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At least 1,099 records · Page 61
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NASA NTRS1987

Numerical models of star formation in X-ray cluster cooling flows

A grid of numerical models is used here to study how accretion flows are affected by star formation. The observables associated with these models are investigated, presenting their X-ray surface brightness profiles. An X-ray diagnostic is searched for that, in the absence of spatially resolved X-ray spectral data, can be an unambiguous indicator for ongoing star formation in cooling flows. The spatial distributions of newly formed stars are presented and compared to profiles of the accreting galaxy in each model. Whether the accretion population can form the luminous parts of the accreting galaxy or whether it forms a dark component is considered.

White, Raymond E., III↗
NASA NTRS1987

X-ray observations of the Ophiuchus, PKS 0745-191 and Cygnus-A clusters of galaxies

Observations are reported of the X-ray emission from three bright clusters of galaxies at low Galactic latitudes: the Ophiuchus, PKS 0745-191, and Cygnus-A clusters. Temperatures and iron abundances are determined from Exosat spectral data. Images of the Ophiuchus cluster show it to have a high central density and a cooling flow. Measurements of a high gas density around PKS 0745-191 and are confirmed, and it is shown that the X-ray emission is centered on the radio galaxy. The PKS 0745-191 cluster is the most distant object for which an abundance has been measured from X-ray spectra. The spectrum of Cygnus-A contains a highly absorbed power-law component that is identified with the nucleus of the radio source.

Arnaud, K. A.↗
NASA NTRS1987

The quality of geological information derivable from high resolution reflectance spectra - Results for mafic silicates

High-resolution visible and near-infrared diffuse reflectance spectra of mafic silicates can be deconvolved to yield quantitative information concerning mineral mixture properties, and the results can be directly applied to remotely sensed data. Spectral reflectance measurements of laboratory mixtures of olivine, orthophyroxene, and clinopyroxene with known chemistries, phase abundances, and particle size distributions have been utilized to develop correlations between spectral properties and the physicochemical parameters of the samples. A large number of mafic silicate spectra were measured and examined for systematic variations in spectral properties as a function of chemistry, phase abundance, and particle size. Three classes of spectral parameters (ratioed, absolute, and wavelength) were examined for any correlations. Each class is sensitive to particular mafic silicate properties. Spectral deconvolution techniques have been developed for quantifying, with varying degrees of accuracy, the assemblage properties (chemistry, phase abundance, and particle size).

Cloutis, E. A.↗
NASA NTRS1987

CO2 DIAL measurements of water vapor

CO2 lidars have heretofore been used to measure water vapor concentrations primarily using the 10R(20) line at 10.247 microns, which has a strong overlap with a water vapor absorption line. This paper discusses the use of that line as well as other CO2 laser lines for which the absorption coefficients are weaker. The literature on measurement of water vapor absorption coefficients using CO2 lasers is reviewed, and the results from four laboratories are shown to be generally consistent with each other after they are normalized to the same partial pressure, temperature, and ethylene absorption coefficent for the 10P(14) CO2 laser line; however, the agreement with the Air Force Geophysics Laboratory's HITRAN and FASCOD 2 spectral data tapes is not good either for the water vapor absorption lines or for the water vapor continuum. Demonstration measurements of atmospheric water vapor have been conducted using the Mobile Atmospheric Pollutant Mapping System, a dual CO2 lidar system using heterodyne detection. Results are discussed for measurements using three sets of laser line pairs covering a wide range of water vapor partial pressures.

Grant, William B.↗
NASA NTRS1987

The Portable Instant Display and Analysis Spectrometer (PIDAS)

A field spectrometer covering the range 0.4 to 2.5 microns was developed that acquires spectra in 2 seconds at 872 points within the spectrum. The Portable Instant Display and Analysis Spectrometer (PIDAS) can acquire spectra every 8 seconds and stores up to 288 spectra in bubble memory. A hand held display unit allows for display of the current spectrum acquired and superimposed on one of 128 permanently stored library spectra. PIDAS represents a major advance in the technology of field spectral data acquisition and for the first time makes possible the acquisition of enough spectra to characterize the mean and intraclass variance within a LANDSAT MSS or TM pixel.

Goetz, Alexander F. H.↗
NASA NTRS1987

The large-scale radio structure of R Aquarii

Radio continuum observations of the R Aqr symbiotic star system, using the compact D configuration of the VLA at 6-cm wavelength, reveal a large-scale about 2-arcmin structure engulfing the binary, which has long been known to have a similar optical nebula. This optical/radio nebula possesses about 4 x 10 to the 42nd ergs of kinetic energy which is typical of a recurrent nova outburst. Moreover, a cluster of a dozen additional 6-cm radio sources were observed in proximity to R Aqr, most of these discrete sources lie about 3 arcmin south and/or west of R Aqr and, coupled with previous 20-cm data, spectral indices limits suggest a thermal nature for some of these sources. If the thermal members of the cluster are associated with R Aqr, it may indicate a prehistoric eruption of the system's suspected recurrent nova. The nonthermal cluster members may be extragalactic background radio sources.

