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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Optical spectrophotometry of Comet P/Giacobini-Zinner and emission profiles of H2O+

Two-dimensional CCD spectrograms were obtained of Comet P/Giacobini-Zinner (1984e) on five occasions between July and October 1985. Spatial emission profiles of H2O+ were extracted at 6198 angstroms (the strongest ionic line in the visible spectrum). This emission line traces the extent of the ion, or plasma, tail. The spectrographic slit was placed approximately along the trajectory of the ICE spacecraft on September 11, 1985; the resulting H2O+ profile has a full-width-half-maximum of about 5700 km, about three times that of the plasma density profile measured by ICE, and has a full-width-zero-intensity of about 30,000 km, very similar to the ICE values. H2O production rates for the comet are derived and compared with those of Comet P/Halley (1982i).

Strauss, M. A.↗
NASA NTRS1986

Optical rotation velocities and images of the spiral galaxy NGC 3198

H-alpha rotation velocities obtained from an echelle spectrogram to a radius of 2 arcmin for the spiral galaxy NGC 3198 agree well with the 21 cm rotation velocities of van Albada et al. (1985). The rotation curve is typical of Sc type galaxies in spite of NGC 3198's extended H I disk. From optical R and H-alpha-emission images, used to search for star-forming regions in the outer parts of this galaxy, several H-alpha knots are identified as far out as the Holmberg radius. With increasing radial distance out to 2 arcmin, the R-band surface brightness falls, the H-alpha is approximately constant, and the H I surface brightness rises.

Hunter, D. A.↗
NASA NTRS1986

Spectrum of sodiumlike selenium - Se XXIV

High-resolution spectra of Se XXIV have been obtained with a 3-m grazing-incidence spectrograph. Thin plastic foils coated with selenium were irradiated with four or eight beams of the OMEGA laser in a line-focus configuration. Spectrograms were obtained by viewing the plasma axially. Prominent in the spectra were the 3s-3p and 3p-3d transitions in the 150-240-A region and the transitions nl-(n + 1)l-prime with n = 3, 4 in the 24-80-A region. The energy levels and ionization limit derived from the measured wavelengths are also presented.

Brown, C. M.↗
NASA NTRS1986

Upwelling O(+) ion source characteristics

The characteristics of an upwelling ion source are discussed. A typical upwelling event is analyzed using Dynamic Explorer 1 satellite retarding ion mass spectrometer (RIMS) observations of the low-energy plasma, and energetic ion and local electromagnetic field observations. The RIMS spectrograms of the O(+) ion species, radial and axial head data for O(+), and spin plan O(+) distribution functions are examined. The features of the upwelling observed include: (1) transverse ion heating to temperature of 100,000 K, (2) large outward flows of O(+), (3) enhanced flow of H(+) and He (+), (4) moderately strong field-aligned current sheets, (5) an associated intense eastward convection channel, and (6) strong wave emissions in the range near and below the proton gyrofrequency. The association between the upwelling O(+) signature and auroral current is investigated. Plasma wave and electric field environments are studied and plasma flows and densities are derived. It is noted that the mechanism for ion heating which defines the source region for these polar ion outflows is related to field-aligned currents and an associated auroral convection channel or jet.

Moore, T. E.↗
NASA NTRS1986

Alfven-wave dissipation: A support mechanism for quiescent prominences

High resolution filtergrams or spectrograms of the main body of quiescent prominences often show a very vivid dynamical picture that cannot be reconciled with static models. Even if large differences exist between individual prominences in this respect, at least parts of the prominence are usually found to be in a 'choppy', turbulent state. Evidence for systematic flows are found in local regions in the prominence and also in the transition zone in the surroundings. These two regions are probably decoupled magnetically. Alfven waves are generally believed to be responsible for the heating in the upper chromosphere and corona (Hollweg 1986). Since evidence for the presence of Alfven-waves has also been found in the solar wind field, it is highly probable that such waves are generated in the convection zone of the sun and propagated outwards in the solar atmosphere wherever a proper magnetic field is present to carry the waves. The most basic magnetic formations in the solar atmosphere are simple loops. They occur all over the solar surface and cover a large range of magnetic field strengths. Loops with the strongest magnetic fields are found in active regions. It is to be expected that the Alfven-wave flux which is channelled into the loops from below, could show considerable variation both with heliocentric latitude, with time and locally between neighbouring loops. What happens when a magnetic loop is exposed to the appropriate Alfven-wave flux required to heat the upper solar atmosphere is examined.

