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NASA NTRS1980

Physical processes in Jupiter's ring - Clues to its origin by Jove

It is shown that many of the observed properties of the Jovian ring can be explained by the presence of numerious small and unseen parent bodies, or 'mooms', residing within the ring; whose radii are less than 1 km. The small visible ring grains, which are destroyed in short times by sputtering and meteoroid erosion, are derived from these parent bodies largely through meteoroid impacts, and partly from Io's dust. Substantial orbit modification results from plasma drag, and the charge carried by the grains will influence their dynamics and may modify their shapes. It is concluded that the processes discussed, though present in other planetary ring systems, may be highlighted in Jupiter's ring because of its low optical depth and the small size of some of its particles. It is suggested that hidden reservoirs similar to the Jovian 'mooms' proposed may be present in the rings of Saturn and Uranus.

Burns, J. A.↗

NASA NTRS1981

Infrared studies of the S235 molecular cloud

Infrared observations from 7.8 to 200 microns have been obtained for the S235 molecular cloud. Far-infrared maps were obtained for a region of active star formation, as marked by the presence of compact H II regions, water masers, and compact near-infrared sources. The primary heating source for the far-infrared emission appears to be the compact H II region, S235A. Detailed examination of the gas energetics in the region supports the plausibility of the picture in which the gas is heated by collisions with warm dust grains. The ratio of far-infrared optical depth to (C-13)O column density is somewhat lower in this source than is commonly found. This effect may be caused by the presence of substantial (C-13)O in regions where the dust is not warm enough to emit substantial 50-100 micron radiation.

Evans, N. J., II↗

NASA NTRS1981

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO2 (180 ppm) and H2O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted (scale height, approximately 1 km) at higher altitudes. The total optical depth of the cloud region at or above 50 km is less than 0.17 at 1.35 cm wavelength. The SO2 upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO2 is more complex than given by the uniform mixing model.

Janssen, M. A.↗

NASA NTRS1981

The nature of the solar wind interaction with CO2/CO-dominated comets

The nature of the interaction of the solar wind with the ionospheres (field-free ion cavities) of comets with CO or CO2 as their dominant volatile species is considered and compared with the solar wind interaction with H2O-diominated comets. Calculations of the heliocentric variation of scale lengths defined as the nuclear distance at which the mean free path for ion-neutral collisions becomes equal to the nuclear distance, and the ion and neutral stand-off distances are presented for different modes of energy addition, nuclear radii and ionization time scales. Results indicate that whereas little activity can be expected from H2O-dominated comets at distances beyond 3 AU, COand CO2-dominated comets can be expected to be quite prolific at such distances. In contrast to H2O-dominated comets characterized by weak shocks, CO/CO2-dominated comet solar wind interactions are found to produce strong bow shocks within a specific heliocentric distance for the isothermal case of a CO-dominated comet, and a weak shock outside of this distance. In the general case, two types of cometary ionosphere transitions are found: a transition from strong to weak bow shock and from a compressible (soft) to an incompressible (hard) ionosphere, and a transition from a soft to a hard ionosphere with the bow shock remaining weak at a heliocentric distance dependant on atmospheric optical depth, bolometric albedo, nuclear radius, latent heat of sublimation of nuclear material, ionization time scale and type of heat addition. It is pointed out that the behavior of Comet Humason can be explained by solar wind interactions with a CO- or CO2-dominated comet.

Houpis, H. L. F.↗

NASA NTRS1981

Sunlight absorption by aerosols in Jupiter's upper atmosphere

The amount of sunlight deposited in the Jovian upper atmosphere is estimated from reflectivity measurements at 2400 A by the Voyager 2 Photopolarimeter experiment and at visible and near-IR wavelengths observed by Pioneer 10 and ground-based instruments. Zero to about one percent of the incident energy is absorbed at altitudes above the 100 mbar level in models with mean values for haze optical depth and single scattering albedo. Several percent of the incident energy could be absorbed, if limiting values are used, and if an additional absorbing layer is incorporated below the high altitude haze in Pioneer models. Maximum absorption occurs at the edge of the polar regions near + or - 65 deg latitude. Most of the absorbed energy is derived from visible and near-IR radiation rather than UV radiation.

West, R. A.↗

NASA NTRS1981

Implications of Titan's north-south brightness asymmetry

Voyager 1 images of Titan, when normalized to remove limb darkening, reveal an axially symmetric brightness pattern with significant north-south asymmetry. This interhemispheric contrast seems to be a response to seasonal solar heating variations resulting from Titan's inclined spin axis. The contrast significantly lags the solar forcing, indicating that its production involves the atmosphere well below the unit optical depth level. The contrast has a significant effect on Titan's disk-integrated brightness as seen from earth, and probably accounts for most of the observed long term variation, with solar UV variations accounting for the remainder.

