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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Optical studies of the Seyfert 2 X-ray galaxy NGC 2110

Spectrophotometry of the nucleus of the X-ray galaxy NGC2110 shows a typical Seyfert Type 2 spectrum with a strong galactic continuum. The widths of the forbidden lines are about 360 km/s (FWHM), H-beta being somewhat broader. The moderate Balmer decrement implies that the interstellar reddening is approximately 2.1 mag. The average electron density and temperature in the line-emitting region are approximately 300 per cu cm and 35,000 K, respectively. From measurements of the nebulium line, it is found that the extent of the nucleus measured along the major axis of the galaxy is about 10 arcsec (2100 pc) and the full range of gas velocities is about 700 km/s. A direct plate is discussed which shows faint spirallike features in NGC2110, a galaxy currently classified as elliptical. NGC2110 is a member of a new class (about 5 members) of very nearby (cz less than 2500 km/s) X-ray galaxies. Bradt et al. (1978) tentatively concluded that they are Seyfert Type 2 galaxies. This conclusion is supported, and it is shown that this is not inconsistent with the narrowness (less than 500 km/s FWHM) of their emission line.

Mcclintock, J. E.↗
NASA NTRS1983

Iron and magnesium in the white dwarf GD 40 - A test of diffusion theory

An outstanding problem in interpreting the properties of white-dwarf stars is related to the understanding of the chemical abundances in their atmospheres. The hydrogen-rich white-dwarf stars have monoelemental atmospheres, with small quantities of helium and no heavier elements observed in most, possibly all, stars with visible H lines. The helium-rich stars are more complex, and the existence of metallic lines in many of their spectra is now well confirmed. The DB star GD 40 (Gr 384) is the hottest He-rich white-dwarf star to show metal lines, apart from the extremely hot objects, such as HZ 21 and HD 149499B. The present investigation is concerned with IUE spectra which have been obtained of the GD 40. It is found that the near-UV is marked by strong Mg II lines along with broad blends of Fe II lines. An analysis is conducted of the abundances of Fe and Mg at the surface of GD 40 using a limited spectrum-synthesis technique with the measured equivalent widths of the best Fe II features.

Shipman, H. L.↗
NASA NTRS1984

Helium 10830 Angstrom Irradiance: 1975-1983

A fairly complete time series from late 1974 to mid-1983 is available of values of the equivalent width of the He I 10830A chromospheric spectrum line averaged over the visible solar disk. Variation from about 25 mA in 1975 to about 80 mA in late 1981 is the major component of the signal. The 10830 variation reaches minimum about a year before the sunspot minimum and reaches maximum about a year after sunspot maximum. Superposed on the solar cycle variation is a modulation of up to + or - 13 mAdu to the passage of active regions across the disk. Power spectral analysis of the time series shows a major peak at a synodic rotation period of 27.42 days and smaller peaks at 1/2, 1/4 and 1/6 of this period. The spectrum is well modeled by a basic fluctuating component with an exponentially decaying autocovariance function of scale time of 43 days. Analysis of the data indicates that the rotational modulation occurs in episodes that last from 4 to 10 rotations. These episodes arise when active regions tend to occur in a limited longitude range. The analysis also shows that the apparent rotation period increased from 1977 to 1981. The apparent rotation period since 1981 is markedly shorter.

Harvey, J. W.↗
NASA NTRS1987

Nine optically selected quasars with redshifts larger than 3

The detection of nine quasars with redshifts between 3.0 and 3.8 is reported. The quasars were all found in a grism survey from their Lyman-alpha emission line. The r magnitudes of the quasars range from 18.5 to 21.7. The strengths of the Lyman-alpha lines are comparable to the values observed in other quasars (rest equivalent widths from 40 to 160 A). The spectrum of one of the objects possesses complex broad absorption features, similar to those seen in PHL 5200. A preliminary evaluation of these findings suggests that the comoving quasar density declines gradually beyond z = 3.

Schmidt, Maarten↗
NASA NTRS1995

Ultraviolet to optical spectral distributions of northern star-forming galaxies

We report spectral energy distribution from the UV to the optical for a sample of 31 northern star-forming galaxies. We also present measurements for emission-line fluxes, continuum levels, and equivalent widths of absorption features for each individual spectrum as well as averages for the eight galactic activity classes, including normal, starburst, Seyfert 2, blue compact dwarf, blue compact, Low-Inonization Nuclear Emission Regions (LINER), H II, and combination LINER-H II galaxies.

