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NASA NTRS1975

Denouement of Jovian radiation belt theory

Predictions of theoretical models of Jupiter's radiation belts are compared with Pioneer 10 measurements. A brief quasi-historical review is given of the evolution of the basic theoretical ideas with emphasis on the three physical processes that were believed to be dominant in the Jovian electron fluxes: radial-diffusion transport, limitation of particle fluxes by plasma wave turbulence, and particle losses from collisional sweep-up by the Galilean satellites. Pioneer 10 data on the inner zone are discussed which yield the clearest evidence for radial diffusion being the dominant transport process, the synchrotron flux density is estimated using Pioneer 10 measurements, and the observed outer-zone electron fluxes are favorably compared with the qualitative and quantitative predictions of the whistler-mode stable-trapping model. The outer-zone electron-precipitation flux is estimated, and it is suggested that precipitation could affect the structure of the Jovian ionosphere. Satellite sweep-up is shown to be less severe than had been anticipated.

Coroniti, F. V.↗

NASA NTRS1976

Spectra and Fabry-Perot interferometry of AG Carinae and the nebula

Observations of the variable P Cygni-type supergiant and the unique ring nebula around it were made in 1974. Line identifications are tabulated, and an estimated electron density of 1700 per cu cm is combined with a radio flux density to derive a nebular mass of 0.18 (plus or minus 0.04) solar mass on the basis of a distance of 2 kpc. From the data, some ideas of the age and kinematics of the nebula are offered, tracing the evolution of P Cygni supergiants from the youthful prototype past the nebular stage of AG Carinae into more typical, relative old age without recognizable nebular envelopes.

Johnson, H. M.↗

NASA NTRS1976

Ultraviolet spectrometry of the inner solar system from Mariner 10

The significant results of Mariner 10 ultraviolet spectrometer observations of Mercury, the moon, the interplanetary medium, the comet Kohoutek, and Venus are summarized. The total surface pressure on Mercury was found to be less than (1-2) millionths mbar by the occultation experiment. Estimated number densities and upper limits for various species at the surface subsolar point of Mercury were obtained. Preliminary analysis of Kohoutek data shows possible detection of O and C associated with the comet head. Emissions from Lyman alpha in the interplanetary medium show maximum and minimum intensity directions that can be fitted by a model in which the interstellar wind penetrates the heliosphere from a direction of about 252 deg right ascension and -17 deg declination with a velocity of about 20 km/sec. There is evidence for a high-temperature scale height for hydrogen for Venus similar to that reported by Mariner 5.

Broadfoot, A. L.↗

NASA NTRS1977

On the physical conditions in the 'high-velocity' cloud near Zeta Ori

The problem of the 'high-velocity' clouds is rediscussed. Recent OAO-C Copernicus observations of lines of four atoms and ions have been used to estimate the density and temperature in both the 'high-velocity' and 'normal' interstellar clouds in the line-of-sight to Zeta Ori. The temperature and densities in the normal cloud are similar to previous results for interstellar clouds, yielding temperatures of the order of 100 K and compositions underabundant relative to the sun by factors of 3 or more. The high-velocity cloud, however, is warmer (at least 1000 K) and appears to have a normal solar abundance.

Drake, J. F.↗

NASA NTRS1978

Spontaneous emission near the electron plasma frequency in a plasma with a runaway electron tail

Spontaneous emission of radiation with frequencies near the electron plasma frequency is studied for a plasma which consists of both thermal and runaway electrons. It is found that a substantial enhancement of the spontaneous radiation intensity can occur in this frequency regime via a Cherenkov resonance with the runaway electrons. Numerical analysis indicates that, for reasonable estimates of densities and energies, the plasma-frequency radiation can attain levels greater than the peak thermal emission at the second gyroharmonic.

