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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Sound fields in a lined annular flow duct with lined radial splitters

High attenuation in the inlet duct of fan-jet engines is limited mainly because of two factors: the duct length is short and the frequency is high giving rise to a large duct width to wavelength ratio. Lined radial splitters may be installed. In this configuration not only is the absorbing surface area increased, the acoustic propagation properties in each of the segmented ducts are different to those in a cylindrical or annular duct without radial splitters. Such differences in properties can be used to advantage for mismatching the acoustic source. A lower order spinning mode must propagate as a higher order (integral or fractional) spinning mode. Cut-off phenomena may also be used to advantage. A theoretical modal analysis is made of the sound inside one segment of the annular duct with lined radial splitters.

Mungur, P.↗
NASA NTRS1993

New T Tauri stars in Chamaeleon I and Chamaeleon II

A new objective prism survey of the entire Chamaeleon I dark cloud and 2/3 of the Chamaeleon II cloud has uncovered 26 new H-alpha emission line objects that were missed by previous H-alpha plate surveys. The new H-alpha emission line objects have similar IR colors and spatial distributions to the known T Tauri stars in these dark clouds, and could represent the very low mass end of the stellar population in these clouds or an older, less active component to the usual classical T Tauri star population. The new H-alpha survey identified 70 percent of the total known Young Stellar Objects (YSOs) in Cha I, compared with 35 percent for IRAS, and 25 percent from the Einstein X-ray survey. Ten of the new objects are weak-lined stars, with H-alpha equivalent widths less than 10 A. Weak-lined T Tauri stars make up about half of the total population of young stars in the Chamaeleon I cloud, a proportion similar to the Taurus-Auriga cloud. Presented are coordinates, finding charts, and optical and IR photometry of the new emission-line objects.

Hartigan, Patrick↗
NASA NTRS1997

Implications of the broad Al-26 1809 keV line observed by GRIS

The astrophysical implications of the large width of the 1809 keV gamma ray line from the decay of radioactive Al-26, recently observed with the gamma ray imaging spectrometer (GRIS), are discussed. While there may be no apparent single mechanism that can explain the observed broadening, high speed dust grains, extremely hot superbubbles and a large, low density gaseous halo were identified in the Galactic center region as the possible origins. The implications of these observations on the hot gas content in the interstellar medium are discussed.

Chen, Wan↗
NASA NTRS1975

Transmissivity of carbon monoxide in the 2.3 microns band region

Line strengths and self and nitrogen broadened half-widths have been determined from high resolution spectroscopic measurements of selected lines in the 2.3 micrometer band region of CO. The CO 0-2 total band strength is estimated to be 2.086 + or - 0.146 cm/1 (ATM-cm)/1 STP which is higher than most previously reported values. The line half-widths are also generally higher than those in the literature.

Drayson, S. R.↗
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 NTRS1982

Evidence for high-altitude haze thickening on the dark side of Venus from 10-micron heterodyne spectroscopy of CO2

Infrared heterodyne spectroscopy provides data for isolated spectral lines with a spectral resolution which is small compared to the Doppler width. Heterodyne spectroscopy of CO2 lines near 10 micrometers was first reported for the atmosphere of Venus by Betz et al. (1976). The present investigation is concerned with observations of two absorption lines of (C-12)(O-16)2 conducted with an infrared heterodyne spectrometer interfaced with a solar telescope. The 10.8598-micrometer P(44) line was observed on the day side of Venus and the 10.3337-micrometer R(8) line was observed on the night side. It is shown that continuous opacity due to haze, and possible departures from vibrational LTE in CO2, are crucial considerations in fitting the observed lines.

Deming, D.↗
NASA NTRS1991

First results from Goddard High-Resolution Spectrograph - C I, S I, and CO toward Xi Persei and the physical conditions in diffuse clouds

Observations made by the Goddard High Resolution Spectrograph of the cool, neutral interstellar gas in the line of sight to Xi Per are reported. Heliocentric velocities and equivalent widths were measured for absorption lines of C I and S I. Synthetic spectra were computed and fitted to the observed CO(2-0) and (3-0) bands in the A IPi - X 1Sigma(+) system. Derived populations of the C I ground-state fine-structure levels and the CO ground-state rotational levels were used to derive densities of two of the three, and possibly four, detected cloud components. The velocity component displaying the strongest C I absorption reveals extraordinarily high pressure.

