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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Observations of Uranus, Neptune, and Titan by the International Ultraviolet Explorer

The ultraviolet spectra of Uranus, Neptune, and Titan do not reveal absorption features at 7-A resolution from 2100 to 3200 A. Upper limits of from 1 to 3 A are set for the equivalent widths of narrow absorptions, which corresponds to a CO/H2 mixing ratio less than 2 x 10 to the -4th in the case of Uranus. The slopes of the continuum reflectivities of Uranus and Neptune are consistent with the semi-infinite Rayleigh-Raman scattering model of Cochran, while the absolute levels are matched only if solar photometry is modified within acceptable limits. An alternative, but less satisfactory explanation of the new data is that the UV reflectivities of both Uranus and Neptune are depressed uniformly by a continuum absorber. The suggestion by Savage et al (1980) that the albedo of Uranus decreases by approximately 20% from 2200 to 1800 A is not confirmed. For Titan, the albedo decreases monotonically toward shorter wavelengths down to 2300 A. New limits are set for the pressure level in the atmosphere of Titan up to which the real, but presently unidentified, UV absorber there must extend, and for the fraction of Titan that must be covered by this absorber

Caldwell, J.↗
NASA NTRS1981

High sensitivity operation of discrete solid state detectors of 4 K

Techniques are described to allow operation of discrete solid state detectors at 4 K with optimized junction field effect transistor (JFET) amplifiers. Three detector types cover the 0.6-4 micron spectral range with a noise equivalent power (NEP) of approximately 10 to the -16th per sq rt Hz for two of the types and potential improvement to this performance for the third. Lower NEPs can be anticipated at longer IR wavelengths.

Rieke, G. H.↗
NASA NTRS1981

A model for dwarf novae as progenitors of Type I supernovae

It is suggested that a Type I supernova event can be produced as a result of accretion at low rates (less than 10 to the -10th solar mass/year) onto the white dwarf component of a dwarf-nova close binary. At these low rates, diffusion of the CNO nuclei out of the accreted hydrogen envelope can occur on the accretion time scale, and nuclear burning will occur mainly by the proton-proton chain. Studies of this process show that, when the CNO abundance in the envelope is less than 0.0025 of solar, no thermonuclear flash occurs and no mass is lost. The result of the evolution is a gradually increasing layer of helium beneath the hydrogen-burning shell.

Starrfield, S.↗
NASA NTRS1980

Surface composition changes in massive star evolution with mass loss

A series of evolutionary models of 40-100 solar mass objects undergoing mass loss are constructed with the explicit inclusion of the surface composition of H, He, C, N, O elements. Mass loss rates similar to those observed in Of stars, 4 to 7 x 10 to the -6th solar masses/yr, result in an appearance at the surface of equilibrium CNO products, i.e. enhanced nitrogen and diminished carbon, while that star is still burning hydrogen in the core. This result obtains because the initial convection core is a relatively large fraction of the total mass and rather modest loss exposes levels of anomalous composition. It is suggested that these objects might reasonably be identified as those luminous late type WN stars still containing surface hydrogen.

Noels, A.↗
NASA NTRS1981

Electron spectroscopy of the diamond surface

The diamond surface is studied by ionization loss spectroscopy and Auger electron spectroscopy. For surfaces heated to temperatures not exceeding 900 C, the band gap was found to be devoid of empty states in the absence of electron beam effects. The incident electron beam generates empty states in the band gap and loss of structure in the valence band for these surfaces. A cross section of 1.4 x 10 to the -19th sq cm was obtained for this effect. For surfaces heated to temperatures exceeding 900 C the spectra were identical to those from surfaces modified by the electron beam. The diamond surface undergoes a thermal conversion in its electronic structure at about 900 C.

Pepper, S. V.↗
NASA NTRS1980

Submicron particles in meteor streams

Submicron particles (mass less than 10 to the -15th g) were observed in certain meteor streams by impact detectors on satellite Explorer 46. This unexpected finding leads to conclusions about the nature and origin of the particles and about the importance of nongravitational forces.

Singer, S. F.↗
NASA NTRS1980

Evidence for ice meteoroids beyond 2 AU

Processes controlling the population of particles of mass greater than 2 x 10 to the -9th g as observed by the Pioneer 10 meteoroid penetration data between 2 and 5 AU are discussed as evidence for the presence of ice meteoroids. Consideration is given to particle collisional lifetimes, Poynting-Robertson drag and the influence of Jupiter in controlling particle orbits, and it is noted that none of these mechanisms may be capable of accounting for the observed constant, or possibly increasing, particle density between 2 and 5 AU. It is shown, however, that ice particles with radii of about 15 microns and varying amounts of impurities could account for the observed distribution with thermal sublimation or solar wind sputtering possible mechanisms of particle destruction. It is concluded that meteoroids made of ice are probably responsible for most of the penetrations of the Pioneer 10 meteoroid penetration sensor beyond 2 AU.

