Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “StarLight”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Research studies using OSO-6 zodiacal light experiment data

The results of research studies on the OSO-6 zodiacal light experiment, conducted during the period from May 1976 to October 1977 are described. A discussion is included of the instrument performance and the empirical calibrations developed. Main areas of the research performed, i.e., (1) zodiacal light variation analysis; (2) integrated starlight and diffuse galactic light; and (3) earth/moon libration region counterglow, are covered. Considerable data processing was performed during these studies and it is summarized. Recommendations for future research to complete the interim results are given.

Source record↗
NASA NTRS1978

Far-ultraviolet studies. III - A search for light scattered at large angles by dust

The Apollo 17 far-ultraviolet spectrometer was used during trans-earth coast to measure the brightness of two regions at moderate galactic latitudes. The signal obtained can be entirely accounted for by light from stars in the field of view, with no contribution from galactic-plane starlight scattered off interstellar dust. It is concluded that the interstellar grains are extremely poor large-angle scatterers in the far-ultraviolet.

Henry, R. C.↗
NASA NTRS1978

Spectrophotometry of Seyfert 2 galaxies and narrow-line radio galaxies

Results are reported for a spectrophotometric survey of several Seyfert 2 galaxies, intermediate Seyferts, and narrow-line radio galaxies. The emission-line spectra of the galaxies are analyzed, emphasizing line intensities, reddening, temperatures, densities, line strength correlations, line widths, and redshift differences. The continuous spectra are examined, and possible ionization sources are considered. It is found that: (1) there are no distinguishing differences between the spectra of Seyfert 2 galaxies and narrow-line radio galaxies; (2) the emission spectra are rich in lines from a wide range of ionization levels; (3) the continuum is starlight diluted by an underlying continuous spectrum; (4) the line widths of both classes of galaxies have the same distribution; (5) there appear to be regions of high and low ionization in the Seyfert 2 and narrow-line radio galaxies; (6) photoionization seems quite likely as the energy input to the gas; and (7) all the galaxies show a UV excess in their spectra.

Koski, A. T.↗
NASA NTRS1978

Far-infrared observations of Large Magellanic Cloud H II regions

Far-infrared emission has been measured from four Large Magellanic Cloud H II regions: the 30 Doradus nebula, MC75, MC76 and MC77. The far-infrared radiation is thermal emission from dust heated by starlight. The results show that the LMC H II regions, like H II regions in the Galaxy, have far-infrared luminosities comparable to the total luminosity of their exciting stars.

Werner, M. W.↗
NASA NTRS1978

Spin-related magnetism of interstellar grains

The magnetic dipole moments and internal magnetic fields due to the spin of electrically charged elongated nonmagnetic interstellar grains in kinetic equilibrium with their surroundings are computed for the grain-size range from 0.01 to 1.0 micron. It is shown that the induced magnetic moments and internal magnetic fields of charged spinning nonmagnetic grains of arbitrary composition and prolate spheroidal shape can be appreciable, possibly even exceeding 0.01 emu/cu cm for 0.01-micron grains. The results indicate that virtually all grains smaller than 0.1 micron in mean diameter, and all elongated grains smaller than about 1 micron in length, are immersed in local magnetic fields due to spin that are much larger than the ambient galactic field. Some implications of this effect are discussed in relation to the polarization of starlight by aligned dust grains and the primordial remanent magnetization found in primitive carbonaceous chondrites.

Srnka, L. J.↗
NASA NTRS1978

Discovery of polarized light scattered by dust around Alpha Orionis

Following the suggestion by Jura and Jacoby (1976), linearly polarized blue continuum starlight scattered by the dust shell around the M2 Iab star Alpha Orionis (Betelgeuse) has been discovered. The polarization has been traced in the NE, NW, SE, and SW directions and has positive (tangential) orientation. Some asymmetry of the optical depth in the shell exists 15 and 30 arcsec from the star. In the NE direction the polarization was measured as far as 90 arcsec (17,000 AU) from the star. The dependence of the average intensity of the scattered light from the nebula on angular distance from the star is more consistent with an inverse-square density law than with inverse 1.5 or inverse-cube laws. Assuming that the density is proportional to the inverse square of distance from the star, the scattering optical depth in blue light along a radius of 0.03 arcsec is no more than 0.15 + or - 0.05. Future observations of the wavelength dependence of polarization will allow a determination of grain size.