Sromovsky, L. A.↗

NASA NTRS1981

The C IV 1550 profile in type 1 Seyfert galaxies

The paper presents C IV 1550 A line profiles for the type 1 Seyfert galaxies NGC 5548, Mrk 509, NGC 7469, and MCG-2-58-22. Several line broadening mechanisms and theoretical line profiles are considered, and random motion of discrete clouds is ruled out. A spherical ensemble of discrete clouds with steady outflow or inflow produces a logarithmic profile, but does not account for the highly extended wings. A spherical ensemble with ballistic outflow produces a profile of the first exponential integral function, and fits the observed profile to the continuum level. Although C IV profiles favor the ballistic model, both Mrk 509 and NGC 7469 have significant asymmetry, and Balmer lines with a higher optical depth show higher asymmetry and redshift than all four galaxies.

Wu, C.-C.↗

NASA NTRS1981

N-stream approximations to radiative transfer

Schuster's two-stream approximation (1905) is first derived from Chandrasekhar's radiative transfer equation (1950), and then extended to an arbitrary number of streams. The resulting technique for solving the transfer function similar to the discrete ordinate and spherical harmonic methods, is useful for modeling atmospheres with complicated phase functions and moderate optical depths. The resulting n coupled linear differential equations are simple and consume less computer time than other approximations, yet have the same required accuracy. The approximation is also flexible with respect to the choice of patch functions, and no approximations are made on the form of the phase function, other than its expansion into Legendre polynomials. A four-stream approximation is evaluated for a Henyey-Greenstein phase function with an asymmetry factor equal to 0.5.

Acquista, C.↗

NASA NTRS1981

Hard X-ray spectrum of Cygnus X-1

Long-term measurements of the hard X-ray spectrum from 3 keV to 8 MeV of the black-hole candidate Cygnus X-1 in its low state are reported. Observations were made from October 26 to November 18, 1977 with the A2 (Cosmic X-ray) and A4 (Hard X-ray and Low-Energy Gamma-Ray) experiments on board HEAO 1 in the spacecraft's scanning mode. The measured spectrum below 200 keV is found to agree well with previous spectra which have been fit by a model of the Compton scattering of optical or UV photons in a very hot plasma of electron temperature 32.4 keV and optical depth 3.9 or 1.6 for spherical or disk geometry, respectively. At energies above 300 keV, however, flux excess is observed which may be accounted for by a distribution of electron temperatures from 15 to about 100 keV.

Nolan, P. L.↗

NASA NTRS1981

Radio astronomy

A K-band reflected-wave ruby maser was used on the 64-meter (DSS-43) antenna at the Tidbinbilla Tracking Station, near Canberra, Australia. Spectral line observations were carried out near 22 GHz for water vapor sources and near 24 GHz for ammonia sources. The water vapor observations were made in the direction of known southern OH and H2O maser sources. All of the previously detected water line sources examined were detected. In addition, two new water vapor maser sources were discovered, G301.1+1.1and G308.9+0.1. The spectrum of G301.0+1.1 is presented six ammonia sources were found: G291.3-0.7, G305.4+0.2, G322.2+0.6, G327.3-0.5, G333.6-0.2, and G268.4-0.8. Spectra of two of these sources, G291.3-0.7 (RCW 57) and G305.4+0.2, are presented. Both show clearly the presence of the quadrupole splitting satellite lines that will allow the determination of NH3 optical depths in these clouds.

Shaffer, R. D.↗

NASA NTRS1981

SAM 2 measurements of the polar stratospheric aerosol, volume 1: October to April 1979

Weekly averages of Antarctic and Arctic stratospheric aerosol data as well as corresponding temperature profiles for the time and place of each stratospheric aerosol measurement (SAM) II measurement during the first 6 months of satellite flight are presented. From the aerosol extinction profile data, contours of aerosol extinction as a function of altitude and longitude or time are plotted. Aerosol optical depths are calculated for each week. Polar stratospheric clouds at altitudes of about 22 km were observed during the Arctic winter at various times and locations. A representative sample of the first 6 months of data to be used in atmospheric and climatic studies is outlined.

Mccormick, M. P.↗

NASA NTRS1981

Spectral atmospheric observations at Nantucket Island, May 7-14, 1981

An experiment was conducted by the National Langley Research Center to measure atmospheric optical conditions using a 10-channel solar spectral photometer system. This experiment was part of a larger series of multidisciplinary experiments performed in the area of Nantucket Shoals aimed at studying the dynamics of phytoplankton production processes. Analysis of the collected atmospheric data yield total and aerosol optical depths, transmittances, normalized sky radiance distributions, and total and sky irradiances. Results of this analysis may aid in atmospheric corrections of remote sensor data obtained by several sensors overflying the Nantucket Shoals area. Recommendations are presented concerning future experiments using the described solar photometer system and calibration and operational deficiencies uncovered during the experiment.

