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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

On spatial variations in the intensity of chromospheric H-alpha

Investigation of the formation of patterns in H-alpha spectroheliograms and filtergrams. Introducing a source-sink-control diagram, it is concluded that the H-alpha line source function in the quiet solar chromosphere is indirectly controlled by the photospheric radiation fields in the Balmer and Paschen continua. It is demonstrated that in producing the observed patterns, horizontal spatial variations in the shape of the absorption profile are extremely effective compared to changes in the source and sink terms. Applying this mechanism, asymptotic values are computed for the contrasts and visibilities in chromospheric H-alpha.

Gebbie, K. B.↗
NASA NTRS1974

Absorption of laser radiation in a H-He plasma. I - Theoretical calculation of the absorption coefficient

The theory for calculating the absorption of laser radiation by hydrogen is outlined for the temperatures and pressures of common laboratory plasmas. Nonhydrogenic corrections for determining the absorption by helium are also included. The coefficients for the absorption of He-Ne laser radiation at the wavelengths of 0.633, 1.15, and 3.39 microns in a H plasma is presented for temperatures in the range from 10,000 to 40,000 K and electron number densities in the range from 10 to the 15th power to 10 to the 18th power per cu cm. The total absorption of a H-He plasma calculated from this theory is compared with the measured absorption. The theoretical composition of the H-He absorption is analyzed with respect to the significant absorption processes, inverse bremsstrahlung, photoionization, resonance excitation, and photodetachment.

Stallcop, J. R.↗
NASA NTRS1975

Abundance of Fe relative to H at 1.5 solar radii

The abundance of Fe relative to H is obtained by using resonantly scattered intensities of lambda 284 of Fe XV that were measured with OSO-7 and resonantly scattered intensities of L-alpha of H I that were obtained by Gabriel (1971). Because of possible differences in electron densities along lines of sight for these non-simultaneous measurements and in relative calibrations, results are rather uncertain but still indicate that the average Fe abundance relative to H in the corona appears to be at least as large as a recent photospheric abundance. Some limitations in using this method for obtaining abundances are examined for future experiments with simultaneous measurements and well calibrated detectors.

Nakada, M. P.↗
NASA NTRS1976

Radio continuum measurements of compact H II regions and other sources

Results are reported for measurements of the flux densities of 33 sources at wavelengths of 13, 4, and 2 cm, which were conducted using the NASA/JPL Deep Space Network 64-m antenna at Goldstone, Calif. Besides compact H II regions, the sources included five Uhuru X-ray sources, several IR sources, an extragalactic radio source, and a H2O maser. The Lyman continuum flux is derived from the measured radio flux and the assumed distance and temperature for 10 possible H II regions; the spectra of previously known sources are extended to higher frequencies, and upper limits are placed on the flux densities for the five X-ray sources. New compact H II regions are found in the bright nebula M78, the nebula K5, and the Ophiuchus dark cloud/IR region.

Matsakis, D. N.↗
NASA NTRS1976

J, H, K photometry of 433 Eros and other asteroids

Results are reported for IR photometry of nine bright asteroids, including 433 Eros, which was conducted in the J, H, K, and (for Eros) L bands with an InSb photometer on the 1.3-m Kitt Peak telescope. It is found that the J-H and H-K color indices of all nine asteroids are slightly redder than those of the sun and that three C-type objects are somewhat redder in the same color indices than four S-types and an E-type. Eros is shown to have an unusually red J-K index; the shape of its IR spectral reflectance curve is attributed in part to the presence of the weak 2-micron pyroxene absorption band in the spectrum. The results show that JHK photometry is less diagnostic of asteroidal composition than higher-resolution IR spectrophotometry.

Chapman, C. R.↗
NASA NTRS1977

Analysis of H-alpha flare spectra

Spectrographs of the H-alpha line taken at 15 second intervals from the event of 5 Sept. 1973 were interpreted by comparison with synthetic profiles. A sequence of 27 high resolution H alpha profiles was obtained from the second brightest flare kernel. The profiles were generally self reversed with a maximum peak intensity of 1.16 x continuum and a maximum central intensity of .91 x continuum. The line characteristics such as red and violet peak intensities and positions, center shifts and wing intensities were tabulated. Synthetic H-alpha profiles were generated from a finite layer assuming simple parameteric forms for the source function and velocity field. The velocity chosen always decreased with optical depth and had the same sign. For absorption profiles, bisector shifts were calculated for a variety of velocities. The velocity field and source function were derived as a function of optical depth and time.

