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NASA NTRS1985

Images in the rocket ultraviolet - The stellar population in the central bulge of M31

Imagery of the bulge of M31 obtained with a rocket-borne telescope in two broad bands centered at 1460 A and 2380 A is discussed. The UV spatial profiles over a region about 200 arcsec wide are identical with those at visible wavelengths. The absence of detectable point sources indicates that main-sequence stars hotter than B0 V are not present in the bulge. It is suggested that the far-UV flux in old stellar populations originates in post-AGB stars. The UV flux from such stars is extremely sensitive to age and the physics of their previous mass loss.

Bohlin, R. C.↗
NASA NTRS1987

EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude

The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.

Schwartz, Daniel A.↗
NASA NTRS1986

The ionospheric extent of P/Halley from ground based operations during the 1985-1986 apparition

Spatial profiles of H2O(+) emission in the inner coma of P/Halley on 8 dates during the 1985 to 1986 apparition are presented. The profiles are derived from two dimensional CCD spectrograms taken with the spectrograph slit oriented along the cometary radius vector. The observations cover the range from 16 Oct. 1985 (r = 2.14 AU preperihelion) to 6 June 1986 (r = 2.14 AU postperihelion). The surface brightness profile of the 6198A H2O(+) emission line is calibrated in terms of the column density of H2O(+) ions. The profile from 14.4 Mar. 1986 is compared with the Giotto Ion Composition Experiment measurement of the shape of the H2O(+) space density profile. The ionosphere becomes larger and steeper in the sunward direction with an increasing water production rate.

Mccarthy, Patrick J.↗
NASA NTRS1986

Plasma wave turbulence in the strong coupling region at comet Giacobini-Zinner

Within 100,000 km of comet Giacobini-Zinner's nucleus, strong plasma wave turbulence was detected by the ICE electric and magnetic field wave instruments. The spatial profiles of the wave amplitudes are compared with measurements of the heavy ion fluxes of cometary origin, the plasma electron density, and the magnetic field strength. The general similarity of the wave and heavy ion profiles suggest that the waves might be generated by free energy in the pick-up ion distribution function. However, the expected parallel streaming instability of electrostatic modes generates waves with frequencies that are too low to explain the observations. The observed low frequency magnetic turbulence is plausibly explained by the lower hybrid loss-cone instability of heavy ions.

Coroniti, F. V.↗
NASA NTRS1985

Rocket observation of the ultraviolet spectrum of Comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on Feb. 26, 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 x 10 to the 29th/s and the volume mixing ratio of CO to H2O is 21 percent. The predicted brightness distribution from a radial outflow model with H2O and CO as parent molecules are in accordance with the measured spatial profiles of O I and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker C I emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3 percent of the water production rate is included in the model.

Woods, T. N.↗
NASA NTRS1986

The resolved layer of a collisionless, high beta, supercritical, quasi-perpendicular shock wave. I - Rankine-Hugoniot geometry, currents, and stationarity

Data collected by the ISEE dual-spacecraft mission (on November 7, 1977) on a slowly moving, supercritical, high-beta, quasi-perpendicular bow shock are presented, and the local geometry, spatial scales, and stationarity of this shock wave are assessed in a self-consistent Rankine-Hugoniot-constrained frame of reference. Included are spatial profiles of the ac and dc magnetic and electric fields, electron and proton fluid velocities, current densities, electron and proton number densities, temperatures, pressures, and partial densities of the reflected protons. The observed layer profile is shown to be nearly phase standing and one-dimensional in a Rankine-Hugoniot frame, empirically determined by the magnetofluid parameters outside the layer proper.

Scudder, J. D.↗
NASA NTRS1986

Rocket ultraviolet spectroscopy of comet Halley and abundance of carbon monoxide and carbon

Two far ultraviolet observations of comet Halley made on 26 February, 1986 and 13 March, 1986 with a sounding rocket experiment are reported. The observed CO spatial profiles can be modelled by a radial outflow model for a parent molecule and suggest that the CO is produced directly from the nucleus of the comet. Using the observed O I emission profile to deduce the H2O production rate, the abundance of CO relative to H2O is found to be 20 percent + or - 5 percent for the first flight and 17 percent + or - 4 percent for the second flight, making CO the second most abundant parent molecule in the coma. The derived production rate of atomic carbon is consistent with that expected from the photodissociation of carbon monoxide.

