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NASA NTRS1984

He I 10830 emission in Seyfert galaxies and QSOs

He I line fluxes at 10830 A are reported for eight type-1 Seyfert galaxies, three QSOs and two type-2 Seyfert galaxies. The data are combined with He I line fluxes at 5876 A in order to obtain the ratio 10830/5876. The He I flux values resulting from this ratio are compared to fiducial values measured in gaseous nebulae. It is found that the values for gaseous nebulae are very similar to values observed in type-2 Seyfert galaxies, but are considerably larger than He I line flux values for type-1 Seyfert galaxies and QSOs. The data indicate the presence of high dust reddening and powerful optical depth effects in the type-2 Seyfert galaxies.

Levan, P. D.↗

NASA NTRS1984

Possible production by lightning of aerosols and trace gases in Titan's atmosphere

Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 x 10 to the -6th W/sq m can be expected. This value is much lower than that for earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C2N2 produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 0.01, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth.

Borucki, W. J.↗

NASA NTRS1984

Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment

The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas - the innermost satellite - the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous material near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.

Graps, A. L.↗

NASA NTRS1984

Line transfer in static and expanding spherical atmospheres

The integral-operator method is extended to line and continuum transfer calculations for static and expanding spherical radiating atmospheres. A relationship is defined between radiative transfer and the source function at particular optical depths. Linearized equations are developed for the mean intensity, monochromatic scattering, line transfer, and line transfer with absorption. Numerical solutions are obtained for each equation, as well as for background absorption and scattering, partial redistribution when the line source is frequency dependent, and line transfer in connection with the expansion velocity. Finally, a solution is found for spherical expansion in concert with partial redistribution and Doppler line broadening.

Avrett, E. H.↗

NASA NTRS1985

The stability of the oscillation motion of charged grains in the Saturnian ring system

A perturbation approach for the gravitoelectrodynamic forces encountered in the corotating plasma environment of Saturn is used to determine the stability of charged grains, given a random initial velocity. Attention is given to the implications of the Northrop and Hill (1982) and Mendis et al. (1982) results for the formation of the Saturnian ring system, and it is suggested that the marginal z stability radius at 1.5245 Saturn radii for Kepler-launched particles is due to an erosion process with ejecta of the order 0.05-0.5 microns, rather than that of the previously suggested plasma. The diffuseness of the Saturnian rings beyond the F ring is also explained in terms of instability, while a new critical radius for r instability is suggestd for the optical depth feature at 1.72 Saturn radii. The F ring is analyzed in detail.

Xu, R.-L.↗

NASA NTRS1984

How to find galaxies at high redshift

The UV and optical spectra presented for the blue star-forming galaxies Mrk 357, Mrk 496, and Mrk 26 have sufficiently large redshifts to make Lyman-alpha observations possible. Weak Lyman-alpha emission is observed in Mrk 357 and Mrk 469, with a flux value comparable to that of H-beta, and no detectable Lyman-alpha emission is detected in the case of Mrk 26. All three objects exhibit strong UV continuum emission, which is characteristic of hot stars, and although little evidence of dust is found, the observational constraints on extinction and neutral hydrogen column densities allow substantial reductions of the Lyman-alpha flux by dust absorption in conjunction with large line optical depths. These results imply that primeval galaxy detection calls for attention to be given to redshifted continuum emission from massive galaxies.

Hartmann, L. W.↗

NASA NTRS1985

Infrared spectra and interstellar reddening of anonymous type II OH/IR stars

Infrared positions and multicolor infrared photometry for a sample of type II OH/IR stars are reported. The infrared colors and 11.4-micron silicate optical depths of the confirmed sources in this group increase as a function of distance, suggesting that interstellar reddening must be taken into account in assessing their infrared energy distributions and physical characteristics.

Gehrz, R. D.↗

NASA NTRS1984

Formation of Saturn's spokes

The theoretical requirements of the Goertz and Morfill (1983) model of the formation of spokes in the rings of Saturn are analyzed. Consideration is given to model predictions of dust particle size distribution, the optical depth of the spokes, and the radial speed of spoke evolution. It is shown that the electrostatic levitation of singly charged dust particles would be sufficient to cause the spokes to form. The maximum formation time for spokes of more than 10,000 km radial length is estimated to be less than five minutes. Observations of the scattering properties of the spokes showed general agreement with the theoretical calculations.