Kulander, J. L.↗
NASA NTRS1977

Measurements of line emission in quiescent prominences - Ca/+/, H and He

The paper presents observations of Ca(+) H, K, and infrared-triplet integrated line intensities, as well as H-beta, H-gamma and He 5876-A throughout eight quiescent prominences. The data were obtained with a multichannel coronal spectrophotometer system. The presently available theoretical models appear to be insufficient to provide a consistent basis for the interpretation of the data.

Landman, D. A.↗
NASA NTRS1976

Solar wind H-3 and C-14 abundances and solar surface processes

Tritium is measured as a function of depth in a Surveyor 3 sample. The upper limit for solar-wind-implanted tritium gives an H-3/H-1 limit for the solar wind of 10 to the -11th power. The temperature-release patterns of C-14 from lunar soils are measured. The C-14 release pattern from surface soils differs from a trench-bottom soil and gives positive evidence for the presence of C-14 in the solar wind with a C-14/H-1 ratio of approximately 6 by 10 to the -11th power. This C-14 content fixes a minimal magnitude for nuclear processes on the solar surface averaged over the past 10,000 yr. The H-3 and C-14 contents combine to require that either the mixing rate above the photosphere be rapid or that the H-3 produced by nuclear reactions be destroyed by secondary nuclear reactions before escaping in the solar wind.

Fireman, E. L.↗
NASA NTRS1977

3.5 mm depression features associated with H-alpha 'disparitions brusques'

The characteristics of 3.5-mm depression features associated with two 'disparation brusques' observed in H-alpha are discussed. The millimeter depressions still exist, although reduced in strength, after the disappearance of the H-alpha filament. The two depressions correspond to temperatures of 600 and 450 K before and to 200 and 250 K after the disappearance of the H-alpha filament.

Kundu, M. R.↗
NASA NTRS1978

Requisite temperatures for the stabilization of atomic H in solid H2

If an atomic hydrogen/molecular hydrogen propellant containing at least 15% free H atoms by weight may be used, values for the theoretical specific impulse near and above 750 s may be predicted. The tritium-impregnation concept has been applied to manufacturing such an H/H2 propellant, and a phenomenological rate process theory has been derived for the matrix-isolation storage and equilibrium stability of atomic H produced at such ultralow temperatures in tritium-impregnated H2. It is suggested that an energy storage efficiency greater than 0.30 may be obtained at temperatures below 100 mK. So that the storage of atomic H is stable with respect to arbitrary small perturbations, the surface temperature must be less than a critical value dependent on sample volume, tritium weight fraction, and energy storage efficiency. A derivation of the formula for this critical surface temperature is presented, noting that the energy storage efficiency is to be fixed by experiment.

Rosen, G.↗
NASA NTRS1978

Far-infrared observations of H II regions near the galactic center

This paper presents and discusses far-infrared observations of nine H II regions within 1 deg of the galactic center, including Sgr A, Sgr B2, Sgr C, and G0.5-0.0. The far-infrared luminosity, color temperature, and optical depth of these regions and the ratio of infrared flux to radio-continuum flux lie in the range characteristic of spiral-arm H II regions. The far-infrared results are therefore consistent with the idea that the galactic-center H II regions are ionized by luminous early-type stars. Steep systematic gradients in far-infrared color temperature and optical depth are seen along the galactic plane between Sgr B2 and G0.5-0.0; the appearance of this area is similar to that of regions of star formation in the spiral arms.

Gatley, I.↗
NASA NTRS1978

Mg II h and k emission from luminous M stars

Mg II h and k emission lines of the M2 giant beta Peg and the M5 supergiant alpha Her were detected in Copernicus observations. In the alpha Her profiles, similar to alpha Ori and alpha Sco profiles, the k line is asymmetric and the h line is symmetric. The possibility that the k line asymmetry is produced by overlying absorption is discussed. In beta Peg, both h and k lines are asymmetric, and line formation in an expanding chromosphere is indicated. The observations are in accord with one formulation of the Wilson-Bappu relation but deviate from another form of the Wilson-Bappu relation.