Smith, Andrew M.↗
NASA NTRS1999

AKN 564: An Unusual Component in the X-ray Spectra of NLSy1 Galaxies

We present an ASCA observation of the narrow-line Seyfert l (NLSyl) Arakelian 564. The X-ray light curve shows rapid variability, but no evidence for energy-dependence to these variations, within the 0.6 - 10 keV bandpass. A strong (EW approximately 70 eV) spectral feature is observed close to 1 keV. A similar feature has been observed in TON S180, another member of the NLSyl class of objects, but has not been observed in broad-line Seyfert galaxies. The feature energy suggests a large contribution from Fe L-shell lines but its intensity is difficult to explain in terms of emission and/or absorption from photoionized gas. The models which predict most emission at 1 keV are characterized by extreme values of column density, Fe abundance and ionization parameter. Models based on gas in thermal equilibrium with kT approximately l keV provide an alternative parameterization of the soft spectrum. The latter may be interpreted as the hot intercloud medium, undergoing rapid cooling and producing strong Fe L-shell recombination lines. In all cases the physical conditions are rather different from those observed in broad-line Seyferts. The hard X-ray spectrum shows a broad and asymmetric Fe K(alpha) line of large equivalent width (approximately 550 eV) suggestive of significant emission from the inner accretion disk. The profile can be explained by a neutral disk viewed at approximately 60 deg to the line-of-sight, contrary to the hypothesis that NLSyls are viewed pole-on. The large EW of this line, the strong 1 keV emission and the strong optical Fe emission lines all suggest an extreme Fe abundance in this and perhaps other NLSyls.

Turner, T. J.↗
NASA NTRS2007

The Suzaku Observation of the Nucleus of the Radio Loud Active Galaxy Centaurus A: Constraints on Abundances in the Accreting Material

A Suzaku observation of the nucleus of the radio-loud AGN Centaurus A in 2005 has yielded a broadband spectrum spanning 0.3 to 250 keV. The hard X-rays are fit by two power laws, absorbed by columns of 1.5 and 7 x 10(exp 23) per square centimeter. The dual power-laws are consistent with previous suggestions that the powerlaw components are X-ray emission from the sub-pc VLBI jet and from Bondi accretion at the core, or are consistent with a partial covering interpretation. The soft band is dominated by thermal emission from the diffuse plasma and is fit well by a two-temperature VAPEC model, plus a third power-law component to account for scattered nuclear emission, kpc-scale jet emission, and emission from X-ray Binaries and other point sources. Narrow fluorescent emission lines from Fe, Si, S, Ar, Ca and Ni are detected. The width of the Fe Ka line yields a 200 light-day lower limit on the distance from the black hole to the line-emitting gas. K-shell absorption edges due to Fe, Ca, and S are detected. Elemental abundances are constrained via the fluorescent lines strengths, absorption edge depths and the diffuse plasma emission lines. The high metallicity ([Fe/H]=+0.l) of the circumnuclear material compared to that in the metal-poor outer halo suggests that the accreting material could not have originated in the outer halo unless enrichment by local star formation has occurred. Relative abundances are consistent with enrichment from Type II and Ia supernovae.

Markowitz, A.↗
NASA NTRS1976

Observations of heavy-element recombination lines in the Rho Ophiuchi dark cloud at 13 centimeters wavelength

High-sensitivity observations at the carbon 140-alpha and 141-alpha recombination-line frequencies in the direction of the Rho Oph dust cloud show the presence of recombination lines of carbon and sulfur, but not of other heavy elements. These results require that the elements Si, Fe, and Mg are depleted by factors greater than 15, 10, and 2, respectively, most likely into interstellar grains, whereas sulfur is undepleted. They also require that only approximately one-sixth of the carbon is present in the gas phase in the cloud. From the observed size of the C II region together with the observed carbon depletion, it is inferred that the density in the carbon-line-emitting region is 25,000 per cu cm and that the size of the S II region is significantly larger than that of the C II region. The agreement between the widths of the recombination lines (which arise in a small region of the cloud) and those of the more widely distributed molecular species suggests that the lines in this cloud are broadened by microturbulence on a scale of much less than 0.1 pc.

Knapp, G. R.↗
NASA NTRS1975

Stark-broadening measurement and calculations for a singly ionized aluminum line

Using an electromagnetically driven shock tube and rapid scanning Fabry-Perot spectrometer, the Lorentzian half-width of the 4663-A line of singly ionized aluminum was measured and found to be 0.45 A plus or minus 20% for an environment corresponding to an electron density of 10 to the 17th power and an electron temperature of 18,500 K. Semiclassical and semiempirical calculations yielded values of 0.56 A and 0.41 A, respectively, while the distorted-wave approximation gave 0.51 A.

