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NASA NTRS1982

Chromospheric, transition layer and coronal emission of metal deficient stars

It is shown that while MgII k line emission decreases for metal deficient stars, the Ly alpha emission increases. The sum of chromospheric hydrogen and metallic emission appears to be independent of metal abundances. The total chromospheric energy loss is estimated to be 0.0004 F sub bol. The chromospheric energy input does not seem to decrease for increasing age. The transition layer emission is reduced for metal deficient stars, but it is not known whether the reduction is larger than can be explained by curve of growth effects only. Coronal X-ray emission was measured for 4 metal deficient stars. Within a 12 limit it could still be consistent with the emission of solar abundance stars.

Boehm-Vitense, E.↗

NASA NTRS1982

The ABAG biogenic emissions inventory project

The ability to identify the role of biogenic hydrocarbon emissions in contributing to overall ozone production in the Bay Area, and to identify the significance of that role, were investigated in a joint project of the Association of Bay Area Governments (ABAG) and NASA/Ames Research Center. Ozone, which is produced when nitrogen oxides and hydrocarbons combine in the presence of sunlight, is a primary factor in air quality planning. In investigating the role of biogenic emissions, this project employed a pre-existing land cover classification to define areal extent of land cover types. Emission factors were then derived for those cover types. The land cover data and emission factors were integrated into an existing geographic information system, where they were combined to form a Biogenic Hydrocarbon Emissions Inventory. The emissions inventory information was then integrated into an existing photochemical dispersion model.

Carson-Henry, C.↗

NASA NTRS1983

Identification of radio emission from the Io flux tube

The identification of a specific Jovian decametric emission with the particular flux tube near the orbit of Io giving rise to it would substantially improve theoretical understandings of the relation of the Io flux tubes with the arc-like structures seen on time vs. frequency plots of decametric emissions observed by the Voyager spacecraft. The present paper shows how the instantaneous Io flux tube may be identified with particular emission features. It is demonstrated that the emissions designated Io caused emission (ICE) may be interpreted as representing sections of arc structures emitted by the interaction of Io with successive flux tubes. The model is capable of accounting for the change of displacement angle of the ICE structures as the sub-observed Jovian longitude changes. The identification permits the mapping of emissions onto the causative flux tubes for Jovian longitudes from 240 to 360 deg.

Riddle, A. C.↗

NASA NTRS1984

The mysterious 10 micron emission feature in the spectrum of Nova Aquilae 1982

Broad-band 1.2-23 micron photometry and 1 percent resolution 7-14 micron spectrophotometry of Nova Aql 1982 are presented. This nova developed similarly to other dusty novae in that the appearance of thermal infrared emission from a circumstellar dust shell was coincident with a downward transition at visual wavelengths. A strong 10 micron emission feature appeared in the spectrum of Nova Aql 1982 during the dust shell development phase. This feature was not entirely similar to emission features previously observed in other stars with circumstellar shells. The contrast of the nova's 10 micron feature was larger than those observed in the SiC-rich shells of carbon stars. On the other hand, although the nova emission feature was reminiscent of the 10 micron silicate emission feature observed in oxygen-rich supergiants, it peaked at a slightly longer wavelength and there was no corresponding 20 micron emission feature. The contrast of the feature increased with time. It is concluded that an anomalous dust grain component, tentatively identified as SiC, nucleated and grew in the circumstellar shell of Nova Aql 1982.

Ney, E. P.↗

NASA NTRS1985

Fracto-emission from single fibres of Kevlar

Fracto-emission (FE) is the emission of particles (e.g. electrons, ions and photons) during and following fracture. In this paper, we present data on electron emission (EE) and positive ion emission (PIE) from the tensile fracture of Kevlar single fibers. The fibers were initially fractured in pure tension, where a stranded form of fracture was observed, often with multiple peaks spread over several hundred microseconds. The loading condition was then changed by stretching and breaking the fibers over a dull metal edge. With this change in the loading, different forms of fracture were observed, each with distinctive forms of emission curves. When fracture was accompanied by extensive fibril formation, total emission was high and both EE and PIE decay times were long relative to fractures in which little fibril formation occurred. The results of this study suggest that FE has some applicability as a tool for the detection of fracture mechanisms of single fibers.