Hollis, J. M.↗
NASA NTRS1988

An X-ray perspective on quasar continua

Two of the major continuum features seen in normal quasars are discussed on the basis of new Einstein IPC spectral data. Particular attention is given to the possibility of a single IR-to-X-ray 'baseline' power law and to the connection between radio-loudness and the presence or absence of a turn-up in the X-ray spectrum toward higher energies. It is found that radio-loud quasars have systematically flatter X-ray spectra than do radio-quiet quasars in the present Einstein IPC survey which may be due to a mix of two components. These are a radio-associated component with a flat slope and an optical-associated component with a steeper slope.

Elvis, Martin↗
NASA NTRS1988

Quasar ionization of Lyman-alpha clouds - The proximity effect, a probe of the ultraviolet background at high redshift

The distribution of lines in the Ly-alpha forests in quasar spectra is examined using spectral data from 19 quasars with emission lines redshifts z sub Q ranging from 1.7 to 3.8. The number density of Ly-alpha lines generally increases with resdhift z, but there exists a countervailing trend of diminishing number density within individual quasar spectra as z tends to z sub Q. Evidence is presented that this countervailing trend is due to enhanced ionization of Ly-alpha clouds by the bright nearby quasars in whose spectra they are observed. It is suggested that this proximity effect should be used as a powerful tool to measure locally the ionizing flux emitted by high-redshift objects.

Bajtlik, Stanislaw↗
NASA NTRS1988

Mass loss in a B2 IIIe star - Omega Orionis 1978-1984

A combination of long-term optical polarimetric, photometric, spectrometric, and UV spectral data has confirmed that all the observed portions of Omega Ori's outer atmosphere are variable on a variety of time scales. The shortest confirmed variations are detectable over a few hours, and the longest changes are observed on time scales of years. A straightforward interpretation of the available data is that the continuum polarization, continuum-magnitude changes, and color changes produced are in a presumably equatorial disk close to the stellar photosphere.

Sonneborn, George↗
NASA NTRS1987

An orthogonal decomposition of the axisymmetric jet mixing layer utilizing cross-wire velocity measurements

The structure of the mixing layer of the axisymmetric turbulent jet was investigated using cross-wire velocity measurements, which generated radial and streamwise cross-spectral data at eight radial positions and 25 azimuthal positions. The results show the existence of an azimuthal coherent ringlike structure dominated by axisymmetric mode near the potential core; however, from the center of the mixing layer out toward its low-speed side, the fourth, fifth, and sixth modes are dominating. A mechanism for the life cycle of coherent structures and for turbulence production in the axisymmetric jet mixing layer is proposed, which accounts for the observed phenomena and is amenable to dynamical analysis using the equations of motion.

Glauser, Mark N.↗
NASA NTRS1988

Measurements of several atmospheric gases above the South Pole in December 1986 from high-resolution 3- to 4-micron solar spectra

This paper reports the quantitative analysis of absorption features of a number of atmospheric gases in 0.02/cm resolution 3- to 4-micron solar spectra recorded at the Amundsen-Scott South Pole Station. The measurements were obtained shortly after the austral spring ozone minimum and define, for the first time, the ambient levels of the species immediately following the breakup of the polar vortex. The retrieved total vertical column amounts in molecules per sq cm are: 2.4 + or - 0.4 x 10 to the 21st for H2(O-16), 4.5 + or - 0.5 x 10 to the 18th for H2(O-18), 3.9 + or - 0.4 x 10 to the 17th for HDO, 2.1 + or - 0.2 x 10 to the 19th for CH4, 5.1 + or - 0.5 x 10 to the 21st for CO2, 3.9 + or - 0.4 x 10 to the 18th for N2O, and 3.7 + or - 0.5 x 10 to the 15th for C2H6. Identification of (C-12)H3D absorption features and a search for H2CO absorption in the spectral data are also described.

Goldman, Aaron↗
NASA NTRS1988

The nature of S Andromedae (SN 1885A)

The spectral data on S Andromedae, or SN 1885A, which indicate that it was a type I supernova, are reexamined, and it is concluded that SN 1885A belongs to a supernova class distinct from types SN Ia and SN Ib. The light curve had a rapid rise to maximum, a rapid postmaximum decline, and a large magnitude difference between maximum and 150 days postmaximum, compared to other type I events. SN 1885A was probably a low-mass explosion, ejecting 0.1-0.3 solar mass of matter mostly in the form of Ni-56. This suggests that it left behind a compact remnant, either a neutron star or a white dwarf.