Woods, T. N.↗
NASA NTRS1988

Spatially resolved ultraviolet spectroscopy of the liner NGC 3998

Results of IUE observations of the Liner NGC 3998 are reported. Spatial structure in the long wavelength emission is apparent; the spatial profiles from the LWP line-by-line images show a two-component structure, with an unresolved central component superimposed on extended underlying emission. The LWP emission was separated into component spectra. The unresolved component spectrum is considerably flatter than the extended component spectrum, which is dominated by fairly late type stars (late F to early G). The unresolved component also shows strong C II) 2326 A and broad Mg II 2800 A emission.The width of the Mg II emission is 8600 km/sec, and its profile agrees quite well with the broad wings of the H alpha emission. The results support the idea that NGC 3998 may contain a dwarf Seyfert nucleus.

Reichert, G. A.↗
NASA NTRS1990

A near-infrared spectroscopic study of the starburst core of M82

Near-IR spectroscopy of the M82 starburst core is presented, including complete J, H, and K band spectra with a resolution of 0.0035-micron for the inner 60 pc of the galaxy. Also, spatial profiles along the starburst ridge are presented for Br-gamma, molecular hydrogen, and forbidden Fe II line fluxes. Emission from shocked molecular hydrogen is detected from the core of M82. The distribution of features across the starburst disk are mapped to study the relationships between spectral diagnostics. The observations are used to test the appropriateness of single-beam, aggregate models for studying the physical conditions in starbursts.

Lester, D. F.↗
NASA NTRS1990

The nonlinear evolution of magnetized solar filaments

Thermal instability driven by optically thin radiation is believed to initiate the formation of plasma filaments in the solar corona. The fact that filaments are observed generally to separate regions of opposite, line-of-sight, magnetic polarity in the underlying photosphere suggests that filament formation requires the presence of a highly sheared, local magnetic field. Two-dimensional, nonlinear, magnetohydrodynamic simulations of the local genesis and growth of solar filaments in a force-free, sheared, magnetic field were performed, and the evolution of generic perturbations possessing broad spatial profiles was traced. It was found that simulations of the evolution of initial random-noise perturbations produce filamentary plasma structures that exhibit densities and temperatures characteristic of observed solar filaments. Furthermore, in each of these simulations, the filament axis lies at a finite angle with respect to the local magnetic field, consistent with solar observations.

Sparks, L.↗
NASA NTRS1990

Distribution of gas in the inner comae of comets

In order to understand the physical and chemical processes which produce the observed spatial morphology of the cometary coma, it is necessary to analyze observational data with physically meaningful models. Thus, a coupled program of theoretical modeling and complementary observational data analysis was undertaken regarding the spatial distributions of neutral gases in the coma. More, specifically, the particular topics of interest are: (1) the theoretical modeling of the nonequilibrium dynamics of the inner coma with emphasis on the region of the coma from the transition from collisional fluid flow out to the free-flow region and on observable conditions in the coma (i.e., density, outflow speed, and temperature); and (2) the model analysis of an important set of long-slit CCD spectra of comets. The side-by-side development of models along with the observation and analysis of data is an important and integral part of this project. The scientific community has in hand valuable observational and in situ data regarding one comet, Halley. It is important to use Halley as the benchmark by which other remotely observed comet data can be understood. Therefore, the self-consistant analysis of data with appropriate models is of the utmost importance. The data analysis work includes the analysis of the spatial profiles of (OI), NH2, CN, and C2.

Combi, Michael↗
NASA NTRS1991

The P/Halley: Spatial distribution and scale lengths for C2, CN, NH2, and H2O

From P/Halley long slit spectroscopic exposures on 12 dates, extending from Oct. 1985 to May 1986, spatial profiles were obtained for emissions by C2, CN, NH2, and OI(1D). Haser model scale lengths were fitted to these data. The extended time coverage allowed the checking for consistency between the various dates. The time varying production rate of P/Halley severely affected the profiles after perihelion, which is shown in two profile sequences on adjacent dates. Because of the time varying production rate, it was not possible to obtain reliable Haser model scale lengths after perihelion. The pre-perihelion analysis yielded Haser model scale lengths of sufficient consistency that they can be used for production rate determinations, whenever it is necessary to extrapolate from observed column densities within finite observing apertures. Results of scale lengths reduced to 1 AU are given and discussed.

Fink, Uwe↗
NASA NTRS1991

The structure of Io's corona

A spatial profile of the distribution of sodium in Io's corona has been constructed using measurements obtained during satellite mutual eclipses. The data reveal a fairly symmetric corona whose density falls steeply from the surface out to 6 r(Io) and more slowly outside. An upper limit of 700 km is placed on the exobase altitude, but the observations do not constrain the surface density. Several theoretical models adequately match some traits of the corona, but none satisfies all the observations. No strong upstream/downstream asymmetry of the corona is observed, so it is unlikely that the corona is primarily generated by the impact of corotating ions into the trailing hemisphere.