Dickinson, J. T.↗

NASA NTRS1985

Textured carbon on copper: A novel surface with extremely low secondary electron emission characteristics

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for a range of primary electron beam energies and beam impingement angles are presented for a series of novel textured carbon surfaces on copper substrates. (All copper surfaces used in this study were oxygen-free, high-conductivity grade). The purpose of this investigation is to provide information necessary to develop high-efficiency multistage depressed collectors (MDC's) for microwave amplifier traveling-wave tubes (TWT's) for communications and aircraft applications. To attain the highest TWT signal quality and overall efficiency, the MDC electrode surface must have low secondary electron emission characteristics. While copper is the material most commonly used for MDC electrodes, it exhibits relatively high levels of secondary electron emission unless its surface is treated for emission control. The textured carbon surface on copper substrate described in this report is a particularly promising candidate for the MDC electrode application. Samples of textured carbon surfaces on copper substrates typical of three different levels of treatment are prepared and tested for this study. The materials are tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near-grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the textured surfaces are compared with each other and with those of untreated copper. All the textured carbon surfaces on copper substrate tested exhibited sharply lower secondary electron emission characteristics than those of an untreated copper surface.

Curren, A. N.↗

NASA NTRS1986

Radio continuum emission from winds, chromospheres, and coronae of cool giants and supergiants

The results of a sensitive VLA radio survey of the single cool-wind giants and super giants stars, having spectral types in the range (G0-M5), are presented. The survey was carried out at 6 cm using the NRAO VLA. The results of the observations are discussed in the context of the various mechanisms which might be producing radio emission in the cool stars. One coronal giant was detected as well as six cool-wind giants in the range 2-6 cm at levels of 0.1-2 mJy. The six-cm emission of the coronal giant alpha Aurigae is shown to be optically thin having free-free emission from the corona of energy 10 to the 7th K. The 2-cm emission from alpha Aur also contains contribution of about 65 percent from the stellar disk of one or both stars. The radio emission from all other sources is explained as optically thick emission from stellar winds. The inferred ionized mass-los rates for the cool wind stars was about 10 to the 10th solar mass per year for MK III-type stars and 10 to the -9th solar mass per year for MK II type stars.

Drake, S. A.↗

NASA NTRS1985

A model investigation of the impact of increases in anthropogenic NOx emissions between 1967 and 1980 on tropospheric ozone

The impact of anthropogenic NOx emission on tropospheric ozone has been investigated. Two statistical models were used for estimating annual global emissions of NOx and for driving the trend in the emission for the years 1966-1980. Both models show a steady increase in the NOx emission, except for two brief periods of leveling off: after 1973 and after 1978. The impact was estimated by calculating the rates of emissions as functions of latitude, longitude, and year, with a one-dimensional (latitudinal) model, which included coupled tropospheric photochemistry and diffusive meridional transport. Steady-state photochemical calculations with prescribed NOx emissions appropriate for 1966 and 1980 indicate an ozone increase of 8-11 percent in the Northern Hemisphere, a result compatible with the rise in ozone suggested by the observations.

Dignon, J.↗

NASA NTRS1985

X-ray images of W28 and 3C400.2 - Two radio-shell supernova remnants with centrally-peaked X-ray emission

X-ray images of the supernova remnants (SNRs) W28 and 3C400.2 were obtained using the Imaging Proportional Counter (IPC) on the Einstein Observatory. Despite the shell-like radio morphology of these remnants, their X-ray emission is centrally peaked. Two possible X-ray emission mechanisms are explored: synchrotron emission due to an active central pulsar, and thermal emission from a thin hot plasma filling the interior of the remnant. Comparisons of X-ray and radio properties of W28 and 3C400.2 with known Crab-like remnants suggest that synchrotron emission is not a very plausible X-ray emission mechanism. Optical and radio observations suggest that both SNRs exploded in a dense cloud and have evolved rapidly to the radiative stage. The X-ray morphology observed is similar to that predicted for SNRs in such an environment.

