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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Gamma-ray lines from interstellar grains

The letter points out the existence of a hitherto unknown component of gamma-ray line emission: very narrow (FWHM less than 5 keV) lines from interstellar grains. 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 NTRS1977

Emission measures, electron densities, and nonthermal velocities from optically thin UV lines near a quiet solar limb

Calibrated intensities and line widths are presented for 45 optically thin chromospheric and transition-zone UV lines observed in a quiet area near the solar limb. The observations were made over the wavelength range from 1175 to 1915 A with the slit spectrograph on the Skylab Apollo Telescope Mount. Three nonthermal-velocity components are derived from the transition-zone line widths: a main component of 23 km/s and two high-velocity components of 45 and 75 km/s, respectively, which contribute 5% to 10% of the averaged intensity. Absolute intensities are determined as a function of height, emission measures are obtained as functions of height as well as temperature, and electron densities are estimated from density-sensitive line ratios. The densities estimated from different sets of lines are found not to agree with each other, but the values obtained from the Si III multiplet between 1297 and 1301 A are considered to be the most reliable. An atmospheric model with inhomogeneous structures extending high above the solar surface is suggested.

Moe, O. K.↗
NASA NTRS1977

X-ray spectra of Hercules X-1. I - Iron line fluorescence from a subrelativistic shell

The X-ray spectrum of Her X-1 was observed in the energy range from 2 to 24 keV from August 29 to September 3, 1975. Emission features are observed near the K-alpha iron-line energy which exhibit both broadening and a double line structure. The total luminosity in these features is about 4 by 10 to the 35th power ergs/s. Iron line fluorescence from an opaque cool (not exceeding 1 million K) shell of material at the Alfven surface provides the necessary luminosity in this feature. The double line structure and the line energy width can be due to Doppler shifts if the shell is forced to corotate with the pulsar at a radius of at least 800 million cm. Implications of this model regarding physical conditions near Her X-1 are discussed.

Pravdo, S. H.↗
NASA NTRS1978

Solution of axisymmetric and two-dimensional inviscid flow over blunt bodies by the method of lines

Comparisons with experimental data and the results of other computational methods demonstrated that very accurate solutions can be obtained by using relatively few lines with the method of lines approach. This method is semidiscrete and has relatively low core storage requirements as compared with fully discrete methods since very little data were stored across the shock layer. This feature is very attractive for three dimensional problems because it enables computer storage requirements to be reduced by approximately an order of magnitude. In the present study it was found that nine lines was a practical upper limit for two dimensional and axisymmetric problems. This condition limits application of the method to smooth body geometries where relatively few lines would be adequate to describe changes in the flow variables around the body. Extension of the method to three dimensions was conceptually straightforward; however, three dimensional applications would also be limited to smooth body geometries although not necessarily to total of nine lines.

Hamilton, H. H., II↗
NASA NTRS1978

Analysis of the emission line spectra of a solar flare observed from Skylab

Skylab observations in the EUV spectra made with the NRL split spectrograph during the Sept. 5, 1973 flare have revealed that chromospheric and transition zone lines were enhanced, especially the allowed lines. Greatest enhancement was noted in the Ni II and P II lines (by a factor of 800). The chromospheric lines maintain their sharp and Gaussian profiles and are not appreciably broadened. The transition zone lines, however, show a red shifted component during the initial phase of the flare. Turbulent downward mass motions are observed, probably due to the imbalance between hot flare plasma (13 x 10 to the 6th K) and cooler plasma (10 to the 5th K). High density is recorded in the transition zone, whose thickness, therefore, is deduced to be small.

Cheng, C.-C.↗
NASA NTRS1978

Search for X-ray line emission from Cassiopeia A

The large area graphite crystal spectrometer aboard OSO 8 has been used to search for X-ray line emission from Cas A from ions of Si, S, and Fe over the energy band 1.865 to 8 keV. No evidence was obtained for line emission. The upper limits for the Si and S line fluxes are used to establish upper limits on the abundances of these elements. The limit on the Fe line flux is consistent with the strength of the emission feature reported in proportional counter experiments. Questions of nonequilibrium in ionization in Cas A and the effects on X-ray line emission are considered.