Jensen, Eberhart↗
NASA NTRS1986

Comet P/Giacobini-Zinner electron and H2O column densities from ICE and ground-based observations

An H2O(+) emission profile extracted from an optical CCD spectrogram obtained during the ICE/Giacobini-Zinner encounter is compared to the electron density profile deduced from in-situ measurements by the ratio experiment aboard ICE. It is concluded that the electrons and the H2O(+) ions are distributed similarly 9600 km tailward from the cometary nucleus; that the ratio of number densities of H2O(+) ions to electrons is 1/4 at this point; and that the width of the plasma sheet is 16,000 km.

Meyer-Vernet, N.↗
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

Kitt Peak spectroscopy of P/Halley: October 1983-March 1985

Four low-resolution optical spectra of P/Halley obtained at heliocentric distances between 8.78 ad 4.83 AU using the cryogenic camera and R-C spectrograph on the 4 m Mayall reflector of Kitt Peak National Observatory are discussed. The resulting spectrogram shows a lack of the emission bands commonly seen in nearby cometary spectra. The optical color of Halley indicates that the comet is redder than the sun at less than 6000 A and slightly bluer above 6500 A. The substantial extent of the Halley dust coma is discussed, and an oxygen production rate of 3 x 10 to the 26th atoms/s at r = 4.83 AU is derived. These results are compared with those for other comets and those found for Halley by other authors.

Spinrad, H.↗
NASA NTRS1986

Far-ultraviolet fluorescence of carbon monoxide in the red giant Arcturus. II - Analysis of high-dispersion IUE spectra

Faint, diffuse emissions near 1380 A in deeply exposed IUE spectrograms of the red giant Arcturus very likely are associated with bands of the A-X fourth-positive system of carbon monoxide, fluoresced by multiplet UV2 of neutral oxygen near 1305 A. Numerical simulations indicate that the strength of the CO bands is exceedingly sensitive, in the best available one-dimensional model of the chromosphere of Arcturus, to a delicate balance between the rapid inward attenuation of the oxygen radiation field and the rapid outward decline of the molecular absorptivity. The fortuitous character of the overlap region in the single-component model argues that one should also consider the possibility that the pumping occurs in a highly inhomogeneous chromosphere, of the type proposed in previous studies of Arcturus based on observations of the infrared absorption bands of CO.

Ayres, T. R.↗
NASA NTRS1986

High-dispersion observations of alpha Bootis (K1 III) with the International Ultraviolet Explorer

Echelle spectrograms were obtained of the early-K red giant Arcturus in the far UV 1150-2000 A and middle-UV 2000-3200 A regions. Faint emission from forbidden Si II at 1892.0 A was detected. A surface flux of C IV was measured that was less than 1 percent of the solar surface flux. An observed faint spectral structure near 1380 A is believed due to the bands of the A-X fourth positive system of CO fluoresced by strong chromospheric emissions of the O I triplet. Constraints on the chromospheric structure, as evidenced by the fluorescent emissions and density-sensitive line ratios from multiplet UV lines of forbidden C II, are discussed.

Ayres, T. R.↗
NASA NTRS1987

The moderately interacting Algol-type eclipsing binary RY Geminorum

Ultraviolet spectra of the Algol-type semidetached system RY Geminorum, whose components can be described as A0 V and K0 IV, have been matched to the ultraviolet spectrum by Kurucz (1979) model atmospheres, and a best fit is found for T(eff) = 9150 K. Comparison with standard star spectra requires that this value be raised to 9400 K. The color excess of the system is determined to be no more than E(B-V) = 0.03 mag; the distance to the system is about 360 pc. The masses are approximately 2.36 and 0.38 solar masses, and the radii are 2.5 and 5.8 solar radii, respectively. The separation of the two centers is 26 solar radii. Evidence for a circumstellar line absorption is found in optical and ultraviolet spectrograms, and evidence is found in IUE spectra taken in partial eclipse for circumstellar emission lines of the type detected previously in the WS Serpentis stars and in several semidetected systems of the Algol type.