Matsui, Y.↗

NASA NTRS1986

Infrared absorption and emission characteristics of interstellar PAHs

The mid-infrared interstellar emission spectrum with features at 3.28, 6.2, 7.7, 8.7 and 11.3 microns is discussed in terms of the Polycyclic Aromatic Hydrocarbon (PAH) hypothesis, which is based on the suggestive, but inconclusive comparison between the interstellar emission spectrum with the infrared absorption and Raman spectra of a few PAHs. The fundamental vibrations of PAHs and PAH-like species which determine the IR and Raman properties are discussed. Interstellar IR band emission is due to relaxation from highly vibrationally excited PAHs excited by ultraviolet photons. The excitation/emission process is described and the IR fluorescence from one PAH, chrysene, is traced. Generally, there is sufficient energy to populate several vibrational levels in each mode. Molecular vibrational potentials are anharmonic and emission from these higher levels will fall at lower frequencies and produce weak features to the red of the stronger fundamentals. This process is also described and can account for some spectroscopic details of the interstellar emission spectra previously unexplained. Analysis of the interstellar spectrum shows that PAHs contain between 20 and 30 carbon atoms are responsible for the emission.

Barker, J. R.↗

NASA NTRS1986

Rocket observations of ultraviolet and optical emissions in the dayside aurora

Observations of the emissions extending from the UV to the near-IR region of the spectrum obtained at Cape Parry, Canada on December 7, 1981 are examined. The flight path of the rocket used to obtain the observations, launch conditions, and optical and UV instruments for measurement of the emission from the cleft precipitation region are described. Emission rates and altitude and zenith angles for emission features O I (989 A), O I (1304 A), O I (1356 A), O I (6300 A), O I (7774 A), O I (8446 A), H I (1216 A), and O II (834 A) are studied. The particle energy flux for the emission feature are estimated. The data suggested that there is an emission layer at 250-300 km.

Christensen, A. B.↗

NASA NTRS1987

Observation of the O I ultraviolet intercombination emissions in the terrestrial dayglow

The first measurement of the 1173-A O I intercombination line in emission in the terrestrial dayglow was performed using the EUV-FUV spectrometer designed to be flown with the Astro-1 observatory. The atmospheric conditions and viewing geometry were such as to suppress nitrogen emission relative to those from atomic oxygen, permitting the identification and measurement of the weak O I 1173-A intercombination multiplet and the 1641-A line as well as the strong 989-A and 1304-A emissions. At lower altitudes, the 1173-A emission rate increased while the 989-A emission, from the same upper level, decreased. This behavior is consistent with the radiative entrapment model of Meier (1982) and the laboratory value of the 1173-A/989-A branching ratio measured by Morrison (1985). The 1641-A/1304-A emission ratio is also consistent with a radiative entrapment model.

Bowers, C. W.↗

NASA NTRS1987

A method for remote sensing the emissivity, fractional cloud cover and cloud top temperature of high-level, thin clouds

A methodology for retrieving the emissivity, cloud cover and cloud top temperature of high-level, thin clouds is developed and described. In the thermal infrared windows, the outgoing radiances from the earth's atmosphere contain information about cloud emissivity and cloud top temperature. This information is clearly demonstrated in the brightness temperature difference curves of two window channels. For the purpose of illustration, two window channels centered at 810 and 930 cm are chosen to construct the brightness temperature difference curves for a range of cloud top temperatures. These curves vary for different cloud top temperatures, and along each of these curves the emissivity changes. The brightness temperature difference method is used in a simulation study to demonstrate the feasibility of retrieving the cloud top temperature and emissivity by the utilization of measurements in two window channels. As expected, a perfect retrieval is found if perfect measurements and ideal atmospheric conditions are assumed. If a random error, which has a normal distribution with a mean of zero and standard deviation of + or - 0.5 C, is imposed to the measurements, a reasonable retrieval is found for emissivity greater than 0.3. The algorithm has been applied to a limited amount of HIRS2 data, which has 3.7, 3.98 and 11 micron channels. The cloud top temperature, emissivity and cloud cover are determined by using these channels.