Zook, H.↗
NASA NTRS1981

Detection of interstellar OH in the far-infrared

Strong absorption lines of OH have been detected at wavelengths of 119.23 and 119.44 microns in the direction of Sgr B2. The lines arise from the 2Pi3/2, J = 5/2-3/2 transitions and imply a column density of N(OH) not less than 2.7 x 10 to the 15th/sq cm. The LSR Doppler velocity of the absorption features is close to zero; this suggests that material is being seen from both the +62 km/s and -90 km/s clouds at radio wavelengths. In addition, the detection of the same two lines in emission from the shocked region of the Orion Nebula has been made possible. The indicated intensity of these lines is 1.6 x 10 to the -17th W/sq cm, which implies a column density of shocked OH of about 3.6 x 10 to the 15th/sq cm.

Storey, J. W. V.↗
NASA NTRS1980

Temperature dependence of the reaction O/3P/ + OH/2 Pi/ yields O2 + H

Measurements of the absolute rate and temperature dependence of the rate constant for the reaction of ground state atomic oxygen with hydroxyl radicals to yield molecular oxygen and hydrogen atoms over the temperature range 211-499 K are presented. The reaction was monitored in a low-pressure discharge flow resonance fluorescence apparatus under pseudo-first-order conditions in which the oxygen concentration was greater than the hydroxyl concentration. An expression for the temperature dependence of the rate constant is derived from a least-squares fit to the observed bimolecular rate constants, which were found to range from 3.21 to 2.77 x 10 to the -11th cu cm/molecule per sec for temperatures from 211 to 499 K, indicative of a slight negative temperature dependence. Results are compared with those of previous workers, and the significance of the lower value of the rate constant obtained in the present study to models of HO(x) in the upper stratosphere is indicated.

Lewis, R. S.↗
NASA NTRS1981

Limit on galactic 6.13 MeV gamma-ray line

The University of New Hampshire large gamma-ray detector observed the galactic center region during a balloon flight from Alice Springs, Australia on 1977 November 21-22. The absence of any observable line at 6.13 MeV or its escape-peak energy makes it possible to place an upper limit of 8.1 x 10 to the -4th photons/(sq cm s) at the 99% confidence level on the 0-16 de-excitation line at this energy from the galactic disk in the direction of the center. This limit restricts the interpretation given by Willett et al. (1979) of the line at 6.13 MeV which they observed while viewing the galactic anticenter. The present results indicate that it is highly unlikely that the line which these authors report is due to dark nebulae or the quiet sun. Possible explanations for their observation are atmospheric background, local production in the detector, a localized cosmic source in the direction of the galactic anticenter, or a statistical fluctuation.

Dunphy, P. P.↗
NASA NTRS1981

A companion quasar to 3C345

The discovery of a new quasistellar object (QSO) which presents the strongest evidence to date for the membership of quasars in rich clusters is reported. During X-ray observations of quasar 3C345, a serendipitous X-ray source located 8 arcmin northeast of the quasar was discovered. The observed flux of the new source is 3.2 x 10 to the -13th erg/sq cm/sec in the 0.5-4.5 keV band. Three separate observations over a six-month period failed to show intensity variability in excess of the statistical uncertainty in the count rate. The spectrum shows a modest signal-to-noise ratio but four strong emission lines. It is suggested that the redshift agreement between the two QSOs indicates a common membership in a cluster of galaxies which may well be a rich cluster.

Margon, B.↗
NASA NTRS1981

Relationship between energetic particles and plasmas in the distant plasma sheet

Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of 100 eV to 4 MeV in the earth's distant (30 to 40 earth radii) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from 10 to the -5th to 10 to the 5th per sq cm-sec-sr-keV, varying smoothly over the entire energy range both when the plasma is cold (about 1 keV) and hot (about 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (not less than 50 keV) tail described well by a power law. The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.

