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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 631 records · Page 35
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NASA NTRS1981

UV chromospheric and circumstellar diagnostic features among F supergiant stars

A survey of F supergiant stars to evaluate the extension of chromospheric and circumstellar characteristics commonly observed in the slightly cooler G, K, and M supergiant is discussed. An ultraviolet survey was elected since UV features of Mg II and Fe II might persist in revealing outer atmosphere phenomena even among F supergiants. The encompassed spectral types F0 to G0, and luminosity classes Ib, Ia, and Ia-0. In addition, the usefulness of the emission line width-to-luminosity correlation for the G-M stars in both the Ca II and Mg II lines is examined.

Stencel, R. E.↗
NASA NTRS1981

The UV variability of the Seyfert 1: Galaxies 3 Zw 2 and Markarian 509

The two galaxies differ markedly in their radio properties. III Zw 2 is a strong source with a highly variable compact component while MK 509 is a very weak source. Both galaxies show significant variations in X-rays and MK 509 has shown variations at optical wavelengths as well. Simultaneous observations were made in the ultraviolet, optical and infrared in order to examine three fundamental aspects of the origin of the continuum emission: are these thermal and nonthermal components; how large is the emitting region; and does the UV flux originate in the same region responsible for the optical, IR, radio and/or X-ray continuum emission?

Huchra, J.↗
NASA NTRS1981

Development of silane-hydrolysate binder for UV-resistant thermal control coatings

Detailed characterizaton and formulation studies were performed on a methyltriakoxysilane hydrolysate as a binder for thermal control coatings. The binder was optimized by varying hydrolysis temperature, time, catalyst type, and water concentration. The candidate coating formulations, based on this binder with TiO2 pigment, were optimized via a detailed series of sprayed test panels that included the parameters of binder/pigment ratio, ethanol content, pigment particle size, coating thickness and cure conditions. A typical optimized coating was prepared by acetic acid catalyzed hydrolysis of methyltriethoxysilane with 3.25 mol-equivalents of water over a 24 hour period at room temperature. The resulting hydrolysate was directly mixed with pre-milled TiO2 (12 grams pigment/26 grams binder) to yield a sprayable consistency. Panels were sprayed to result in a nominal cure coating thickness of 2 mils. Cure was affected by air drying for 24 hr at room temperature plus 72 hr at 150 F. These coatings are typically extremely tough and abrasion-resistant, with an absorptance (alpha) of 0.20 and emittance (e) of 0.89. No significant coating damage was observed in the mandrel bend test, even after exposure to thermal cycling from -160 to 160 F. Vacuum exposure of the coatings for 930 hours at 1 equivalent UV sun resulted in no visible degradation and no significant increase in absorptance.

Patterson, W. J.↗
NASA NTRS1980

The diffuse UV background

The diffuse radiation field in the UV (900-3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure and evolution. The redshifted emission from an intergalactic medium may be observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn-Peterson test.

Paresce, F.↗
NASA NTRS1981

Ozone profiling from backscattered UV radiance measurements A new procedure

This paper presents a data analysis technique that has been developed to support a stratospheric ozone measurement and profiling program. The data consist of solar backscattered UV radiation monitored by a spacecraft. The output consists of ozone mixing ratio profiles complete with error bars throughout the atmosphere. The technique is based upon principles of nonlinear optimal estimation. It provides a number of desirable features that have not been available together in any previously constructed technique for the problem. Iteration on both radiation measurements and total ozone measurements is among these features.

Whitney, C. K.↗
NASA NTRS1981

Determination of solar proton fluxes and energies at high solar latitudes by UV radiation measurements

The latitudinal variation of the solar proton flux and energy causes a density increase at high solar latitudes of the neutral gas penetrating the heliosphere. Measurements of the neutral density by UV resonance radiation observations from interplanetary spacecraft thus permit deductions on the dependence of the solar proton flux on heliographic latitude. Using both the results of Mariner 10 measurements and of other off-ecliptic solar wind observations, the values of the solar proton fluxes and energies at polar heliographic latitudes are determined for several cases of interest. The Mariner 10 analysis, together with IPS results, indicate a significant decrease of the solar proton flux at polar latitudes.

Witt, N.↗
NASA NTRS1981

Evidence for sulphur implantation in Europa's UV absorption band

The UV spectral characteristics of the Galilean satellites are investigated (using data from the International Ultraviolet Explorer (IUE) spacecraft) as a function of the orbital position, large-scale areal variability, and temporal dynamics. The discovery of an absorption feature at 280 nm in Europa's reflection spectrum is reported and observations show that the absorption is strongest on the trailing hemisphere (central longitude 270 degrees). The feature resembles SO2 and seems to result from S-O bond formation between deeply implanted sulphur atoms and the adjacent damaged water-ice-lattice. The sulphur supposedly comes from energetic (hundreds of keV) sulphur ions that are present in the Jovian magnetosphere. An appropriate equilibrium condition can be found to match the observed spectral data if sputtering erosion occurs at no greater than approximately 20 meters per one billion years.