Freund, H. P.↗

NASA NTRS1979

The interstellar material in front of Chi Ophiuchi. I - Optical observations

Optical observations of the interstellar material in front of Chi Oph are discussed. The main interstellar cloud is made up of several regions with velocities between -6 and -12 km/s (heliocentric). Both CH and CH(+) are found within this feature, but with central velocities which differ by 2 km/s. Another cloud, with a velocity of -26 km/s, contains relatively strong Ca(+) lines. It has a ratio between Ca(+) and Na(0) column densities that is appropriate for 'high-velocity' clouds. Calcium, iron, and sodium column densities are used to estimate an average electron density for the line of sight, as well as for each cloud. The abundances of CH and CH(+), and the absence of CN, are analyzed in terms of current theories about their origin.

Frisch, P. C.↗

NASA NTRS1979

Preflare characteristics of active regions observed in soft X-rays

X-ray images from the AS&E telescope on Skylab are used to investigate coronal conditions in solar active regions during the 20-min periods preceding the X-ray onsets of small flares. The preflare or precursor phase is defined as a phase with a characteristic length or time scale significantly different from that of the rise phase. We show that there is no observational evidence of a requirement for a coronal preflare heating phase with a time scale longer than 2 min for small flares characterized by one or two loops. In 18 out of 25 cases the flaring X-ray structure was not the brightest feature in the preflare active region. The electron densities are estimated for preflare loops.

Kahler, S. W.↗

NASA NTRS1980

Outer atmospheres of cool stars. VI - Models for Epsilon Eridani based on IUE spectra of C II, Mg II, Si II, and Si III

Observations of the ultraviolet line spectrum of the active chromosphere star, Epsilon Eridani, obtained with the IUE satellite have been analyzed. The coupled statistical equilibrium and radiative transfer equations for the prominent transitions of C II, Mg II, Si II, and Si III. A satisfactory fit to all of the line strengths can be achieved with a model similar to that recently proposed to explain bright points on the quiet sun. A surface pressure at the base of the transition region of 0.5 dynes/sq cm is derived, which is a factor of 3 higher than the quiet sun value, but a factor of 3 smaller than predicted by scaling laws, assuming a conductively heated stellar transition region. It is found that the surface fluxes of the C II 1334, 1335 and Si III 1892 emission lines are good diagnostics of pressure at the base of the transition region, but line ratio techniques using the 1892 line for estimating electron densities may be valid.

Simon, T.↗

NASA NTRS1981

The energetics of molecular clouds. III - The S235 molecular cloud

The molecular cloud associated with the S235 H II region has been studied by means of molecular lines and near-infrared observations. The cloud consists of two components, one of which partly surrounds the S235 H II region. The other component contains a dense, hot region of active star formation, marked by self-reversed CO profiles, compact H II regions, masers, and infrared sources. From the molecular line data, the size and mass of the two components are estimated to be 6-8 pc and 3000-4000 solar masses. More detailed studies near the region of active star formation yield estimates of density (approximately 200,000-500,000/cu cm) and the abundances of H2CO, HCO(+), HCN, and (C-13)O. Analysis of the energetics suggests that the cloud is heated by the exciting star of S235 and by the exciting stars of the compact H II regions. Assuming that the gas is heated by collisions with warm dust grains, the far-infrared luminosity has been predicted. The observations of far-infrared emission are in reasonable agreement with predictions.

Evans, N. J., II↗

NASA NTRS1981

A planetary nebula with high oxygen abundance in the galactic bulge

Extensive photoelectric spectra of the planetary nebula H1-55 in the galactic bulge are obtained, and indicate that the object is overabundant in oxygen and nitrogen. Temperature and density are estimated, and chi-square tests are used to place confidence limits on the result. The logarithmic oxygen abundance is found to be 9.50, and the abundance of other heavy elements are also enhanced, such as N = 8.87, S = 7.4, and Ar = 7.4. Helium, sulfur, and argon abundances are affected by uncertainties in the corrections for unobserved ions, which remains consistent with the exceptionally low electron temperature of less than 5600 K. Results agree with the usual models of planetary nebula formation; and therefore, if H1-55 is formed like most planetary nebulae, there must be some very metal-rich stars in the galactic bulge.