Talay, T. A.↗

NASA NTRS1981

Stratospheric aerosols

The current state of information on stratospheric aerosols is reviewed. Aerosol properties such as size, size distribution, composition, refractive index, number density, extinction, optical depth, and single scattering albedo are considered and generalized as much as possible to be representative of the global aerosol in times of volcanic and nonvolcanic (background) periods. Data are presented that show the global distribution of stratospheric aerosols as measured by the stratospheric aerosol and gas experiment (SAGE) satellite system for background and volcanic (post-Mount St. Helens) conditions. In addition, lidar and dustsonde data are presented that show the changes in stratospheric aerosol over an 8-year period.

Mccormick, M. P.↗

NASA NTRS1981

Geochemical and spectral characterization of naturally altered rock surfaces

The possibility of using the visible-near infrared region for compositional analysis of remotely sensed rock surfaces is studied. This would allow mapping rock type both on the Earth's surface and on other planetary surfaces. Reflectance spectroscopy, economic geology, optical depth determination, and X-ray diffraction mineralogy are discussed.

Chang, L. L. Y.↗

NASA NTRS1982

Is there any chlorine monoxide in the stratosphere?

A ground based search for the 856.50137/cm R(9.5) and for the 859.76765 R(12.5) transitions of stratospheric (Cl-35)O was made in the solar absorption mode using an infrared heterodyne spectrometer. Lines due to stratospheric HNO3 and tropospheric OCS were detected, at about 0.3% absorption levels. The expected lines of ClO in this same region were not detected, even though the optical depth of the ClO lines should be on the order of 0.2% using currently accepted ClO abundances. These infrared measurements suggest that stratospheric ClO is at least a factor of 7 less abundant than is indicated by indirect in situ fluorescence measurements, and the upper limit of 2.4x10 to the 13th power molecules/sq cm to the integrated column density of ClO is a factor of over 4 less than is indicted by microwave measurements. Results imply that the release of fluorocarbon precursors of ClO may be significantly less important for the destruction of stratospheric ozone than was previously thought.

Rogers, J. D.↗

NASA NTRS1982

Small scale structure in the interstellar medium: Orion's threadbare cloak

The interstellar medium in the central portion of the Orion Cloak dynamical feature was examined for evidence of fine structure. Four stars in the Ori OB I association, HD 37017, 37468, 37479, and 37776 bracket the stars in the lower belt region that were studied previously. Two are members of the sigma Ori subcluster. A lower limit to the scale inhomogeneity can be set using these at 0.1 pc, while on a scale of about 10 pc, the high velocity component of the second spectrum ions shows optical depth variation of more than a factor of 5. Neutral lines do not display the high velocity component. Some preliminary abundances are also given.

Shore, S. N.↗

NASA NTRS1981

One millimeter continuum observations of high redshift quasars

Upper limits to the one-millimeter continuum flux densities of the high redshift quasars B2 1225 + 31, Ton 490, and PHL 957 are presented. The upper limit to the power observed from these quasars at 1 mm is, on the average, one half of the observed power in the continuum at L-alpha. These observations are used to constrain the temperature of a hypothetical dust shell which reddens the quasar line and continuum emission by an extinction optical depth sufficient to account for the anomalously low L-alpha/H-alpha emission line ratio observed in each of these quasars. For the quasars studied, dust shell temperatures between 25 K and 50 to 95 K are prohibited by the present data. A dust shell at a temperature within this span reradiating all the power absorbed from the quasar ultraviolet continuum would produce a one-millimeter flux density greater than the measured upper limit. The average radius of the model dust shell cannot be between 70 kpc and 1 Mpc.

Ennis, D. J.↗

NASA NTRS1981

The high energy X-ray spectrum of 4U 0900-40 observed from OSO 8

The X-ray source 4U 0900-40 (= Vela XR-1) was observed with the high-energy X-ray spectrometer on OSO 8 for one week in 1976 and three weeks in 1978. Spectra of the source are presented above 16 keV. No systematic difference exists between the X-ray eclipse centers and the eclipse centers predicted from optical ephermerides. Short period intrinsic variability in the system's X-ray intensity may be related to changes in the Compton scattering optical depth in the system and does not require sporadic mass transfer via Roche lobe overflow. The 282 s modulation in the source's X-ray flux above 21 keV consists of two essentially similar pulses per period, most easily interpreted as arising from the two different magnetic poles of a rotating neutron star. The secondary appears to be a spherically accreting, magnetic neutron star.

Dolan, J. F.↗