Allen, A. W.↗
NASA NTRS1981

Measurements of He D3 profiles in solar plages

Measurements of the profiles of the He D3 lines in solar plages are presented as a probe of the plage atmosphere. Observations were made at selected positions in quiescent plages during the period October 1978-April 1979 by the 25-cm coronagraph/3-m coude spectrograph at the Mees Solar Observatory on Mount Haleakala. Individual D3 plage profiles are fit well with a two-component, differentially moving atmosphere with constant source function and total Doppler width. The principal absorption is attributed to nearly stationary material, with a kinetic temperature less than 17,200 K, and velocity distribution is found to represent a net downflow in the plage atmosphere extending to around 12 km/sec. The present results for individual plage profiles are also noted to be consistent with those of Namba (1963). Time series of D3 profiles at fixed plage positions and the velocity spectra for nearby photospheric lines are observed to show general enhancements at periods of around 5 min, with redshift leading variations in line width by about 49 deg. Interpretations of the width variation as temperature variations are found not to be consistent with the properties of acoustic wave modes in a stratified atmosphere, presumably indicating magnetic field effects.

Landman, D. A.↗
NASA NTRS1977

A search for the H2 /3, 0/ S1 line in the spectrum of Titan

Results are reported for measurements of the quadrupole S1 line of the (3, 0) absorption band of H2 in spectra of Titan, which were performed at an effective resolution of 0.09 A by scanning with a PEPSIOS spectrometer over a range of 0.85 A centered at the expected position of the investigated line and sampling in 80 contiguous channels. No statistically significant H2 (3, 0) S1 feature is found in the spectra, but a three-sigma upper limit of 3 mA is set for the equivalent width of the S1 line that might be present in a co-added spectrum. It is concluded that these measurements do not provide any evidence for the presence of H2 in the atmosphere of Titan.

Muench, G.↗
NASA NTRS2007

The Suzaku Observation of NGC 3516: Complex Absorption and the Broad and Narrow Fe K Lines

We present results from a 150 ksec Suzaku observation of the Seyfert 1 NGC 3516 in October 2005. The source was in a relatively highly absorbed state. Our best-fit model is consistent with partial covering by a lowly-ionized absorber with a column density near 5x10(exp 22) cm(exp -2) and with a covering fraction 96-100 percent. Narrow K-shell absorption features due to He- and H-like Fe confirm the presence of a high-ionization absorbing component as well. A broad Fe K(alpha) diskline is required in all fits, even after the complex absorption is taken into account; an additional partial-covering component is an inadequate substitute for the continuum curvature associated with the broad line. The narrow Fe Ka line at 6.4 keV is resolved, yielding a velocity width commensurate with the optical Broad Line Region. The strength of the Compton reflection hump suggests a contribution mainly from the broad Fe line origin. We include in our model soft band emission lines from He- and H-like ions and radiative recombination lines, consistent with photo-ionization, though a small contribution from collisional ionization is possible.

Markowitz, Alex↗
NASA NTRS1974

Formation of the luminosity-sensitive O I multiplet at 7774 A

Line profiles and equivalent widths were calculated for the 7774 A multiplet of O I for model atmospheres in the effective temperature range 6000-6500 K for surface gravities in the range log g = 4.0-1.0. A kinetic equilibrium treatment of line formation can partially account for the observed luminosity sensitivity of these lines and considerably modifies the derived microturbulent broadening parameter. Line profiles obtained from kinetic equilibrium line-formation theory are much deeper than LTE profiles, and new observations of Canopus are presented to verify the essential correctness of this treatment.

Johnson, H. R.↗
NASA NTRS1986

Dual rectangular jets from a flat plate in a crossflow

Wind tunnel tests were carried out in order to study the single and dual rectangular crossflow jets injected from a flat plate perpendicular to a free stream. The length-to-width ratio of the jets was 3.97, and the spacing between the center lines was 4.7 times the width of a single jet. Surface pressure distributions were obtained for jet-to-freestream velocity ratios of 2.2 and 4, respectively. The following conclusions are offered on the basis of the experimental results: (1) the downstream extension of the negative pressures is extended to the dual jets in comparison to the single jet; (2) by increasing the jet-to-freestream velocity ratio the downstream extension of negative pressures is reduced, but negative upstream pressures become larger; (3) very high peak negative pressures occur at the front side edges of the rectangular jets compared to round jets. Velocity vector plots in the flowfield of the dual jets are given.

Kavsaoglu, M.↗