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NASA NTRS1985

Far-infrared line observations of planetary nebulae. 1: The O 3 spectrum

Observations of the far-infrared fine structure lines of O III have been obtained for six planetary nebulae. The infrared measurements are combined with optical O III line fluxes to probe physical conditions in the gas. From the observed line intensity ratios, a simultaneous solution was obtained for electron temperature and density, as well as means of evaluating the importance of inhomogeneities. Densities determined from the far-infrared O III lines agree well density diagnostics from other ions, indicating a fairly homogeneous density in the emitting gas. Temperatures are determined separately from the O III 4363/5007 A and 5007 A/52 micron intensity ratios and compared. Systematically higher values are derived from the former ratio, which is expected from a nebula which is not isothermal. Allowance for the presence of temperature variations within these nebulae raises their derived oxygen abundances, determinations to be reconciled with the solar value.

Dinerstein, H. L.↗

NASA NTRS1984

Galaxy formation

Implications of the isotropy of the cosmic microwave background on large and small angular scales for galaxy formation are reviewed. In primeval adiabatic fluctuations, a universe dominated by cold, weakly interacting nonbaryonic matter, e.g., the massive photino is postulated. A possible signature of photino annihilation in our galactic halo involves production of cosmic ray antiprotons. If the density is near its closure value, it is necessary to invoke a biasing mechanism for suppressing galaxy formation throughout most of the universe in order to reconcile the dark matter density with the lower astronomical determinations of the mean cosmological density. A mechanism utilizing the onset of primordial massive star formation to strip gaseous protogalaxies is described. Only the densest, early collapsing systems form luminous galaxies.

Silk, J.↗

NASA NTRS1985

Chemical evolution of the Earth: Equilibrium or disequilibrium process?

To explain the apparent chemical incompatibility of the Earth's core and mantle or the disequilibrium process, various core forming mechanisms have been proposed, i.e., rapid disequilibrium sinking of molten iron, an oxidized core or protocore materials, and meteorite contamination of the upper mantle after separation from the core. Adopting concepts used in steady state thermodynamics, a method is devised for evaluating how elements should distribute stable in the Earth's interior for the present gradients of temperature, pressure, and gravitational acceleration. Thermochemical modeling gives useful insights into the nature of chemical evolution of the Earth without overly speculative assumptions. Further work must be done to reconcile siderophile elements, rare gases, and possible light elements in the outer core.

Sato, M.↗

NASA NTRS1985

Volatiles on satellites of the outer solar system

Molecules of cosmochemically abundant elements can act as volatiles and hence play a dominant role in the climatic and surficial evolution of solid bodies. Examples on terrestrial planets are H2O on Earth and H2O and CO2 on Mars. Analogous processes in the outer solar system focussing on CH4, its associated hydrocarbons, and N2 on Titan and Triton, the large moons of Saturn and Neptune were explored. A kilometer-deep C2H6-CH4 ocean was proposed for the surface of Titan to reconcile data on the lower atmosphere with understanding of the photochemical conversion of methane to heavier hydrocarbons. If such ocean exists, then it has dissolved in it an amount of N2 equal to the present atmospheric abundance. Since N2 contributes with CH4 a substantial greenhouse effect, the atmospheric physical and chemical characteristics are strongly coupled to those of the ocean, which change with time as methane is photolyzed in the stratosphere. Some relationship exists to the runaway greenhouse model for primordial Venus and the possible climatic implications of the buffering of Earth's atmospheric CO2 by the oceans. Two important diagnostics, measurable in Titan's atmosphere, of the conditions under which icy satellites formed are the abundances of noble gases and the CHd/CH4 radio. Both of these indicators have been altered during the evolution of Titan's surface-atmosphere system, the former by interaction with the ocean and the latter by progressive photolysis of methane into heavier hydrocarbons. The physical state and composition of volatiles on the surface of Triton is controversial, but plausibly could include CH4 N2 and perhaps CO. If condensed CH4 and N2 are widespread, their transformation to and from the vapor phase dominates the surface energy balance with sunlight. The extreme seasonal modulation of subsolar latitude on Triton is thus primarily expressed by volatile transport rather than large teperature changes, with possibly drastic observational consequences. The presence of two volatile species differing greatly in their vapor pressures make Triton a crude analog of Mars. Triton might be more appropriately regarded as a deep-freeze version of Titan.

Lunine, J. I.↗

NASA NTRS1985

Evidence for long-term variability in the ultra high energy photon flux from Cygnus X-3

A time-correlation analysis of atmospheric Cerenkov pulses by a wide-angle photomultiplier system was previously shown to have present in it a nonrandom component which seemed associated with the Right Ascension (RA) range approx. 20+or-04h. A recent examination of multi-muon events recorded by a photon-decay detector shows a similar time-dependent effect, closely matching the previous results, supporting the suggestion that the effect is of cosmic origin. However, even though Cyg. X-3 lies well inside the region of peak intensity, it does not seem possible to ascribe to it the whole effect, for the implied photon flux appears too large to be reconciled to various gamma-ray measurements of Cyg. X-3. The original data were subjected to a phase-histogram analysis and it as found that only 2.5% of overall recorded data are compatible with a phase-dependent emission from Cyg. X-3. