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At least 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On the detection of newly created CN radicals in comets

A description is presented of laboratory measurements concerning the amount and the distribution of energy released into newly formed radicals by the photodissociation process. The experimental method used involved flash photolysis of the parent compound followed by laser induced fluorescence detection of the CN fragment. This method allowed the detection of individual rotational lines and, thereby, a monitoring of the relative populations of the vibrational-rotational levels of the CN ground state. The results obtained in the investigation suggest the possibility of observing emission lines in cometary spectra from newly formed CN radicals. Calculations show that it is feasible with present observational techniques to detect photochemically excited lines in the 0-0 band of the violet system.

Donn, B.↗
NASA NTRS1978

The distribution and mass of iron in the intracluster space of rich clusters of galaxies

It is shown that intracluster (IC) iron, whose presence is deduced from observations of an X-ray emission feature in the spectra of some X-ray clusters, could not have sedimented in the cluster core in a Hubble time. It is therefore concluded that the iron and gas are likely to be similarly distributed. Estimates of the total IC iron mass are given, and the possibility that the iron has been convected to the IC space by galactic winds from the visible cluster galaxies is briefly considered.

Rephaeli, Y.↗
NASA NTRS1979

Video detection and analysis techniques of transient astronomical phenomena

Low-light-level television systems have been utilized to gain information on meteors, aurorae, and other faint, transient astronomical phenomena. Such phenomena change not only their position as a function of time, but also their photometric and spectral characteristics in as little as 1/60 second, thus requiring unique methods of analysis. Data observed with television systems and recorded on video tape have been analyzed with a system utilizing both analog and digital techniques. Both off-the-shelf equipment and inhouse developments are used to isolate sequences of moving images and to store them in a form suitable for photometric and spectral reduction. Current emphasis of the analysis effort is directed at the measurement of the first-order emission lines of meteor spectra, the results of which will yield important compositional information concerning the nature of the impinging meteoroid.

Clifton, K. S.↗
NASA NTRS1981

Investigations related to evaluation of ultramicrofluorometer

High resolution emission and excitation fluorescent spectra were obtained for several samples in an effort to determine the optimum operational design for the instrument. The instrument was used to determine the required nature of a sample which could be detected, and in so doing, several different sample preparation techniques were considered. Numerous experiments were performed to determine the capabilities of the instrument with regard to the detection of suitably prepared virus specimens. Significant results were obtained in several areas. The fluorescent spectra indicated that substantial changes in the laser might be used advantageously to greatly improve the performance of the instrument. In the existing configuration, the instrument was shown to be capable of detecting the presence of suitably prepared virus samples.

Whitcomb, B.↗
NASA NTRS1981

Arcs in Saturn's radio spectra

Arcs appearing in the dynamic spectra of Saturn radio emission have been modelled using the same techniques as applied to Jovian arcs. Their properties suggest a source region several tenths of a Saturn radius above the cloud tops in the late morning local time sector.

Thieman, J. R.↗
NASA NTRS1981

Albedo, internal heat, and energy balance of Jupiter - Preliminary results of the Voyager infrared investigation

Full disk measurements recorded by the 0.4-1.7 micron radiometer on Voyager 1 indicate a geometric albedo of 0.274 + or - 0.013. This measurement and the Pioneer-based phase integral of 1.25 yield a Jovian Bond albedo of 0.343 + or - 0.032. Infrared spectra yield a thermal emission of 1.359 + or - 0.014 x .001 W/sq cm, which corresponds to an equivalent blackbody temperature of 124.4 + or - 0.3 K. In addition, the internal heat flux of Jupiter is estimated to be 5.444 + or - 0.425 x .0001 W/sq cm, and the energy balance defined as the ratio of emitted thermal to absorbed solar energy is 1.668 + or - 0.085.

Hanel, R. A.↗
NASA NTRS1985

Theoretical and Experimental Beam Plasma Physics (TEBPP)

The theoretical and experimental beam plasma physics (TEBPP) consists of a package of five instruments to measure electric and magnetic fields, plasma density and temperature, neutral density, photometric emissions, and energetic particle spectra during firings of the particle injector (SEPAC) electron beam. The package is deployed on a maneuverable boom (or RMS) and is used to measure beam characteristics and induced perturbations in the near field ( 10 m) and mid field (10 m to 100 m) along the electron beam. The TEBPP package will be designed to investigate induced oscillations and induced electromagnetic mode waves, neutral and ion density and temperature effects, and beam characteristics as a function of axial distance.