Lane, A. L.↗
NASA NTRS1982

Suggested UV spectral classification criteria for A stars

Criteria for determining effective temperature and electron density independently of abundances, for A, late B, and F stars are given. Comparison of IUE data with standard classification techniques, shows that for late B and A stars, temperature classification by UV spectra is more sensitive than classification using visual spectra. The long wavelength wing of the Lyman is recommended for these stars. For A and F stars, the ratio of the Mg (2580 A) and Mg+ (2800A) resonance lines gives a good temperature/electron density (ne) criterion which is nearly independent of metal abundance (Z). The SiI discontinuities give an excellent temperature classification for A and F stars, but it is dependent on Z and ne. If the absolute intensities of either of the Mg lines are added to the criteria, three classification criteria for a three dimensional classification, according to temperature, ne and Z, are obtained.

Boehm-Vitense, E.↗
NASA NTRS1982

X-ray and UV spectra of two quasars: PKS0637-75 and PKS1004+13 (4C13.41)

Two quasars, 4C13.41 (1004+13, V approx. 15.2, z = 0.140) and PKS0637-75 (V = 15.75, z = 0.651) were observed in December 1980 with IUE. Both were detected in the short wavelength region. 4C13.41 has the lowest X-ray luminosity/optical luminosity measured in quasars. PKS0637-75 was observed quasi-simultaneously with the Einstein Observatory and a spectrum obtained with the IPC. The UV and soft X-ray spectra have been combined and are discussed together with the optical and infrared data for both objects.

Elvis, M.↗
NASA NTRS1982

UV emission from he M1 supergiant TV Gem

Low and high dispersion ultraviolet spectra were obtained of the M1 supergiant TV Gem with IUE. Previous IUE observations of this late type supergiant revealed unexpected UV continuum emission, perhaps arising from an early B companion. Low resolution spectra obtained approximately one year apart suggest that the strong Si III in combination perhaps with O I at wavelengths approximately 1300 A varies considerably with time. Large variation in the column density is required to explain these changes. Sporadic mass expulsion with mass loss rates dM/dt approximately 0.00001 solar mass yr minus 1st power from the M supergiant could lead to a dense circumstellar wind near the hot early companion, and thus could account for these observed variations in equivalent width. The high resolution spectrum in the 2000 to 3200 A wavelength range is characterized by narrow absorption lines primarily due to Fe II, Mn II and Mg II (h and k), which are skewed in profile with an extended red wing. This profile structure is tentatively attributed to interstellar absorption and an intervening differentially moving cloud in the direction of Gem OB1, of which TV Gem is a known association member.

Michalitsianos, A. G.↗
NASA NTRS1982

UV observations of the 1981 eclipse of 32 Cygni

Preliminary results of an extensive set of high dispersion UV spectra of the supergiant eclipsing system 32 Cyg are detailed and contrasted with spectroscopic studies of other Zeta Aur systems.

Stencel, R. E.↗
NASA NTRS1981

Far-UV, visible, and near-IR reflectance spectra of frosts of H2O, CO2, NH3 and SO2

Measurements in the 0.1-2.5 micron range are presented for the reflectance spectra of the frosts of several volatiles pertinent to the study of comet nuclei. The frost spectra have distinctive features permitting their identification by spectroscopic reflectance remote sensing, notably in the far UV. It is found that: (1) H2O has a minimum at 0.16 microns and a maximum at 0.13 microns; (2) CO2 has minima near 0.21, 0.18 and 0.125 microns, with maxima at 0.19, 0.135 and 0.120 microns; (3) NH3 is bright at wavelengths longer than 0.21 microns, where reflectance drops to a value of only a few per cent at shorter wavelengths; (4) SO2 has a sharp drop at 0.32 microns, with a minimum at 0.18 microns and a maximum at 0.13 microns. The features in the frost spectra largely correspond to absorption line bands in the gas phase.