Sarris, E. T.↗
NASA NTRS1981

Simultaneous measurements of NO/x/, NO, and O3 production in a laboratory discharge - Atmospheric implications

Simultaneous measurements of NO(x) (NO + NO2), NO, and O3 production in a laboratory discharge show that within the uncertainties of the experiment, all of the NO(x) produced was NO, and no detectable enhancement of O3 after the discharge was observed. The laboratory experiments described gave an NO production rate of 5 + or - 2 x 10 to the 16th molecules/joule mole for a 100,000-1,000,000 joules/m spark. Assuming that the global dissipation of lightning energy is about 10 to the -8th joules/sq cm per sec (Dawson, 1980; and Hill et al., 1980), the NO production rate results in a global source of NO due to lightning of about 1.8 Mt(N)/yr, which is considerably lower than earlier estimates. This lower value for NO(x) production by lightning suggests that NO(x) emissions from anthropogenic sources, estimated to be at least 20 MT(N)/yr, may be the dominant source of NO(x) to the global troposphere. Furthermore, since most of the anthropogenic sources of NO(x) are located in the Northern Hemisphere, this new interpretation of the relative source strengths of this species favors a highly skewed asymmetric distribution of NO(x).

Levine, J. S.↗
NASA NTRS1981

Discovery of phase-locked variable polarization in an RS Canum Venaticorum-like star, HR 5110

Using measurements on 79 nights in 1980 January-August, it is established that the polarization in the ultraviolet (U band) varies synchronously on the known binary period of 2.6132 days, with a peak-to-peak amplitude of 0.03%. The pattern is mainly second harmonic in character, as typical of binary star examples such as Algol and Upsilon Her. Reflection by the cooler star, by a plasma concentration, or both, is suggested. The scale of the polarization seems to be consistent with Rayleigh scattering by neutral hydrogen on the cooler star, and a roughly lambda to the -4th wavelength dependence should be searched for. The QU curve suggests a sizeable inclination for the system, of about 45 deg, but this is preliminary. Separately, a possible weak periodicity might be present on a subsidiary period, conceivably related to a rotating star spot.

Barbour, M. S.↗
NASA NTRS1981

Some new results on shock chemistry in IC 443

New observations have been made of CO, CO-13, SiO, SO, H2CO, HCO(+), N2H(+), CS, OCS, HCN, and OH in the shocked clouds of IC 443. It is found that at position IC 443 B, (1) the shocked CO is optically thin; (2) the HCO(+)/CO abundance ratio is 4-9 x 10 to the -4 th, representing a tenfold enhancement over that of normal interstellar clouds; (3) there is no enhancement of SO or SIO, as occurs in Orion KL; and (4) there is optically thin preshock OH, confirming a hundredfold enhancement of the OH/CO ratio in the shock.

Denoyer, L. K.↗
NASA NTRS1980

Focal-plane optimization for detector noise limited performance in cryogenic Fourier transform spectrometer /FTS/ sensors

A study was performed to determine the optimum focal plane configuration including optics, filters and detector-preamplifier selection. The configuration was optimized particularly with respect to minimizing the noise level, but fabrication considerations for a cryogenic environment were also taken into account. The noise terms from source, background, detector electronics and charged particle radiation were quantitatively evaluated. It appears that noise equivalent spectral radiance less than 10 to the -11th W/sq cm per sr per kayser can be achieved between 2.5 and 20 microns.

Mcguirk, M.↗
NASA NTRS1981

The HEAO-1 soft X-ray survey of cataclysmic variable stars

A survey of the soft X-ray emission from 206 cataclysmic variable stars, including dwarf novae in optically quiescent states, classical novae, recurrent novae, nova-like objects and polars, is reported. This is an extension of a previous survey of dwarf novae in outbursts by Cordova et al. (1980). The number of surveyed stars that correspond to features greater than 2 sigma is not in excess of the number of chance coincidences expected on the basis of a random sample of positions distributed over the entire sky. While a few cataclysmic variables have been previously identified as X-ray sources, the results of this survey imply that cataclysmic variables as a class must be, at best, low-luminosity X-ray sources with fluxes below the HEAO-1 A2 detector's sensitivity limit of a few times 10 to the -11th erg/sq cm-s in the energy range 0.1-3 keV. The X-ray luminosities of the cataclysmic variables are consistent with predictions from disk accretion models, provided that a wide range of accretion rates apply.

Cordova, F. A.↗
NASA NTRS1981

A kinetics study of the reaction of SO2 with CH3O2

The reaction of CH3O2 with SO2 has been studied using the flash photolysis/ultraviolet absorption technique. In contrast to previous measurements, no reaction could be detected over the temperature range 298-423 K. An upper limit of 5 x 10 to the -17th cu cm/molecule/sec has been determined for the reaction rate constant.

Sander, S. P.↗