Kestenbaum, H. L.↗
NASA NTRS1978

Ultraviolet observations of cool stars. VI - L alpha and Mg II emission line profiles /and a search for flux variability/ in Arcturus

High-precision, high-resolution profiles of the L alpha and Mg II k chromospheric emission lines from Arcturus (alpha Boo) obtained with the Princeton Experimental Package aboard the Copernicus satellite are presented. Asymmetries seen in the profiles of these lines are probably intrinsic to the star, rather than the result of interstellar absorption. In contrast to previous observations of the Ca II K emission line, no evidence is found during a three-year period for variability in the profiles or in the total fluxes from these lines on time scales ranging from hours to months. Also presented is a flux profile of the O I 1302 line and flux upper limits for L beta, O VI 1032, Si III 1206, and O V 1218.

Mcclintock, W.↗
NASA NTRS1978

A study of the absorption-line spectra of six high-redshift quasi-stellar objects

High-resolution spectrograms of six QSOs with apparent visual magnitudes of 17.0 to 18.5 and redshifts greater than 2 are studied for absorption lines. Accurate wavelengths are measured for all the absorption lines that could be detected, attempts are made to identify redshift systems, and the redshifts in each object are examined. Analysis of the absorption-line spectra shows that: (1) a large number of redshifts covering a wide range of values are present in five of the QSOs; (2) about two-thirds of the absorption lines remain unidentified, cannot be of Galactic origin, and are not associated with existing redshift systems; (3) many comparatively small absorption redshifts exist which, if they are due to intervening galaxies, must be produced by very large halos; and (4) in one QSO there is a possible redshift system containing five lines with an absorption redshift that is significantly greater than the emission redshift.

Roberts, D. H.↗
NASA NTRS1978

Approximate line shapes for hydrogen

Two independent methods are presented for calculating radiative transport within hydrogen lines. In Method 1, a simple equation is proposed for calculating the line shape. In Method 2, the line shape is assumed to be a dispersion profile and an equation is presented for calculating the half half-width. The results obtained for the line shapes and curves of growth by the two approximate methods are compared with similar results using the detailed line shapes by Vidal et al.

Sutton, K.↗
NASA NTRS1979

Observations of far-infrared fine structure lines: o III88.35 micrometer and oI 63.2 micrometer

Observations of the O III 88.35 micrometer line and the O I63.2 micrometer were made with a far infrared spectrometer. The sources M17, NGC 7538, and W51 were mapped in the O III line with 1 arc minute resolution and the emission is found to be quite widespread. In all cases the peak of the emission coincides with the maximum radio continuum. The far infrared continuum was mapped simultaneously and in M17, NGC 7538, and W51 the continuum peak is found to be distinct from the center of ionization. The O III line was also detected in W3, W49, and in a number of positions in the Orion nebula. Upper limits were obtained on NGS 7027, NGC 6572, DR21, G29.9-0.0 and M82. The 63.2 micrometer O I line was detected in M17, M42, and marginally in DR21. A partial map of M42 in this line shows that most of the emission observed arises from the Trapezium and from the bright optical bar to the southeast.

Storey, J. W. V.↗
NASA NTRS1979

System for automatically switching transformer coupled lines

A system is presented for automatically controlling transformer coupled alternating current electric lines. The secondary winding of each transformer is provided with a center tap. A switching circuit is connected to the center taps of a pair of secondary windings and includes a switch controller. An impedance is connected between the center taps of the opposite pair of secondary windings. The switching circuit has continuity when the AC lines are continuous and discontinuity with any disconnect of the AC lines. Normally open switching means are provided in at least one AC line. The switch controller automatically opens the switching means when the AC lines become separated.

Dwinell, W. S.↗
NASA NTRS1978

Spatial structure in lines in the 3398-3526 A region at the extreme limb - Observation, identification and interpretation

Spectrograms of high spatial and spectral resolution have been obtained of the extreme solar limb, using the vacuum tower telescope of Sacramento Peak Observatory. Emission lines in the range 3398-3526 A have been identified and classified according to intensity, spatial structure (intensity variation), and profile. Some lines show spatial intensity variation; others do not. It is shown that this effect is related to the abundance of the element responsible for the line and the mean lower-level excitation potential of interlocked lines. This effect is explained in terms of radiative interlocking with other lines, as well as the characteristic size of the volume contributing to the mean intensity.

Canfield, R. C.↗
NASA NTRS1978

Si XIII and Si XIV line emission search with the ANS crystal spectrometer

The final results of the search for Si XIII and Si XIV line emission, using the ANS Bragg crystal spectrometer, are presented. No positive line detection was achieved in any of the measurements made on several types of cosmic object; i.e., a transient X-ray source, close binary systems, supernova remnants, GX sources, and clusters of galaxies. Three-sigma upper limits for discrete line emission from these objects are reported and compared with line strengths inferred from other proportional-counter and Bragg spectrometer data. The present upper limit of 1.0 eV for the equivalent width of a narrow Si XIV line emission from the X-ray nova A0620-00 is an order of magnitude lower than previous limits set by other experiments.

