Search NASA⌕ Search

SEARCH · Search NASA

Results for “Lambda”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Measurements of quiescent prominence spectra - Ca/+/ double-lambda 8542, 8498 and He lambda 4471, Ti/+/ lambda 4468

High-dispersion measurements of the line profiles of the Ca(+) lines at 8542 and 8498 A and the He 4471-A, Ti(+) 4468-A line pair in the spectra of quiescent solar prominences are presented. The measured Ca(+) and He line profiles are found to be accurately described by the two-component model of Landman et al. (1977) and Landman and Mongillo (1979) in which the prominence along the line of sight consists of a low-temperature region surrounded by high-temperature material representing contributions from the prominence/corona interface; the Ti(+) lines are too weak to distinguish among different models. The Ca(+) data allow a constant infrared line source function for the low-temperature region of 50,000 ergs/sq cm per sec per ster per A to be calculated, which is in disagreement with the previous Ca(+) excitation equilibrium calculations but is consistent with generally accepted values of the electron density and temperature. The integrated intensity ratio of 0.048 between Ti(+) and He emission indicates a low-temperature region temperature of 6620 K and microturbulence of 5.1 km/sec and high-temperature microturbulence of 11 km/sec for Ca(+) and 20 km/sec for He. The results exclude macroturbulence as a possible explanation of the generally observed wing enhancements.

Landman, D. A.↗
NASA NTRS1992

Non-LTE radiative transfer with lambda-acceleration - Convergence properties using exact full and diagonal lambda-operators

We investigate the convergence properties of Lambda-acceleration methods for non-LTE radiative transfer problems in planar and spherical geometry. Matrix elements of the 'exact' A-operator are used to accelerate convergence to a solution in which both the radiative transfer and atomic rate equations are simultaneously satisfied. Convergence properties of two-level and multilevel atomic systems are investigated for methods using: (1) the complete Lambda-operator, and (2) the diagonal of the Lambda-operator. We find that the convergence properties for the method utilizing the complete Lambda-operator are significantly better than those of the diagonal Lambda-operator method, often reducing the number of iterations needed for convergence by a factor of between two and seven. However, the overall computational time required for large scale calculations - that is, those with many atomic levels and spatial zones - is typically a factor of a few larger for the complete Lambda-operator method, suggesting that the approach should be best applied to problems in which convergence is especially difficult.

Macfarlane, J. J.↗
NASA NTRS1973

Telluric lines in the region lambda lambda 6327.5-6330.0 angstrom angstrom

The solar spectrum region lambda lambda 6327.5 to 6330.0 AA was investigated. Six new telluric lines were found. The behavior of two of them (lambda 6328.51 and lambda 6328.71 A) is the same as identified molecular oxygen lines in the region. The lines lambda 6328.27, 6329.12, and 6329.29 A are more intensive when there are days with high humidity.

Alikayeva, K. V.↗
NASA NTRS1993

Dynamic processes in Be star atmospheres. I - 'Dimple' formation in the He I lambda 6678 line of lambda Eridani

Several examples of weakenings of the C IV and N V resonance lines are found to coincide with the appearance of lambda 6678 dimples. The absence of variations in other UV lines and in the UV continuum at the same time or nearly the same time argues against dimples being caused by thermal variations from the underlying star. It is instead suggested that the resonance line weakenings are caused by non-LTE effects associated with the condensation of high density structures at some elevation over the star. A simple model of an opaque, essentially stationary slab which backscatters lambda 6678 line radiation into a surrounding 'penumbral' region is presented. Lambda 6678 photons are scattered a second time in this region back into the observer's line of sight and in the process acquire the local projected Doppler shift from rotation. Slabs would probably produce too little emission to be easily detected in the H alpha profile. Their detection in strong He I lines seems the best strategy among early Be stars.

Smith, Myron A.↗
NASA NTRS1987

The (C III lambda 1909/Si III lambda 1892) ratio as a diagnostic for planetary nebulae and symbiotic stars

Suitable IUE archival material on planetary nebulae has been examined to determine the log R /F(lambda 1909 C III)/F(lambda 1892 Si III)/ as a discriminant for distinguishing planetary nebulae from symbiotic stars and related objects. The mean value of log R for 73 galactic planetaries is 1.4, while that of extragalactic planetaries appears to be slightly lower, and that for symbiotics is 0.3. The lower value of log R for symbiotics is easily understood as a consequence of their higher densities. A plot of log R versus N-epsilon indicates that 80 percent of the planetaries fall into the range of log R between 1.2 and 1.8, but some of the 'peculiar' and bipolar nebulae fall below log R = 1.2. The corresponding N(C++)/N(Si++) ionic ratio varies over a large range.

Feibelman, Walter A.↗
NASA NTRS1995

The origin of N III lambda 990 and C III lambda 977 emission in AGN narrow-line region gas

We discuss implications of Hopkins Ultraviolet Telescope (HUT) detections of C III lambda 977 and N III lambda 990 emission from the narrow-line region of the Seyfert 2 galaxy NGC 1068. In their discovery paper Kriss et al. showed that the unexpectedly great strength of these lines implies that the emitting gas must be shock-heated if the lines are collisionally excited. Here we investigate other processes which excite these lines in photoionization equilibrium. Recombination, mainly dielectronic, and continuum fluorescence are strong contributors to the line. The resulting intensities are sensitive to the velocity field of the emitting gas and require that the turbulence be of the same order of magnitude as the observed line width. We propose optical observations that will decide whether the gas is collisionally or radiatively heated.

Ferguson, J. W.↗
NASA NTRS1995

Moderate-resolution spectral standards from lambda 5600 to lambda 9000

We present a grid of stellar classification spectra of moderate resolution (R approximately 1500) in the range lambda lambda 5600-9000 A, compiled from high signal-to noise spectra of 275 stars, most in the open clusters Praesepe and M67. The grid covers dwarfs from types B8 through M5, giants from G8 through M7, and subgiants from F5 through K0. We catalog atomic and molecular absorption features useful for stellar classification, and demonstrate the use of luminosity-sensitive features to distinguish between late-type dwarf and giant stars. The entire database is made available in digital format on anonymous ftp and through the World Wide Web.

Allen, Lori E.↗
NASA NTRS1999

T(sub lambda) Depression by a Heat Current Along the lambda-Line

We report measurements of the depression of the superfluid transition temperature by a heat current (1 less than or = Q less than or = 100 microW/sq cm) along the lambda-line (SVP less than or = P less than or = 21.6 bar). At P = 21.6 bar, measurements were also performed in a reduced gravity (0.2g). Experimental results show that the pressure dependence of the depression and the gravity effect on the measurements are small, in qualitative agreement with theoretical predictions. Keywords: superfluid helium; Lambda transition; heat current

Liu, Yuanming↗
NASA NTRS1978

Overlapping emission peaks in the solar C I multiplets at lambda 1560 and lambda 1657

Observations of the C I multiplets at 1560 and 1657 A made with the University of Colorado spectrometer on the OSO 8 satellite are presented and compared with computed profiles for the Vernazza-Avrett-Loeser solar atmosphere. These are optically thick emission lines formed in the solar chromosphere that show the central reversals typical of such lines. In each multiplet there is an interesting case of overlapping emission peaks which shows that such peaks do not constructively combine but instead weaken. This behavior is easily understood and reproduced with an optically thick, non-LTE mode of formation for these lines and is not consistent with an optically thin mechanism. We also find that the shapes of these blends are very sensitive to the magnitude of the nonthermal microvelocities.

Shine, R. A.↗