Price, C. M.↗

NASA NTRS1984

Wet model of Saturn's ionosphere: Water from the rings

Current theoretical models of Saturn's ionosphere are difficult to reconcile with the ionospheric electron density profiles obtained from the Pioneer and Voyager radio occultation observations and the large diurnal variation of maximum ionospheric electron density deduced from studies of Saturn lightning discharges. A model of Saturn's ionosphere is proposed in which water plays a major role as a minor constituent present by virtue of downward diffusion from an external source. This model of the Saturn ionosphere is a classical 'F2' type layer resulting from the photodissociative production of H(+) from H2 and rapid chemical loss due to a series of charge exchange reactions with water. A planet-wide influx of about 4x10 to the 7th power molecules/sec/sq cm of water from the rings is consistent with the observed ionospheric electron densities and estimates of influx due to micrometeoride bombardment of the rings. An enhanced influx of water occurs at latitudes (-38 deg, +44 deg) magnetically connected to the inner edge of Saturn's B ring which results from an electromagnetic erosion process contributing substantially to the (local) upper atmosphere water content. Present day influx at these latitudes is possibly as large as 2x10 to the 9th power molecules/sec/sq cm.

Connerney, J. E. P.↗

NASA NTRS1984

CPD -48 deg 1577 - The brightest known cataclysmic variable

The discovery is reported of a V = 9.4 mag star which has the properties of a cataclysmic variable. Its UBV colors are similar to those of UX UMa, and its brightness fickers with an amplitude of the order of 0.1 mag. Larger brightness variations (0.5 mag) are found on a time scale of years. Its spectrum is characterized by extremely weak absorption lines of He I and He II, as well as extremely broad, shallow lines of H. A broad K line is very weakly present in absorption. Emission cores with a very slow decrement are seen in the H lines. From a comparison with the known properties of other cataclysmic variables, the distance, reddening, and mass exchange rate are estimated. The space density of cataclysmic variables is also estimated, since the original spectroscopic survey is complete to magnitude B = 10.0.

Krzeminski, W.↗

NASA NTRS1985

Nucleus-nucleus interaction above several hundred GeV/n

The Japanese-American Cooperative Emulsion Experiment (JACEE) have been investigating high energy nuclear interactions of cosmic ray nuclei by means of balloon-borne emulsion chamber. Current exposure parameters are listed. Analysis of the last two experiments (JACEE4 and JACEE5) are still in progress. A result of semi-inclusive analysis of a sample set of central collision events is presented here, concerning multiplicity, rapidity fluctuation for extremely high multiplicity events and correlation between transverse momentum and estimated energy density.

Burnett, T. H.↗

NASA NTRS1983

Surface density of quasars in two high-latitude fields

Fourty-four objects selected for ultraviolet excess have been identified spectroscopically. The objects lie in two Palomar 1.2 m Schmidt fields in the north galactic polar cap, one of 7.7 sq deg centered on Kapteyn Selected Area 29, the other of 36 sq deg centered on SA 55. The objects are characterized by Color Classes (CC) 1A, 1, 1B, 1C, 2, and 3. Quasars comprise 75 percent of the CC 1A objects and 44 percent of the objects in the SA 29 field. Twelve quasars in the SA 29 field comprise a complete sample to B = 18.5 mag, and given an uncorrected surface density of 1.6 quasars/sq deg. This value is essentially that derived by Sandage (1969). Corrections are applied to account for the lack of high redshift quasars. An empirical correction is derived to account for lack of simultaneity in selection and photometry. A corrected lower limit to the surface density is estimated to be 1.85 quasars/sq deg to B = 18.5 mag.