Mcquade, Kerry↗
NASA NTRS1999

Relativistic Electrons Observed at UARS and the Interpretation of their Storm-Associated Intensity Variations

The High Energy Particle Spectrometer (HEPS) instrument on the Upper Atmosphere Research Satellite (UARS) provides a database of electron intensities well resolved in energy and pitch-angle. Because of its 57 deg. orbital inclination, UARS encounters with magnetic shells L greater than 2 occur quite far off-equator (B/B (sub 0) greater than 9), corresponding to equatorial pitch angle alpha (sub 0) greater than 20 deg. Data acquired by HEPS (October 1991 through September 1994) span the declining phase of Solar Cycle 22. To reveal the storm-associated time dependence of relativistic electron intensities over the wide range of energies (50 keV to 5 MeV) covered by HEPS, we divide the daily average of the measured spectrum at a given L value (bin width = 0.25) by the corresponding 500-day average and plot the results with a color scale that spans only 2.5 decades. The data show that our off-equatorial electron intensities typically increase with time after the end of recovery phase (not during main phase or recovery phase) of each geomagnetic storm. The delay in off-equatorial energetic electron response and the subsequent lifetime of the corresponding electron flux enhancement seem to increase with particle energy above 300 keV. The trend below 300 keV seems to be opposite, such that the delay varies inversely with electron energy. Our working hypothesis for interpretation is that stormtime radial transport tends to increase the phase-space densities of trapped relativistic electrons but typically leads to a flux increases at specified energies only as the current (as indicated by Dst) decays. Flux enhancements in early recovery phase are greatest for equatorially mirroring electrons, and to pitch-angle anisotropies are initially large. Subsequent pitch-angle diffusion broadens the flux enhancement to particles that mirror off equator, thus gradually increasing low-altitude electron intensities (as detected by HEPS/UARS) on time scales equal to about 20% of corresponding lifetimes against diffusion into the loss cone. Alternative interpretations will also be examined.

Pesnell, W. D.↗
NASA NTRS2002

Impact of MIE-Resonances on the Atmospheric Absorption of Water Clouds

Clouds strongly modulate radiative transfer processes in the Earth's atmosphere. Studies, which simulate bulk properties of clouds, such as absorption, require methods that accurately account for multiple scattering among individual cloud particles. Multiple scattering processes are well described by MIE-theory, if interacting particles have a spherical shape. This is a good assumption for water droplets. Thus, simulations for water clouds (especially for interactions with solar radiation) usually apply readily available MIE-codes. The presence of different drop-sizes, however, necessitates repetitive calculations for many sizes. The usual representation by a few sizes is likely to miss contributions from densely distributed, sharp resonances. Despite their usually narrow width, integrated over the entire size-spectrum of a cloud droplet distribution, the impact of missed resonances could add up. The consideration of these resonances tends to increase cloud extinction and cloud absorption. This mechanism for a larger (than by MIE-methods predicted) solar absorption has the potential to explain observational evidence of larger than predicted cloud absorption at solar wavelengths. The presentation will address the absorption impact of added resonances for typical properties of water clouds (e.g. drop size distributions, drop concentrations and cloud geometry). Special attention will be given to scenarios with observational evidence of law than simulated solar absorption; particularly if simultaneous measurements of cloud micro- and macrophysical properties are available.

Wiscombe, W.↗
NASA NTRS1985

New calorimetric all-particle energy spectrum

Both the maximum size N sub m and the sea level muon size N sub mu have been used separately to find the all-particle energy spectrum in the air shower domain. However the conversion required, whether from N sub m to E or from N sub mu to E, has customarily been carried out by means of calculations based on an assumed cascase model. It is shown here that by combining present data on N sub m and N sub mu spectra with data on: (1); the energy spectrum of air shower muons and (2) the average width of the electron profile, one can obtain empirical values of the N sub m to E and N sub mu to E conversion factors, and an empirical calorimetric all-particle spectrum, in the energy range 2 x 10 to the 6th power E 2 x 10 to the 9th power GeV.