Chevalier, Roger A.↗
NASA NTRS1988

Surface compositional and structural aspects of Martian samples

There are many excellent reasons to examine the surface composition of a wide range of Martian samples. The existing spectral data indicate that many dust and soil particles have a thin Fe(+3) layer with a typical particle size in the 10 micrometer to 400 micrometer range. In view of the high CO2 content of the atmosphere, one might expect that surface carbonates should be present. In addition to chemisorbed material there will probably exist physisorbed atmospheric components of the atmosphere including oxygen, nitrogen and water vapor. The latter could possibly give rise to some hydrated minerals. Using ultra-high-vacuum/mass spectrographic techniques it should be possible to detect physisorbed and moderately strong chemisorbed species on the particle surfaces with a temperature programmed degassing procedure. In some instances such an approach is capable of helping distinguish between volcanic and impact generated materials by detecting the presence of fumerolic gases. Such gases typically condense on the exterior of the ejected particles. Additionally surface atomic and chemical compositions should be examined by a combination of modern surface analytical techniques. The combination we currently have in Buffalo at SUNY would appear to be one of the best available including ESCA (150 micrometer spot capability) Auger (SAM) with 300 A focussing for surface compositional surveys, SIMS for high sensitivity trace element detection and ISS for immediate surface layer analysis.

Cadenhead, D. A.↗
NASA NTRS1989

Line mixing effects in solar occultation spectra of the lower stratosphere - Measurements and comparisons with calculations for the 1932/cm CO2 Q branch

Line mixing effects have been observed in a CO2 Q branch recorded in 0.01/cm-resolution IR solar occultation spectra of the lower stratosphere. The spectral data were obtained by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during the Spacelab 3 mission in the spring of 1985. Analysis of the 1932.47/cm Q branch of (C-12)(O-16)2 shows absorption coefficients below the band origin about 0.62 times those calculated using a standard Voigt line-shape function. Calculations of line mixing using the Lorentz halfwidths of the lines and a simple energy-gap scaling law to parameterize rotational energy transfer reproduce the observed absorption coefficients to about 10 percent. The present results provide the first quantitative information on air-broadened line mixing effects in a Q branch at low temperatures (about 210 K) and show that these effects are significant even at the low pressures of the lower stratosphere (about 100 mbar).

Rinsland, Curtis P.↗
NASA NTRS1989

The absolute solar soft X ray flux in the 20- to 100-A region

Solar spectral data are used together with absolute neon ionization cell data to estimate the absolute solar soft X-ray flux and its variation with solar activity in the 20- to 100-A region. The dependence of the integrated solar soft X-ray flux between 20 and 100 A on the daily 10.7 cm radio flux observed at 1 AU is determined. An estimate is obtained of the maximum flux that can be expected over the solar cycle.

Feng, W.↗
NASA NTRS1989

The thermal structure of Triton's atmosphere - Pre-Voyager models

Spectral data from earth observations have indicated the presence of N2 and CH4 on Triton. This paper outlines the use of the 1-D radiative-convective model developed for Titan to calculate the current pressure of N2 and CH4 on Triton. The production of haze material is obtained by scaling down from the Titan value. Results and predictions for the Voyager Triton encounter are as follows: A N2-CH4 atmosphere on Triton is thermodynamically self consistent and would have a surface pressure of approximately 50 millibar; due to the chemically produced haze, Triton has a hot atmosphere with a temperature of approximately 130 K; Triton's troposphere is a region of saturation of the major constituent of the atmosphere, N2.

Mckay, Christopher P.↗
NASA NTRS1989

Implementation issues in source coding

An edge preserving image coding scheme which can be operated in both a lossy and a lossless manner was developed. The technique is an extension of the lossless encoding algorithm developed for the Mars observer spectral data. It can also be viewed as a modification of the DPCM algorithm. A packet video simulator was also developed from an existing modified packet network simulator. The coding scheme for this system is a modification of the mixture block coding (MBC) scheme described in the last report. Coding algorithms for packet video were also investigated.

Sayood, Khalid↗
NASA NTRS1989

Ecological study of peat landforms in Canada and Alaska

Over 20 percent of the land surface of Canada and Alaska is covered by peatlands, which may be defined as any waterlogged ecosystem with a minimum thickness of 20 cm of organic matter in the soil. Past investigations have demonstrated the value of aerial photographs in identifying the major vegetation types and analyzing the biotic and hydrogeologic processes that control the development of these peatlands. In the present study, LANDSAT TM imagery was used in conjunction with field studies to determine the utility of this satellite sensor for detecting these important processes. Although the vegetation landforms within these major peat basins are visible on aerial photographs, LANDSAT TM imagery provides essential new evidence for their analysis. Spectral data from the LANDSAT TM system provides: (1) synoptic views of the patterns across large portions of these peat basins, indicating important physiographic controls on peatland development, (2) more sensitive detection of the major vegetation types, allowing rapid quantitative estimates to be made of their distribution and aerial extent, (3) discrimination of bog areas with potentially rapid or slow rates of peat accumulation, (4) identification of discharge zones for groundwater, which apparently represents the most important source of alkalinity in these peat basins, and (5) detection of flow patterns in water tracks that appear nearly uniform on standard aerial photographs.

Glaser, Paul H.↗