Usher, P. D.↗

NASA NTRS1984

Magnetic field amplification and generation in hypervelocity meteoroid impacts with application to lunar paleomagnetism

A one-dimensional numerical model for the expansion of impact-produced vapor clouds is used to investigate magnetic field generation mechanisms in events such as meteor collisions with the moon. The resulting cloud properties, such as ionization fraction, electrical conductivity, radial expansion velocity, mass density, and energy density are estimated. The model is initiated with the peak shock states and pressure thresholds for incipient and complete vaporization of anorthosite lunar surface materials by iron and GA composition meteorites. The expansion of the spherical gas cloud into a vacuum was traced with a one-dimensional explicit lagrangian hydrodynamic code. The hypervelocity impact plasmas produced are found to be significant in the amplitudes and orientations of the magnetic fields generated. An ambient magnetic field could have been provided by the core dynamo, which would have interacted with the expanding plasmas and formed induced paleomagnetic fields. Several other field-contribution mechanisms are discussed and discarded as potential remanent magnetism contributors.

Hood, L. L.↗

NASA NTRS1985

Determination of rarefied-flow aerodynamics of the Shuttle orbiter from flight measurements on STS-6 and STS-7

This report presents the flight data results from the High Resolution Accelerometer Package (HiRAP) experimment on the sixth and seventh Shuttle missions (i.e. STS-6 and STS-7). The data have been reduced to produce aerodynamic force coefficients, principally L/D in the rarefied flow regime. Also, a technique is used to extract approximate body-axis aerodynamic coefficients from the flight data. Comparisons of the rarefied transition flow aerodynamic behavior between the two sets of flight data indicate differences, primarily in the free-molecule flow coefficients; i.e. STS-7 shows a free-molecule flow behavior which correlates with diffuse surface reflection conditions, while STS-6 does not. The data have also been used to estimate the density profiles in the atmosphere. The atmospheric density is generated from 60 to 160 km from each flight. The density profiles produced have a primary wave structure and differences are observed between the two sets of flight data. A new rarefied transitional flow aerodynamic bridging formula has been generated from the flight data. Comparisons with the flight bridging formula and existing Monte Carlo and wind-tunnel data are made.

Blanchard, R. C.↗

NASA NTRS1986

Time dependent chemistry in dense molecular clouds. III - Infrared band cross sections of molecules in the solid state at 10 K

Thin film transmission infrared spectra and a list of integrated absorbance values (band strengths) of bands in the 2.5 to 20 micron range of various molecular solids deposited on a CsI window cooled to 10 K are presented. These solids include molecules known or suspected to be present on interstellar grains such as H2O, CO, NH3 and CH4 and mixtures of these molecules as well as various hydrocarbons. The method is described by which the absorbance values derived can be used to estimate column densities of species adsorbed on interstellar grains and other solids associated with celestial IR sources.

Dhendecourt, L. B.↗

NASA NTRS1986

An improved rocket ozonesonde (ROCOZ-A). II - Preparation of stratospheric ozone profiles

The ROCOZ-A radiometer measures ozone by long pathlength photometry in the stratosphere and lower mesosphere. After a rocket launch to an apogee of 70 km, the instrument measures the solar ultraviolet irradiance over its four filter wavelengths as it descends on a parachute. The fundamental values from ROCOZ-A are ozone overburdens versus radar altitude from 53 to 20 km. The slope of these values gives ozone number density. At one standard deviation the repeatability of the ozone overburden measurements averages 2.4 percent. For ozone number density the repeatability averages 3.2 percent with a significant increase at altitudes below the ozone number density maximum. The accuracy limits for overburden and number density are estimated at 5-7 percent. With auxiliary measurements of pressure and temperature, ozone results are also produced in terms of ozone mixing ratio, albeit with a slight broadening of the estimated accuracy limits. The vertical response of ROCOZ-A ozone measurements (full width at half maximum) is 4 km. The assembly of ROCOZ-A profiles can be used to compare with measurements from each of the current NASA and NOAA satellite ozone instruments. In addition, the repeatability of ROCOZ-A allows the use of this instrument as a transfer standard between satellite instruments with different fundamental ozone measurements.

Barnes, Robert A.↗