Roberts, W. T.↗
NASA NTRS1985

Nondispersive X-ray spectroscopy and imaging of plasmas using a charge-coupled device

A virtual-phase charge-coupled device (CCD) was used to obtain pinhole images and X-ray spectra of laser-produced, solid target plasmas. With the CCD used in the single-photon counting mode, the spectrum in the energy range 2-10 keV was obtained without a dispersive element. Typical spectra reveal two distinct temperatures: a cold component of approximately 200 eV and a hot component of approximately 5 keV. Also, multiline spectra comprising characteristic line emission (K alpha, K beta) from a multilayer target bombarded by beta-rays were recorded using a three-phase CCD. The results demonstrate the potential of CCDs as imaging spectrometers with application in space, laboratory, and fusion-plasma research.

Marsh, K.↗
NASA NTRS1986

Theoretical and Experimental Beam Plasma Physics (TEBPP)

The theoretical and experimental beam plasma physics (TEBPP) consists of a package of five instruments to measure electric and magnetic fields, plasma density and temperature, neutral density, photometric emissions, and energetic particle spectra during firings of the particle injector (SEPAC) electron beam. The package is developed on a maneuverable boom (or RMS) and is used to measure beam characteristics and induced perturbations field ( 10 m) and mid field ( 10 m to 100 m) along the electron beam. The TEBPP package will be designed to investigate induced oscillations and induced electromagnetic mode waves, neutral and ion density and temperature effects, and beam characteristics as a function of axial distance.

Roberts, B.↗
NASA NTRS1986

Ionized polycyclic aromatic hydrocarbons in space

The mid-infrared spectrum of a continuously increasing number of stellar objects, planetary and reflection nebulae, H-II regions and extragalactic sources show a distinctive set of broad emission features at 3.3, 3.4, 6.2, 7.7, 8.6, and 11.3 micron known collectively as the unidentified infrared emission bands. A model is summarized in which the bands arise from positively charged polycyclic hydrocarbons (PAH's) on the basis of their low ionization potential and the excellent agreement between the emission bands and laboratory spectra of auto exhaust which contains these types of molecules. The proposed presence of PAHs in such a variety of objects points to their presence in the interstellar medium. Out of a previously published collection of solid state PAH radical cation spectra five were selected on the basis of the unique thermodynamic stability of their carrier and compared directly to the wavelengths of the DIB's. Although the match seems quite favorable, strongly suggesting that PAH radicals are the long sought after carrier of the diffuse interstellar absorption bands, much laboratory work must be done to test this hypothesis.

Barker, J.↗
NASA NTRS1986

Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

Bhattacharya, P. K.↗
NASA NTRS1986

A two-dimensional intensified photodiode array for imaging spectroscopy

The Johns Hopkins University is currently developing an instrument to fly aboard NASA's Space Shuttle as a Spartan payload in the late 1980s. This Spartan free flyer will obtain spatially resolved spectra of faint extended emission line objects in the wavelength range 750-1150 A at about 2-A resolution. The use of two-dimensional photon counting detectors will give simultaneous coverage of the 400 A spectral range and the 9 arc-minute spatial resolution along the spectrometer slit. The progress towards the flight detector is reported here with preliminary results from a laboratory breadboard detector, and a comparison with the one-dimensional detector developed for the Hopkins Ultraviolet Telescope. A hardware digital centroiding algorithm has been successfully implemented. The system is ultimately capable of 15-micron resolution in two dimensions at the image plane and can handle continuous counting rates of up to 8000 counts/s.

Tennyson, P. D.↗
NASA NTRS1987

The triple radio source 0023 + 171 - A candidate for a dark gravitational lens

In the course of a radio-optical search for gravitational lenses, a multiple radio source, 0023 + 171, was discovered, which has two optical counterparts at z = 0.946 separated by 5 arcsec. Their redshifts are the same within the measurement error, and their optical spectra show the same emission lines with the same relative intensities. One interpretation of these measurements is that the images of 0023 + 171 are gravitationally lensed. However, because the radio morphology is complex and the optical objects are faint, the existing data cannot exclude another interpretation, i.e., that the components of 0023 + 171 are two physically associated radio galaxies or two components of a single galaxy. The only possible evidence in favor of a lensing object is extremely faint optical emission located approximately 1 arcsec from one of the images. If this multiple source is indeed gravitationally lensed, the combination of available data imply a mass-to-light ratio for the lensing matter equal to about 1000.