Schneider, N. M.↗
NASA NTRS1991

Comet P/Halley - Spatial distributions and scale lengths for C2, CN, NH2, and H2O

Long-slit spectroscopic observations of Comet P/Halley on 12 dates between October 1985 and May 1986 were used to extract spatial profiles for C2, CN, NH2, and O I (1D) (which effectively map out the comet's H2O distribution), and Haser model scale lengths were fitted to these data. The preperihelion analysis yielded Haser model scale lengths of sufficient consistency that they could be used for the production rate determinations. It was found that the average parent scale lengths found for NH2 were consistent with photodissociation lifetimes for NH3 and confirm the dissociation chain NH3-NH2-NH.

Fink, Uwe↗
NASA NTRS1992

An evolving MHD vortex street model for quasi-periodic solar wind fluctuations

Magnetohydrodynamic (MHD) simulation are used to provide a dynamical basis for the 'vortex street' model of the quasi-periodic meridional flow observed by Voyager 2 in the outer heliosphere. Various observations suggest the existence near the current sheet at solar minimum, of a vorticity distribution of two opposite shear layers with an antisymmetric staggered velocity pattern due to structured high-speed wind surrounding low-speed equatorial flow. It is shown that this flow pattern leads to the formation of a highly stable vortex street through the nonlinear interaction of the two shear layers. Spatial profiles of various simulated parameters (velocity, density, meridional flow angle and the location of magnetic sector boundaries) and their relative locations in the quasi-steady vortex street are generally in good agreement with the observations.

Siregar, Edouard↗
NASA NTRS1992

Spectroscopic observations of comet Austin (1989c)

Longslit CCD spectra (lambda = 5100-6400 A, delta(lambda) approximately 3 A) were obtained with the Michigan-Dartmouth-MIT 1.3 meter telescope in May 1990 (r = 0.74 AU, delta = 0.50 AU). The spectra were reduced with the Interactive data Reduction and Analysis Facility (IRAF). Spectral extractions offset sunward and tailward from the nucleus were analyzed. Species identified in the spectra include the following: C2, NH2(10-0), NH2(9-0), H2O(+), and CO(+). Spatial extractions of rotational line intensities in the NH2(10-0) band extend approximately 10(exp 4.5) km from the nucleus. A fit of the vectorial model to the NH2(10-0) spatial profile is consistent with an NH3 parent molecule. The NH2 production rate and an ammonia to water abundance ratio, NH3/H2O approximately 3 percent, were derived. The ammonia abundance obtained for comet Austin is consistent with that found for several other comets and is indicative of comet formation under very homogeneous conditions.

Heyd, Rodney↗
NASA NTRS1993

The abundance of ammonia in Comet P/Halley derived from ultraviolet spectrophotometry of NH by ASTRON and IUE

From an analysis of the spatial profiles of both the NH and OH UV emissions observed by the ASTRON satellite, the ratio of ammonia-to-water production rates in Comet Halley on April 9, 1986 is derived and found to lie in the range of 0.44-0.94 percent. In order to compare this result with those based on both ground-based and in situ observations made on other dates during the 1985-1986 apparition of the comet, the IUE observational data base for December 1985 and March-April 1986 is used to evaluate the ratio of NH to OH column density in the IUE field of view and thus constrain the long-term behavior of this ratio. The IUE data base indicates that, to within a factor of 2, the ammonia-to-water production rate ratio is the same for a small sample of moderately bright comets observed recently.

Feldman, P. D.↗
NASA NTRS1993

Quasi-periodic transverse plasma flow associated with an evolving MHD vortex street in the outer heliosphere

We study a transverse plasma flow induced by the evolution of a Karman vortex street using a Chebyshev-Fourier spectral algorithm to solve both the compressible Navier-Stokes and MHD equations. The evolving vortex street is formed by the nonlinear interaction of two vortex sheets initially in equilibrium. We study spatial profiles of the total plasma velocity, the density, the meridional flow angle and the location of sector boundaries and find generally good agreement with Voyager 2 measurements of quasi-periodic transverse flow in the outer heliosphere. The pressure pulses associated with the meridional flows in the simulation are too small, although they are correctly located, and this may be due to the lack of any 'warp' in the current sheet in this model. A strong, flow-aligned magnetic field, such as would occur in the inner heliosphere, is shown to lead to weak effects that would be masked by the background interplanetary turbulence. We also study the plasma and magnetic transport resulting from the meridional flow and find that deficits of magnetic quantities do occur near the ecliptic. While the effect is relatively small, it is in general agreement with the most recent analysis of 'flux deficit' in the outer heliosphere.

Siregar, Edouard↗