Parsignault, D. R.↗
NASA NTRS1978

Silicon X-ray line emission from solar flares and active regions

New observations of solar flare and active region X-ray spectra obtained with the Columbia University instrument on OSO-8 are presented and discussed. The high sensitivity of the graphite crystal panel has allowed both line and continuum spectra to be served with moderate spectral resolution. Observations with higher spectral resolution have been made with a panel of pentaerythritol crystals. Twenty-nine lines between 1.5 and 7.0 A have been resolved and identified, including several dielectronic recombination satellite lines to Si XIV and Si XIII lines which have been observed for the first time. It has been found that thermal continuum models specified by single values of temperature and emission measure have fitted the data adequately, there being good agreement with the values of these parameters derived from line intensity ratios.

Parkinson, J. H.↗
NASA NTRS1979

The role of O-type neutral lines in magnetic merging during substorms and solar flares

A model has been constructed for the magnetic field configuration of a combination of X- and O-type neutral lines in the middle of the geomagnetic tail. The main feature is a bubble centered on the O-type line, the field lines of which are not connected to the main geomagnetic field. An analytical model of the motion of charged particles in the vicinity of an O-type neutral line, with an electric field aligned parallel to it, has been constructed and analyzed. Finally it is found that two distinct mechanisms of particle acceleration may exist if a substorm is powered by the inductive emf generated when the tail's magnetic field returns to a more dipolelike configuration by flowing through a pair of X- and O-type neutral lines.

Stern, D. P.↗
NASA NTRS1978

Physical conditions in the emission-line regions of BL Lac objects and QSOs

BL Lac objects have weak emission lines because of the absence of even a small amount (about 1 solar mass) of gas at high densities. The large forbidden N II/H-alpha intensity ratio of BL Lac indicates that a substantial mass (at least about 1000 solar masses) of gas is present, with a high nitrogen abundance. The broad line profiles of QSOs and Sy 1 galaxies are difficult to understand in terms of infall or orbital motion, but are consistent with outflow possibly resulting from radiation pressure. The asymmetries of the line profiles are a natural consequence of self-absorption in the outflowing clouds. Over a wide range in luminosity, the radius of the broad-line region adjusts itself so that the incident flux is the same; the regulation mechanism may involve the evaporation of refractory grains. The ratio of radiation flux to gas density also is constant over a wide range of luminosity, and this can be understood in terms of radiation pressure. The absence of strong emission lines in BL Lac objects may be related to the geometry of an accretion flow that fuels the luminosity.

Shields, G. A.↗
NASA NTRS1979

The ratio of deuterium to hydrogen in interstellar space. IV - The lines of sight to Delta, Epsilon, and Iota Orionis

Deuterium absorption features in spectra of Delta, Epsilon, and Iota Ori obtained with Copernicus are analyzed. The Iota Ori line-of-sight analysis, which is quite detailed because of the high-velocity H I components superposed on the deuterium features, gives a D/H ratio (which is uncertain because of a complex profile) of 0.000014. A D/H ratio of the order of 7 millionths is determined for Delta and Epsilon Ori. For the complex line profiles involved, one may regard this as a formal lower limit. Several attempts were made to increase the ratio N(D I)/N(H I) in the context of reasonable models for the line of sight, but with no success; the derived values are therefore regarded as actual values, not lower limits. Since the derived value is an average on the line of sight, the possibility cannot be ruled out that the true ratios N(D I)/N(H I) in individual nearby components differ from the mean values. The mean value for these two directions is lower by a factor of 4 than the best value for the Zeta Pup line of sight (the highest yet derived for path lengths greater than 50 pc).

Laurent, C.↗
NASA NTRS1979

Velocity profiles of the 2.1 micron H2 emission line in the Orion molecular cloud

Spectra of the H2 nu = 1-0 S(1) emission line in Orion, observed at various positions with a resolution of 20 km/s, are presented. The intrinsic full width at half-maximum of the line ranges from 18 to 58 km/s over the observed positions. Analysis of the line profiles shows that the emitting gas is probably expanding from a region near the BN and KL infrared sources at velocities typically of 40 km/s but as high as 100 km/s, and that it is associated with the source of the broad lines seen in the spectra of many other molecules. Strong constraints are placed on models of the physical processes responsible for the broad emission lines.

Nadeau, D.↗