Linsley, J.↗
NASA NTRS1976

The application of an optical Fourier spectrum analyzer on detecting defects in mass-produced satellite photographs

Various defects in mass-produced pictures transmitted to earth from a satellite are investigated. It is found that the following defects are readily detectable via Fourier spectrum analysis: (1) bit slip, (2) breakup causing loss of image, and (3) disabled track at the top of the imagery. The scratches made on the film during mass production, which are difficult to detect by visual observation, also show themselves readily in Fourier spectrum analysis. A relation is established between the number of scratches, their width and depth and the intensity of their Fourier spectra. Other defects that are found to be equally suitable for Fourier spectrum analysis or visual (image analysis) detection are synchronous loss without blurring of image, and density variation in gray scale. However, the Fourier spectrum analysis is found to be unsuitable for detection of such defects as pin holes, annotation error, synchronous loss with blurring of images, and missing image in the beginning of the work order. The design of an automated, real time system, which will reject defective films, is treated.

Athale, R.↗
NASA NTRS1973

The scattering mean free path in the Uranian atmosphere

New measurements of the equivalent widths of the 4.0 S(0) and S(1) H2 quadrupole lines in the Uranian spectrum have been obtained using high dispersion (4.12 A/mm) image-tube spectrography. The measured equivalent widths are 62 plus or minus 19 mA and 58 plus or minus 13 mA for the S(0) and S(1) lines, respectively. Curve-of-growth analysis in terms of a reflecting layer model yields an H2 column density of 780 (+940 or -330) km amagat and a temperature of 78 (+80 or -24) K. Interpretation using a semiinfinite, homogeneous, isotropically scattering model for line formation yields a scattering mean free path at 6400 A of 550 plus or minus 250 km amagat. Quoted errors for both the H2 column density and the scattering mean free path include the effect of uncertainty in the choice of atmospheric temperature. The results are discussed in terms of current models for the Uranian atmosphere.

Price, M. J.↗
NASA NTRS1983

Observation of an absorption feature in a gamma ray burst spectrum

A gamma ray burst was detected on March 25, 1978 by the High Energy X-ray and Low Energy Gamma Ray Experiment on HEAO-1. The burst spectrum shows an absorption feature at 55 + or - 5 keV with an equivalent width of 13 + or - 3 keV, values commensurate with those of similar features observed by the KONUS experiment. The burst spectrum also is characterized by a hard component extending from about 0.25-6 MeV. This component can be interpreted in terms of a fireball model for gamma ray bursts, which places the distance to the source at 1 kpc. The integrated fluence of the burst between 0.025 and 6 MeV is 1.5 x 10 to the -5th ergs/sq cm. The burst source has been localized to within a degree of RA = 237.5 deg and Dec = 76.2 deg.

Hueter, G. J.↗
NASA NTRS1976

The emission-line spectrum of a sunspot in the far-ultraviolet

The emission-line spectrum between 1200 and 1817 A from a sunspot in McMath region 12510 near the solar center is discussed. The spectrum was obtained by the normal-incidence spectrograph on Skylab. The principal results are: (1) the widths of emission lines originating in the chromosphere and lower transition region over the sunspot are much narrower than those previously reported for a polar coronal hole observed above the limb and a quiet chromospheric network observed near the solar center, indicating that the mass motions in the sunspot are less than in these other regions; (2) the sunspot spectrum, aside from the narrow widths of emission lines, is similar to spectra from the chromospheric network boundary. The intensities of lines in the sunspot are much enhanced relative to the network interior. From the full-width at half-maximum of the 1207-A Si III line, an optical depth at line center of 3.6 is deduced. Comparison with Parker's (1974) theory of sunspots shows that, if the enhancement of emission lines is due to enhanced transport of hydromagnetic waves generated in the sunspot convective zone, the mode of the waves is predominately Alfvenic.

Cheng, C.-C.↗
NASA NTRS1992

Hopkins ultraviolet telescope observations of the far-ultraviolet spectrum of NGC 4151

Observations of the FUV spectrum of the Seyfert galaxy NGC 4151 from 912 to 1860 A during the flight of Astro-1 aboard the space shuttle Columbia in December 1990 are reported. Broad emission lines with full-width at half-maximum of about 8500 km/s dominate the spectrum. Numerous absorption features modify the continuum shape, particularly at wavelengths shortward of Ly-alpha. The continuum turns over sharply below 1000 A and disappears by 924 A, well above the redshifted Lyman edge of NGC 4151 at 915 A. The absorption lines have intrinsic widths of about 1000 km/s and are blueshifted relative to the system velocity of NGC 4151 by 200-1300 km/s. Absorption of the continuum by the converging higher-order Lyman lines explains the sharp turnover of the continuum below 1000 A. The blueshifts of the absorption lines, their large intrinsic widths, and the inferred high densities are all consistent with outflowing material originating in the broad-line region.