Hapke, B.↗
NASA NTRS1982

Vacuum deposition of iridium on large astronomical mirrors for use in the far UV

An iridium coating has been deposited by electron-beam evaporation on a 0.91-m mirror which serves as the telescope primary of a sounding rocket instrument for far-UV spectrometry. The evaporation was carried out by applying 8 kV at 400 mA to the electron gun. Zone refined Ir of 99.99% purity was used, and the electron beam was electromagnetically swept over the surface of the evaporant. Under these conditions, deposition rates of 0.55 A/sec were achieved. The reflectance distribution achieved at a wavelength of 584 A was extremely uniform; the mean reflectance was 21.2% with a standard deviation of only 0.3%. This represents a substantial improvement over Al + MgF2 and Al + LiF coatings for applications involving multiple reflections and weak signals, as might be expected in a high-resolution spectrograph studying distant celestial objects.

Herzig, H.↗
NASA NTRS1982

Organic and inorganic interpretations of the Martian UV-IR reflectance spectrum

Viking Lander biology experiment gas chromatography-mass spectrometer analysis has detected no organic molecules above a concentration of parts per billion. The questions considered here include the reason for the lack of organic molecules at the landing sites, whether the sterility of the two sites is representative of the whole of Mars, and whether there may be locations more conducive to organic compound formation and preservation. After simulating the destruction of organic compounds in Mars-like laboratory conditions and examining whether the destructive mechanism might obtain throughout the planet, UV and IR reflectance spectra are re-examined for any evidence of organic molecules and an upper limit is determined for organic carbon content of average Martian soil. It is found that the average Martian soil is poor in inorganics, presents a poor habitat for carbon chemistry-based life forms, and is not likely to preferentially preserve such organisms anywhere on the planet.

Pang, K. D.↗
NASA NTRS1981

Lanning 10 and 33 - The X-ray, UV, and optical fluxes

UV spectra from IUE, optical spectroscopy, broad band photometry, and upper limits on the X-ray flux from Einstein are used to specify the characteristics of Lanning 10 and 33. Data on Lanning 33 are consistent with a 22,000 K Be star at a distance of 5 to 7 kpc, and Lanning 10 appears to include a F5-G0 star plus a hot component greater than 35,000 K at a distance of 0.9 to 1.3 kpc. The optical eclipsed fluxes are subtracted from the uneclipsed, and the observed fluxed distribution of the eclipsed light does not follow a simple power law, but is closer to a 12,000 K + or - 1000 K blackbody. Lanning 10 is placed in the category of VY Scl variables.

Szkody, P.↗
NASA NTRS1982

A new look at the ionosphere of Jupiter in light of the UVS occultation results

Neutral model atmospheres derived from the Voyager UV Spectrometer's solar and stellar occultation data are used to calculate Jupiter ionospheric electron density profiles, demonstrating the inadequacy of such methods. It is also shown that electron densities calculated by means of standard parameters are larger than those measured by both Pioneer and Voyager. McElroy's (1973) suggestion as to the importance of H2 vibrational excitation is investigated, and it is found that no single vibrational temperature is appropriate for the entire thermosphere. The long recombination time constants involved in the plasma's movement, due to either meridional winds or electric fields, through large vertical distances, is shown to account for the observed electron density profiles. It is suggested that the outflow, and possibly the inflow, of plasma may play a role in the definition of electron density profiles.

Mcconnell, J. C.↗
NASA NTRS1982

X-ray and UV radiation from accreting nonmagnetic degenerate dwarfs. II

Numerical calculations of X-ray and UV emission from accreting nonmagnetic degenerate dwarfs are reported, which span the entire range of accretion rates and stellar masses. Calculations include the effects of bremsstrahlung, Compton cooling, radiation pressure, albedo of the stellar surface, Compton degradation and free-free abscription of the X-ray spectrum by the accreting matter. Maximum X-ray luminosity for degenerate dwarfs undergoing spherical accretion is found to be 2.2 x 10 to the 36th ergs/s, which is little changed if accretion occurs radially over only a fraction of the stellar surface, so that the emitted radiation escapes without significant scattering. The temperature characterizing the X-ray spectra produced by degenerate dwarfs strongly depends on the stellar mass and the accretion rate, and it is suggested that the correlation between spectral temperature and luminosity is an important signature of degenerate X-ray sources.

Kylafis, N. D.↗
NASA NTRS1981

Study of the response of stratospheric ozone to perturbations in the solar constant and solar UV flux

A one-dimensional radiative-convective photochemical model has been used to examine the response of stratospheric and total ozone to perturbations in the solar flux. The model considers a detailed chemical reaction mechanism; vertical transport is parameterized through eddy diffusion coefficients. The temperature profile is calculated using a radiative transfer model for both time-dependent and steady-state cases. Results are discussed for the following types of perturbations: a 5% increase in the solar UV flux in the wavelength range 175-300 nm, a 5% increase in the solar constant, and an annual 6.6% variation in the solar constant associated with the variation in the earth-sun distance.

Natarajan, M.↗