Mcmillan, R. S.↗
NASA NTRS1978

Spectrophotometry of the galaxies and nebulosity associated with the quasar III Zw 2

Results are presented for spectrophotometry of the object III Zw 2, the faint nebulosity to the NW of its nucleus, and two associated galaxies (a normal elliptical and a more luminous late-type spiral). The object III Zw 2 is defined to be a quasar on the basis of its dominant starlike nucleus, redshift, and optical and radio variability. The spectrophotometrically measured redshifts of the two associated galaxies are shown to place III Zw 2 as a member of Zwicky Cluster 0007.7+1056, thus establishing the cosmological origin of the quasar's emission-line redshift of 0.089. It is found that the nebulosity to the NW of the quasar exhibits an emission-line spectrum at the same redshift as the nucleus with an underlying red continuum, that the strength of the forbidden lines relative to the permitted lines is 3 to 4 times greater than in the nucleus, and that the data for the nebulosity are not well fitted by a bremsstrahlung emission spectrum, but are consistent with a spectrum of starlight from an underlying galaxy at the system redshift of 0.089.

Green, R. F.↗
NASA NTRS1979

Observations of the diffuse interstellar EUV radiation field

Results are reported for observations and a preliminary theoretical analysis of the diffuse interstellar EUV radiation field exhibiting positive measurable fluxes in the wavelength range from 912 to 1150 A. The observations were made with the UV spectrometers on the two Voyager spacecraft, and a spectral half-width of 30 A was obtained. The procedures used in the analysis are described in detail, particularly those relating to the elimination of thermal and cosmic-ray noise, internal instrumental scattering from bright lines, and possible contributions from direct starlight. Measurements in several directions reveal diffuse intensities at 975 A ranging from a maximum of about 10 to the -7th erg/sq cm per (sec sr A) near the galactic plane to an upper limit of 10 to the -8th erg/sq cm per (sec sr A). A comparison of the present measurements with various theoretical predictions and previous measurements indicates reasonable agreement with some theoretical predictions of the interstellar EUV intensity.

Sandel, B. R.↗
NASA NTRS1979

Some implications of revised OI /7990 A/ and OI /11287 A/ branching ratios

Recent laboratory, geophysical, and theoretical determinations of the O I (7990 A) and O I (11,287 A) branching ratios indicate that the generally used values based on the NBS transition parameters need revision. The O I (7990 A) branching ratio is about 300 times smaller than the NBS value, and the O I (11,287 A) is about one-quarter as large. The transitions are important in the generation of permitted atomic oxygen spectra in several types of astronomical source, including the Orion Nebula (M42), the Seyfert galaxy NGC 4151, Arcturus, and comets. The absence of the O I (7990 A) emission in M42 and NGC 4151 is consistent with its very small branching ratio, and previous conclusions based on its absence, such as the rejection of starlight excitation in the Seyfert galaxy, require reinvestigation. The reduction of the O I (11,287 A) branching ratio is pertinent to hydrogen L-beta fluorescence excitation of O I (1304 A) and O I (8446 A) emission and requires an upward revision of oxygen production rates in comets.

Christensen, A. B.↗
NASA NTRS1979

Astrophysical gamma-ray production by inverse Compton interactions of relativistic electrons

The inverse Compton scattering of background photon gases by relativistic electrons is a good candidate for the production of high-energy gamma rays in the diffuse interstellar medium as well as in discrete sources. By discussing the special case of the scattering of the diffuse starlight in the interstellar medium by cosmic ray electrons, we demonstrate that previous derivations of the gamma ray source function for this process on the basis of the Thomson limit of the Klein-Nishina cross section lead to incorrect values for gamma-ray energies above 100 MeV. It is shown that the Thomson limit is not applicable for the calculation of gamma-ray source functions in astrophysical circumstances in which target photons with energies greater than 1 eV are scattered by relativistic electrons.

Schlickeiser, R.↗
NASA NTRS1980

The Cosmic Background Explorer Satellite

The Cosmic Background Explorer (COBE) satellite, planned for launch in 1985, will measure the diffuse infrared and microwave radiation of the universe over the entire wavelength range from a few microns to 1.3 cm. It will include three instruments: a set of microwave isotropy radiometers at 23, 31, 53, and 90 GHz, an interferometer spectrometer from 1 to 100/cm, and a filter photometer from 1 to 300 microns. The COBE satellite is designed to reach the sensitivity limits set by foreground sources such as the interstellar and interplanetary dust, starlight, and galactic synchrotron radiation, so that a diffuse residual radiation may be interpreted unambiguously as extragalactic

Mather, J.↗
NASA NTRS1979

Interstellar polarization in an irregularly fluctuating medium

The interstellar polarization of starlight for an irregularly fluctuating medium is analyzed statistically. A general formulation is presented for the case in which the propagation distance s is larger than the coherence scale of the fluctuations. One specific result for randomly changing field direction is that the linear polarization saturates at a value which can be much less than unity, in agreement with observations.