Kriss, G. A.↗
NASA NTRS1969

The forbidden line

Ca II 7323 forbidden line in solar Fraunhofer spectrum, estimating center-limb variation of equivalent width of transition

Lambert, D. L.↗
NASA NTRS1973

A study of B 6 stars.

Because detailed information about the spectra of normal late B type stars is deficient, a study of the spectrum of zeta-Draconis, beta-Sextantis, and alpha-Leonis was undertaken to fill this lack and to provide data for comparison with observations of Bp stars, many of which are of late B spectral type. The study was made from high dispersion spectrograms which cover the spectral region 3100 to 6700 A, and from OAO-II spectral scans covering the spectral region 1100 to 3600 A. Profiles, equivalent widths, and central intensities of many lines in the spectrum of zeta-Draconis and of the major lines of beta-Sextantis are presented. The star alpha-Leonis rotates too rapidly for these measurements to be made from high resolution spectrograms. The star beta-Sextantis is the most massive and hottest of the three stars studied.

Underhill, A. B.↗
NASA NTRS1996

Electron-Impact-Induced Emission Cross Sections of Neon in the Extreme Ultraviolet

We have measured the extreme ultraviolet (EUV) spectrum of neon produced by electron excitation. The measurements were obtained under optically thin conditions, and at a spectral resolution of 0.5 nm full width at half maximum (FWHM). The most prominent features of the EUV spectrum between 45-80 nm are the resonance lines of Ne I at 73.6 and 74.4 nm and a multiplet of Ne II at 46.14 nm (the average value for the line center of the two closely spaced ion lines at 46.07 and 46.22 nm). Absolute emission cross sections of these lines at 300 eV were measured and compared to other previous measurements.

Neon extreme ultraviolet (EUV) spectrum EUV resona↗
NASA NTRS2010

Vacuum-Compatible Wideband White Light and Laser Combiner Source System

For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (<3.2 microradians). To meet this and other needs, the laser light from a single-mode fiber was combined, through a beam splitter window with special coating from broadband wavelengths, with light from multimode fiber. Both lights were coupled to a photonic crystal fiber (PCF). In many optical systems, simulating a point star with broadband spectrum with stability of microradians for white light interferometry is a challenge. In this case, the cameras use the white light interference to balance two optical paths, and to maintain close tracking. In order to coarse align the optical paths, a laser light is sent into the system to allow tracking of fringes because a narrow band laser has a great range of interference. The design requirements forced the innovators to use a new type of optical fiber, and to take a large amount of care in aligning the input sources. The testbed required better than 1% throughput, or enough output power on the lowest spectrum to be detectable by the CCD camera (6 nW at camera). The system needed to be vacuum-compatible and to have the capability for combining a visible laser light at any time for calibration purposes. The red laser is a commercially produced 635-nm laser 5-mW diode, and the white light source is a commercially produced tungsten halogen lamp that gives a broad spectrum of about 525 to 800 nm full width at half maximum (FWHM), with about 1.4 mW of power at 630 nm. A custom-made beam splitter window with special coating for broadband wavelengths is used with the white light input via a 50-mm multi-mode fiber. The large mode area PCF is an LMA-8 made by Crystal Fibre (core diameter of 8.5 mm, mode field diameter of 6 mm, and numerical aperture at 625 nm of 0.083). Any science interferometer that needs a tracking laser fringe to assist in alignment can use this system.

Azizi, Alineza↗
NASA NTRS1980

An absorption line in the ultraviolet spectrum of 40 Eridani B

Two excellent low-resolution spectra show an absorption line of equivalent width 3 A, near 1391 A, in the typical DA (hydrogen atmosphere) white dwarf 40 Eri B. The line is confirmed by a high-resolution spectrum and is the first seen in any DA star. Ultraviolet fluxes and the profile of Lyman-alpha confirm an effective temperature near 17,000 K. If the line is Si IV, it requires a temperature near 40,000 K. Unattractive possibilities are a hot circumstellar absorbing envelope dependent on accretion from companions, or formation at large optical depth in a transparent atmosphere with high Si/H. A suggestion that H2 should be considered leads to the possible interpretation as the (0, 5) transition of the Lyman band, formed at small optical depth. The band should be stronger in cooler DAs.

Greenstein, J. L.↗