Hewitt, J. N.↗
NASA NTRS1988

Composition and size of Apollo asteroid 1984 KB

The Class S object-typifying spectral signatures of olivine, pyroxene, and NiFe metal are noted in the present reflection spectra and thermal-emission radiometric data for the earth orbit-crossing Apollo object, 1984KB; a surface material akin to the rare lodranite meteorites. While the Class S object identification is strengthened by standard asteroid thermal model's indication of an about 0.7-km radius, and albedo of about 0.16, which is inconsistent with the IR spectrum, is obtained by an analysis of the same thermal data with a bare-rock thermal model. The object must have a significant regolith despite its small size.

Bell, Jeffrey F.↗
NASA NTRS1988

Submillimeter measurement of stratospheric chlorine monoxide

The measurement of the ClO concentration in the stratosphere provides crucial information on the mechanism for ozone depletion by catalytic reactions involving chlorine. Two rotational transitions of ClO, J = 35/2 - 33/2 and J = 37/2 - 35/2 have been identified in balloon-borne high-resolution spectra of the stratospheric emission in the submillimeter region. The measurements provide information on the ClO concentration at altitudes around 28 km. In the case of afternoon measurements obtained in April 1979, a scaling factor of 0.85 (+0.67, -0.64) is observed, and in the case of afternoon and early morning measurements obtained in October 1982, a scaling factor of 0.88 (+0.18, -0.08) is observed.

Carli, B.↗
NASA NTRS1990

The redshift peak at z = 0.06

A catalog of galaxies whose optical spectra contain strong broad emission lines and continua, probably of nonthermal origin, has been completed. The catalog contains about 900 objects, about 700 of which have z of 0.2 or less. A histogram of the redshift distribution for all of the objects in the redshift range 0.02-0.2 and with a large peak at z = 0.06 is shown. Possible interpretations of the peak, which was first seen in 1968, are considered. It is concluded that the only way to explain the peak (and others like it that make up a series of peaks) and still maintain the cosmological redshift hypothesis is to go to cosmological models in which the universe has a multiply connected topology.

Burbidge, G.↗
NASA NTRS1991

Dust scattering in the high-state eclipse of Cen X-3

Exosat data from two high-state eclipses of Cen X-3 are analyzed for the effects of dust scattering. The light curves show bright (2 per cent of the out-of-eclipse flux), smoothly varying emission which reaches its minimum after mideclipse. Of this emission, the soft flux falls monotonically with orbital phase. This soft component with dust scattering is identified and spectral models are fitted to the asymmetric emission, that is, to spectra obtained by subtracting from a spectrum at a given orbital phase before phase zero the corresponding spectrum from the equal and opposite phase after phase zero. It is found that the model of Molnar and Mauche, used to fit dust scattering in Cyg X-3, can explain the observed spectra and yields values for the distance to Cen X-3 and for the size of the dust grains of 5.4 kpc and 0.33 micron, consistent with previous observations in other wavebands.

Day, C. S. R.↗
NASA NTRS1991

Systematic displacements between gas and dust in the sunward fans of two low-activity comets

The unusual displacements between the radical emission-line gas and the scattered-light dust continuum of IRAS-Araki-Alcock (1983 VII) and P/Tempel 2 (1988 IXV) are presented. Two-dimensional spectral images were flattened by dome flats and twilight skyflats, and the actual sky subtraction was obtained by sequentially observing clear patches of sky before and after the cometary integrations. A set of slight distributions were obtained along the solar radius vector through the 'optocenter' toward the antisolar direction. Spectral-spatial cross cuts are illustrated, and the continuum and the emission-line regions in the panels are shown. The continuum of IRAS-Araki-Alcock is found to be much stronger than the cometary comae emissions near the nucleus. For the spectra of the relatively faint Comet P/Tempel 2, both dust and gas emission are weaker, and some 'derivatives' remain.

Spinrad, Hyron↗