Nee, S. F.↗
NASA NTRS1980

An optical emission-line phase of the extreme carbon star IRC +30219

Optical spectroscopic monitoring of the extreme carbon star IRC +30219 has revealed striking changes between 1977 and 1980. The stellar photosphere was barely visible in early 1979. There was an emission line spectrum consisting of H, forbidden O I, forbidden O II, forbidden N I, forbidden N II, forbidden S II, and He I. It is likely that these lines arose in a shocked region where recent stellar mass loss encountered the extensive circumstellar envelope. By late 1979, this emission-line spectrum had vanished, and the photosphere had reappeared. The weakening of the photospheric features in early 1979 was caused by increased attenuation of starlight and overlying thermal emission, both due to recently condensed hot dust grains.

Cohen, M.↗
NASA NTRS1980

Discovery of optical molecular emission from the bipolar nebula surrounding HD 44179

Spectrophotometry and spectropolarimetry with HD 44179 are presented. These measurements reveal that the very broad bump evident in previous low-resolution spectra possesses a large amount of structure, including groups of narrow emission lines and several diffuse features. A reduction in polarization, but constant position angle, through the bump indicates that this emission originates within the nebula itself and merely dilutes the polarized scattered starlight. A few very weak atomic emission lines are detected, but the overall feature, which strongly resembles the emission spectra of some molecules, remains unidentified. Constraints on the excitation mechanism are discussed.

Schmidt, G. D.↗
NASA NTRS1980

Galactic gamma rays produced by Compton scattering of cosmic ray electrons

Previous models of the Compton scattering of the galactic gamma rays have been based on starlight distributions determined from galactic mass models and a constant luminosity per unit mass. The fact that the spiral arms have a significantly higher photon density than does the base disk containing the bulk of the galactic mass has been neglected in calculating the Compton gamma-ray component. The inclusion of the spiral arm Compton component produces enhanced gamma-ray intensities along tangents to spiral arms. Irrespective of whether the cosmic-ray electron density is enhanced in the spiral arms, increased gamma-ray emission is produced along the spiral arm tangents due to increased photon density. Thus, cosmic ray sources are not necessarily located in the arms.

Higdon, J. C.↗
NASA NTRS1980

Galactic and extragalactic contributions to the far-ultraviolet background

Data from the 1350-1550 A bandpass channel of the 2.5-deg angular resolution extreme-ultraviolet telescope on the Apollo-Soyuz mission have been analyzed for stellar and airglow radiation contributions for the galactic latitude range above 30 deg. At intermediate latitudes, the resulting diffuse background is found to be correlated with the neutral hydrogen column density as determined by 21 cm radio data. This result, together with the observed anisotropy and mean intensity of the radiation field, is consistent with the hypothesis that scattering of galactic-plane starlight off dust grains having an albedo of 0.5 and a phase function coefficient of 0.5 is the primary source of the observed radiation field at the intermediate latitudes. The background intensity near the poles is, however, higher than expected from the H I column density and extinction measurements.

Paresce, F.↗
NASA NTRS1980

Brightness and polarization of the zodiacal light - Results of fixed-position observations from Skylab

A method is outlined for evaluating discrete and background starlight at the Skylab wavelengths so as to derive the total brightness of zodiacal light at five sky positions. These sky positions are north celestial pole, south ecliptic pole, vernal equinox and two places near the north galactic pole. Pioneer 10/11 imaging photopolarimeters were used to periodically measure sky brightness and polarization in the blue and red at heliocentric distances beyond 1.002 AU. Mean zodiacal light, which is assumed to be also solar color in total light, is then estimated by applying the method to all fixed-point observations.

Weinberg, J. L.↗
NASA NTRS1980

Planned observations of the diffuse sky radiation during shuttle mission STS-4

The planned space shuttle mission STS-4 will use the Skylab flight spare ten-color (near UV to near IR) photopolarimeter with boresighted 16 mm camera. This 164-hour mission will observe the zodiacal light to within approximately 20 deg of the sun (in and out of the ecliptic). The mission consists of several distinct phases: (1) tail-to-sun (TTS), belly to earth for 18 hours; (2) nose-to-sun, solar inertial for 79 hours; (3) bay-to-sun for 26 hours; and (4) passive thermal control for 37 hours. During the TTS phase, where most observations are scheduled, the instrument will scan back and forth in elevation at 4 deg/sec while the orbiter moves across the sky at its 4 deg/min orbital rate. The combined orbiter/instrument motion will result in a saw-tooth pattern of observations projected on the sky (between the 14 deg and 120 deg elevation limits) and will enable extensive measurements of the brightness, polarization and color of the background starlight to be made.

Weinberg, J. L.↗