Goertz, C. K.↗

NASA NTRS1983

Observation of El Chichon volcanic aerosols by the solar backscattered ultraviolet (SBUV) experiment

The Solar Backscatter Ultraviolet Experiment (SBUV) aboard the Nimbus-7 satellite identified large amounts of SO2 in the tropical stratosphere on April 15, 1982, 11 days after major eruption of the El Chichon volcano in southern Mexico. It is shown in the present study that the backscattered ultraviolet radiances measured by the SBUV experiment have been strongly affected by the presence of stratospheric volcanic cloud from the El Chichon eruptions. Both SO2 and aerosol amounts present in the volcanic cloud have been mapped on the basis of an analysis of the radiances measured by the SBUV and TOMS (Total Ozone Mapping Spectrometer) experiments. It is estimated that a volcanic cloud of optical depths as small as 0.03 can be detected using SBUV, provided the cloud reaches the middle atmosphere. Lower-altitude clouds have progressively smaller effects on the radiances as well as on the ozone profile derived from them and are therefore harder to detect.

Bhartia, P. K.↗

NASA NTRS1985

Hydrogen-deficient atmospheres for cool carbon stars

Motivated by recent work which hints at a possible deficiency of hydrogen in non-Mira N-type carbon stars and to further explore the parameter space of chemical composition, computations have been made of a series of hydrogen-deficient models for carbon stars. For these models Teff = 3000 K, and log g = 0.0. Solar abundances are used for all elements except for carbon (which is enhanced to give C/O = 1.05), hydrogen, and helium. As the fractional abundance of hydrogen is decreased, being replaced by helium, the temperature-optical depth relation is affected only slightly, but the temperature-pressure relation is changed. The most striking change in the emergent flux is the decrease of the H(-) peak at 1.65 micron compared with the blackbody peak at 1.00 micron.

Johnson, H. R.↗

NASA NTRS1985

Far-infrared observations of young clusters embedded in the R Coronae Australis and Rho Ophiuchi dark clouds

Multicolor far-infrared maps in two nearby dark clouds, R Coronae Australis and Rho Ophiuchi, have been made in order to investigate the individual contribution of low-mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low-mass stars has been detected in CrA and four in Rho Oph; their far-infrared luminosities range from 2 solar luminosities to 40 solar luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50 percent of the star's energy was radiated longward of 20 microns. Meaningful limits to the far-infrared luminosities of an additional 11 association members in CrA and two in Rho Oph were also obtained. The dust optical depth surrounding the star R CrA appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of these results for the cloud energetics and star formation efficiency in these two clouds are discussed.

Wilking, B. A.↗

NASA NTRS1984

Reflectance measurements from Landsat Thematic Mapper over rugged terrain

Spectral albedo measurements from the Landsat-4/5 Thematic Mapper require that spacecraft upwelling radiances be corrected for atmospheric absorption and scattering and for local surface illumination. A two-stream model is developed, with a lower boundary condition that varies with incidence angle. TM data must be registered to digital terrain data. Reflectance from points in shadows can be used to estimate optical depth. The primary application here is determination of the spectral albedo of snow. The TM is better-suited for this purpose than the MSS because of its larger dynamic range.

Dozier, J.↗

NASA NTRS1985

He II lambda 1640/lambda 4686 and Ly-alpha/H-beta ratios in the extraordinary Seyfert galaxy Markarian 359

The exceptionally narrow-lined Seyfert 1 galaxy Mrk 359 is ideally suited for determining reddening via the He II lambda 1640/lambda 4686 emission-line ratio. Here the validity of He II lines as a reddening indicator for quasars and Seyfert galaxies is reexamined and confirmed in the context of the most complete photoionization models available. In addition, lambda 1640 equivalent width measurements are shown to support previous contentions of substantial differences between observed and intrinsic quasar far-ultraviolet continua. Then IUE satellite and ground-based spectral data are presented, with the surprising result that both the lambda 1640/lambda 4686 and Ly-alpha/H-beta ratios do not differ greatly from case B recombination values in Mrk 359. This object is only slightly reddened, and it shows no evidence for extended, high-optical-depth H(+)/H(0) transition regions in the line-emitting gas. The very narrow lines and lack of deep transition regions and/or reddening may be related. In addition, Mrk 359 has low luminosity compared with most other Seyfert 1 galaxies, measured emission lines suggest an unusually high ionization parameter, and there is a hint of low nitrogen abundance. Further work is needed to examine possible relationships among all these peculiar properties.