Wu, Man-Li C.↗

NASA NTRS1987

Infrared absorption and emission characteristics of interstellar PAHs

Allamandola, L. J.↗

NASA NTRS1988

Satellite observations of a new type of discrete VLF emission at L below 4

A new type of discrete whistler mode emission has been observed in the magnetosphere at L below 4. The emission elements are confined to a bandwidth of 1-5 kHz, with the lower cutoff frequency of the band varying with L shell, being equal to about 0.2-0.5 f(Heq), where f(Heq) is the equatorial electron gyrofrequency. The discrete and burstlike nature of the emissions is similar to that of chorus emissions typically observed at higher L; however, dispersion of individual elements is often different from typical chorus, and the emissions are observed inside as well as outside the plasmapause. The phenomenon seems to occur mainly in the early morning local time sector and is well correlated with geomagnetic activity, occurring mostly at high gasmagnetic activity. The analysis of data from the low-altitude ISIS-2 and the high-altitude De-1 satellites indictes that the emissions may be generated near the equatorial plane at frequencies of about 0.2 f(Heq) inside and about 0.35 f(Heq) outside the plasmapause. The parallel energy of electrons for gyroresonance with the observed waves is found to be about 20-50 keV in both cases.

Poulsen, W. L.↗

NASA NTRS1988

UV resonance line dayglow emissions on earth and Jupiter

The similarities and differnces between atomic resonance line emissions on earth and Jupiter are studied. For earth, the scattering of the conservative atomic oxygen triplet transition at 1304 A and the nonconservative atomic oxygen sextuplet at 989 A is considered. For Jupiter, the scattering of the conservative atomic hydrogen doublet at 1216 A and the nonconservative atomic hydrogen doublet at 1026 A are addressed. Models are presented for the intensities of the emission features as seen from a distance of several planetary radii, using the same observational geometry for both earth and Jupiter. Variations of the line-integrated emissions across the disk and near the limb of each planet are examined in detail. Line profiles for the emission near the limb and at disk-center are also studied. The models reveal the importance of including inhomogeneities and temperature variations of the atmosphere in scattering models, and indicate that outer planet emissions previously interpreted as 'electroglow' may be solely due to resonant scattering of solar emissions.

Gladstone, G. Randall↗

NASA NTRS1989

Transient coronal extreme ultraviolet emission before and during the impulsive phase of a solar flare

Transient coronal EUV emission, recorded in an emission line of Fe XI at 180.4 A, has been observed prior to and during the initial stages of a solar flare. This emission provides direct evidence of the interactions between the lower corona and the chromosphere during flare initiation. The first EUV enhancement was correlated with activation and eruption of a filament, extended over a distance of about 120,000 km, and had an emission maximum at the site of filament disruption. A moving source of EUV emission also appeared along the trajectory of the erupting filament as it accelerated through the low corona. The mass of this source is estimated to be greater than that of the initial filament or surrounding corona, implying an additional mass ejection from the chromosphere. EUV emission during the impulsive phase of the flare consisted of transient sources along the photospheric magnetic neutral line, with intervening regions of lesser intensity that are interpreted as transient coronal loops below the erupting filament.

Neupert, Werner M.↗

NASA NTRS1988

Optical emission diagnostics of electron cyclotron resonance and glow discharge plasmas for a-Si:H and a-SiC:H film depositions

It is demonstrated that the steady-state and kinetic characteristics of ECR (electron cyclotron resonance) and RF glow discharge plasmas can be readily monitored by OES (optical emission spectroscopy) in real time during a-Si:H and a-SiC:H film depositions using an OMA detection system. The ECR and RF glow discharge plasmas used for a-Si:H and a-SiC:H film depositions were studied by monitoring the emission of SiH(asterisk), H(asterisk), H(asterisk)2, and CH(asterisk) excited states. The OES of the ECR plasma shows a strong emission at 434 nm from H(asterisk), which is not detectable in the glow discharge plasma. Steady-state OES studies have established preliminary correlations between SiH(asterisk) and CH(asterisk) emission intensities and the film deposition rate. Transient OES spectra of SiH4 and CH4 plasmas have shown different kinetics in SiH(asterisk) and CH(asterisk) emission intensities. Transient studies of the SiH(asterisk) emission intensity have indicated that additional mechanisms for producing the SiH(asterisk) species become evident in hydrogen-diluted silane plasmas.

Yang, C. L.↗