Plavec, Mirek J.↗
NASA NTRS1987

Comet P/Giacobini-Zinner electron and H2O(+) column densities from ICE and ground-based observations

An H2O(+) spatial mission profile, extracted from an optical CCD spectrogram obtained during the ICE/Giacobini-Zinner encounter, is compared to the electron-density profile that was deduced from in situ measurements by the radio experiment aboard ICE. The electron column density along a line of sight has two components, one from the spherically symmetric coma, and the second from a thin plasma sheet, whenever it is along the line of sight. The deduced electron column-density profile agrees well with the observed H2O(+) emission profile. It is concluded that the electrons and the H2O(+) ions are distributed similarly 9600 km tailward from the cometary nucleus, that the ratio of number densities of H2O(+) ions to electrons is about 1/4 at this point, and that the width of the plasma sheet is about 16,000 km.

Meyer-Vernet, N.↗
NASA NTRS1987

Optical region elemental abundance analyses of B and A stars. VII - The metallic-lined star 32 Aquarii

An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the metallic-lined (Am) star 32 Aquarii consistent with previous papers of this series. Its pattern of abundance anomalies is not identical with those of the hot Am stars although there are definite similarities. Changes of up to order 1 dex are foundly by comparison with the previous analysis by Smith. Slightly better agreement is found with the recent analyses of singly-ionized rare earth lines by Magazzu and Cowley. Results are also presented for a model selected on the basis of photometric indices according to the formula of Moon and Dworetsky.

Kocer, D.↗
NASA NTRS1988

Spatial extent of the plasma injection region in the cusp-magnetosheath interface

Using data from the high-altitude plasma instrument onboard the DE 1 spacecraft, the perpendicular (to the magnetic field) extent of the region of ion injection into the cusp has been estimated by measuring the energy dispersion of the ion V-shaped signatures seen on energy-time spectrograms. Three different passes were chosen based on the clarity of the V-shaped ion signatures. These studies indicate that the injection region has a dimension perpendicular to the magnetic field in the range D = 1000-6000 km at a radial distance of about 10 earth radii, in good agreement with reported diameters of flux transfer events (FTEs). Similar measurement of the energy dispersion of an electron V-shaped signature observed on one pass has yielded a parallel extent of the plasma injection region in the range D(parallel) = 100-350 km. The results lead to the suggestion that the plasma within an FTE travels down the field line as the field line convects antisunward, and may subsequently be observed in the polar cusp as a V-shaped signature.

Menietti, J. D.↗
NASA NTRS1988

Striated spectral activity in Jovian and Saturnian radio emission

Examination of high time resolution frequency-time spectrograms of radio emission measured near the Voyager 1 and 2 encounters with Jupiter reveals occasional striation patterns within the normally diffuse hectometric radiation. The patterns are characterized by distinctive banded structures of enhanced intensity meandering in frequency over time scales of minutes to tens of minutes. This banded form of striated spectral activity (SSA) has an occurrence probability of the order of 5 percent during the three weeks before and after Jupiter encounters. Plots of single 6-s frequency sweeps often exhibit a slow rise in intensity followed by a sharp drop-off in each band as frequency decreases. Banded SSA is often preceded or followed by chaotic SSA in which banding of the emission becomes discontinuous or unrecognizable, although the intensity modulation is still evident. Although SSA normally occurs in the frequency range of roughly 0.2-1.0 MHz, similar but longer-lasting patterns have been found occasionally in decametric emission above 10 MHz. Analogous modulation has also been observed in the Saturnian radio emission, suggesting that SSA may be a common feature intrinsic to the radio emission at both planets.

Thieman, James R.↗
NASA NTRS1988

The vertical structure of arch filament systems in solar emerging flux regions

The paper studies the vertical velocity of arch filaments in emerging flux regions by measuring their proper motion near the limb in H-alpha filtergrams and their radial velocity near the disk center in H-alpha spectrograms. Both show that arch filaments rise at a velocity between 10 and 15 km/s. The possible mechanisms producing this high velocity are discussed. None of them is satifactory, but it appears that the unloading of the arches by outflow must play a role. From the strength of H-alpha emission and D3 absorption, the temperature of arch filaments is estimated at 6000-15,000 K and the density at 10 to the 11th-12th/cu cm.

Chou, Dean-Yi↗
NASA NTRS1988

Absorption spectra of Fe I in the 1550-3215-A region

The high-dispersion absorption spectrum of Fe I is reported in the 1550-3215-A region. Included are wavelengths of about 3000 observed spectral features, improved spectral assignments, 248 new energy levels, and a value for the ionization potential of 63 737/cm obtained from extrapolation of Rydberg series. Improved wavelengths for several hundred V I and Ti I spectral lines determined on the same spectrograms as the iron data also are presented.

Brown, C. M.↗