Macalpine, G. M.↗

NASA NTRS1985

Variation in the stratospheric aerosol associated with the North Cyclonic Polar Vortex as measured by the SAM II satellite sensor

Optical depth data gathered by the stratospheric aerosol measurement (SAM II) satellite during the 1979-80 winter season are analyzed to study mean atmospheric motions. The spacecraft photometer yielded extinction rates over the Northern Hemisphere in the 8-30 km altitude interval. Filtering was performed to remove the effects of high clouds and polar stratospheric clouds. Free horizontal mixing was prevalent below 14 km, as was a systematic difference across the polar jet stream above that altitude. The aerosol declined in altitude as the winter progressed. The polar vortex is concluded to have a base at the 14 km altitude and an outer boundary which coincides with the jet stream axis. The model accords with atmospheric tracer measurements made during the open-air nuclear testing programs in the 1950s.

Kent, G. S.↗

NASA NTRS1985

Chlorine in dense interstellar clouds - The abundance of HCl in OMC-1

The first detection of a chlorine-bearing molecular species in the interstellar medium via emission from the J = 1-0 transition of HCl at 625.9 GHz toward OMC-1 is reported. The relative strengths, widths, and velocities of the resolved hyperfine components are consistent with moderate optical depth emission originating from dense, quiescent molecular cloud material. The overall emission strength implies a fractional abundance of f(HCl/H2) of about (0.5-5.0) x 10 to the -8th, depending on the density of the emitting region. This is approximately an order of magnitude below previous theoretical estimates and a factor of 3-30 below the cosmic abundance of Cl. Recent laboratory work suggests that the lowered fractional abundance of HCl is caused by a combination of depletion onto grains with gas-phase loss processes such as the reaction of HCl with C(+).

Blake, G. A.↗

NASA NTRS1985

The collisional dynamics of particulate disks

It is shown that the use of the Krook equation greatly simplifies the discussion of the collisional dynamics of particulate disks. Collisions are assumed to be inelastic from the outset. A simple heuristic argument is used to compute the effective collision rate in a disk of spherical particles with a power-law distribution of sizes. For Saturn's rings, the effective collision rate for momentum transport is substantially lower than that conventionally estimated on the basis of an observed optical depth at visual wavelengths. The closure of the vertically integrated set of moment equations without discarding the third-order moments at the outset is discussed, allowing for the possibility of a bent disk. In the limit that the collision frequency is much larger than the orbit frequency, the usual Navier-Stokes equations of viscous hydrodynamics for a thin disk are recovered with an explicit expression for the shear viscosity. The method is generalized to include the effects of gravitational scattering.

Shu, F. H.↗

NASA NTRS1985

Submillimeter observations of OH and CH in M42

The 2Pi(1/2) J = 3/2 to 1/2 transitions of OH at 163.12 and 163.40 microns have been detected, and upper limits have been obtained for the 2Pi(3/2) J = 3/2 to 1/2 transitions of CH at 149.09 and 149.39 microns, in observations of the Kleinmann-Low nebula of Orion. The results indicate emission from a gas cloud at a temperature of roughly 1000 K, having thickness of roughly 5 x 10 to the 14th cm with density about 7 million/cu cm and OH abundance of roughly 12 x 10 to the -6th. The OH column density is about 4 x 10 to the 16th/cu cm in the emitting regions. Optical depth effects play a major role in determining the relative strengths of the observed lines.

Viscuso, P. J.↗

NASA NTRS1985

Ozone, dust, smoke and humidity in nuclear winter

Recent correspondence on nuclear winter is commented on. Reasons are given for why the Tunguska meteor explosion may not be useful in calibrating the effects of a major nuclear exchange. The relationship between the optical depth of an aerosol cloud, the composition of the cloud, and its effect on sunlight intensity and climate are clarified. The significance of the Tambora eruption of 1815 and of historical fires for the nuclear winter theory are briefly discussed. The dispersion of smoke plumes from large fires is addressed, and water condensation and smoke scavenging are considered.

Turco, R. P.↗