell features, that Fe III shell lines dominate the spectra between 1120 and 1140 A in Be and shell stars with circumstellar absorption features, and that the spectra of Be and shell stars in this region strongly resemble those of supergiants of similar effective temperature.

Snow, T. P., Jr.↗
NASA NTRS1978

Radio-frequency heating of emission-line gas near compact extragalactic radio sources

High-brightness-temperature radio sources significantly heat by free-free absorption any nearby gas that has properties similar to those inferred for QSO emission-line gas. As a result, the outer layers of the gas clouds expand, and their visible line emission decreases. Moderate heating enhances the collisionally excited ultraviolet line of O VI at 1034 A. Stronger heating penetrates the entire cloud and extinguishes all lines. Strong enough radio fluxes cause a thermal instability by stimulated Compton heating that is only saturated by Compton cooling at very high temperatures. It is speculated that BL Lac objects differ from quasars by having higher radio turnover frequencies, lower gas pressures, or more violent variability, all of which make radio heating more effective.

Krolik, J. H.↗
NASA NTRS1979

On the nonthermal excitation and polarization of X-ray lines during solar flares

The energy distributions of nonthermal electrons are derived from hard X-ray spectra taken during the impulsive phase of two 2B flares in February 1969. They are used to calculate the fluxes of nonthermally excited X-ray lines of hydrogen-like and helium-like ions. These fluxes are compared to the total line fluxes observed at the same time with crystal spectrometers. The nonthermal excitation is found to give only small contributions to the total line intensities. This implies that the impact polarization which is to be expected for anisotropic velocity distributions of the energetic electrons, will be low. Nevertheless it should be feasible to detect line polarization during the impulsive phase of strong X-ray flares.

Haug, E.↗
NASA NTRS1979

Base line estimation using single passes of laser data

The laser data of the GEOS 3 satellite passes observed by four stations at Greenbelt (Maryland), Bermuda, Grand Turk Island (Bahamas) and Patrick Air Force Base (Florida), were employed to determine precise interstation base lines and relative heights in short orbital arcs of no more than 12-min duration. No more than five arcs of data are required to define the interstation base lines to 30-cm precision. Base lines running parallel to the orbital motion can be defined to submeter precision from a single short arc of data. Combining arcs of different orbital geometry in a common adjustment of two or more stations relative to the base station helps to compensate for weak base line definition in any single arc. This technique can be used for tracking such spacecraft as Lageos, a high-altitude retroreflector-carrying satellite designed for precise laser ranging studies.

Dunn, P. J.↗
NASA NTRS1979

X-ray line emission from the Tycho supernova remnant

The observation of the X-ray spectrum of the Tycho supernova remnant in the energy range 0.5 to 20 keV is discussed. Four significant line features in the spectrum: The K alpha lines of silicon, sulphur, and iron; and the L lines of iron are examined. Comparisons between the silicon and sulphur equivalent widths and K alpha iron line energies of Tycho and Cas A are discussed. Suggest that the X-ray emitting plasma in Tycho is further from collisional ionization equilibrium than that of Cas A.

Pravdo, S. H.↗
NASA NTRS1980

Submillimeter, millimeter, and microwave spectral line catalogue

A computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between O and 3000 GHz (such as; wavelengths longer than 100 m) is discussed. The catalogue was used as a planning guide and as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue was constructed by using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances.

Poynter, R. L.↗
NASA NTRS1979

Observations of emission lines in M supergiants

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Lambert, D. L.↗
NASA NTRS1979

Observations of far-infrared fine structure lines - Forbidden O III 88.35 microns and forbidden O I 63.2 microns

Results are presented for observations of the fine-structure lines of forbidden O III at 88.35 microns and forbidden O I at 63.2 microns in a number of sources by means of an airborne far-IR spectrometer. The sources M17, NGC 7538, and W51 are mapped in the forbidden O III line with a resolution of 1 arcmin, and the emission peak is found to coincide with the maximum radio continuum in all cases. The far-IR continuum is simultaneously mapped where possible; the continuum peak is shown to be distinct from the center of ionization in the same three sources. The forbidden O III line is also detected in W3, W49, and several positions in M42 (Orion). The forbidden O I line is detected in M17, in M42, and marginally in DR 21. An unsuccessful search for the J = 1-0 transition of HD at 112 microns in the direction of the Kleinmann-Low nebula is also reported.

Storey, J. W. V.↗