Bernat, A. P.↗
NASA NTRS1978

A survey of interstellar H I from L-alpha absorption measurements. II

This paper presents interstellar H I column densities, mean H I space densities, total neutral hydrogen column densities, and total mean hydrogen space densities toward 100 stars surveyed in the L-alpha region with the U2 detector of the Copernicus satellite. The data for 47 stars are compared with OAO 2 results, and ratios of gas to E(B-V) color excess are computed for 30 'intercloud' stars, 45 'cloud' stars, and the combined sample of 75 stars. A definitive value of 5.8 x 10 to the 21st power atoms/sq cm per mag is obtained for the mean ratio of total neutral hydrogen to color excess, indicating that this ratio seems to be a constant, independent of location in the sky, except possibly toward stars with anomalous extinction. The anomalous ratio determined for Rho Oph is examined, and the galactic distribution of neutral hydrogen is evaluated. The following values are estimated for matter in the galactic plane within 500 pc of the sun: a total mean hydrogen space density of 1.15 atoms/cu cm, a mean H2 space density of 0.143 molecule/cu cm (possibly a lower limit), and a mean H I space density of 0.86 atom/cu cm (a possible overestimate).

Bohlin, R. C.↗
NASA NTRS1978

Far-infrared observations of Large Magellanic Cloud H II regions

Far-infrared emission has been measured from four Large Magellanic Cloud H II regions: the 30 Doradus nebula, MC75, MC76 and MC77. The far-infrared radiation is thermal emission from dust heated by starlight. The results show that the LMC H II regions, like H II regions in the Galaxy, have far-infrared luminosities comparable to the total luminosity of their exciting stars.

Werner, M. W.↗
NASA NTRS1979

Implications of high-velocity interstellar H I absorption features

Contributions to the interstellar H I column density at high velocities from immediate postshock gas and from the cooling gas behind a shock are compared. The detection of high-velocity H I in L-epsilon and L-delta for Iota Ori is reported and interpreted as cooling gas behind a shock of 100 km/s velocity. The immediate postshock gas should be observable for shock velocities greater than 200 km/s and permits direct determination of the velocities of adiabatic shocks in the interstellar medium. It is pointed out that interstellar L-alpha and L-beta lines may not have purely Lorentzian profiles if high-velocity H I is a widespread phenomenon.

Cowie, L.↗
NASA NTRS1980

Solar limb emission lines near Ca II H & K and their spatial intensity variations

The paper employs solar observations of high spatial and spectral resolution to identify emission lines seen in the extended wings of Ca II H & K near the solar limb. Emission lines in the wings of H & K represent valuable diagnostics of the atmospheres of cool stars, with a varying information content which depends on their particular formation mechanism. In solar spectrograms different emission line formation mechanisms can be distinguished by the character of the spatial intensity variation (SIV) apparent in the lines. Various classes of H & K emission features, their spatial intensity variations and their formation mechanisms (of which some pose further problems) are discussed. A new extended list of line identifications is compiled based on their formation class and compared with other line lists. Evidence is found that stellar luminosity-sensitive lines tend to show large spatial intensity variation on the sun.

Rutten, R. J.↗
NASA NTRS1980

Extended hopane derivatives in sediments - Identification by H-1 NMR

Sedimentary C32 hopanoic acid, one of the most abundant in nature and of probable bacterial origin, has been isolated for the first time as a single component and characterized by H-1 NMR. The 17 alpha H, 21 beta H configuration of the C31 alkane has been similarly confirmed.

Taylor, J.↗
NASA NTRS1980

Radial accretion of H-rich material onto a He white dwarf

The nova outburst is modeled by spherically accreting H-rich material onto a 1 solar mass He white dwarf at a rate of 10 to the -8th solar mass/yr. The star accretes for 5848 years, when the nuclear reactions run away near the base of the accreted envelope. The nuclear-energy generation rate rises to 4.6(8) solar luminosities, and the envelope expands in response to it. However, nova-like mass ejection does not occur because the envelope is of insufficient mass, the base of the envelope is only mildly electron degenerate, and there is no enrichment of the CNO abundance. To overcome these limiting conditions, it is suggested that the H-rich material be accreted either more slowly than 10 to the -10th solar mass/yr or with angular momentum. Outbursts resulting in the former case should be similar to the nova models computed by Starrfield, Truran, and Sparks. Outbursts in the latter case should be strengthened, and novae might result because the H-rich material will be mixed into the surface layers of the white dwarf, as first suggested by Kippenhahn and Thomas (1978).

Kutter, G. S.↗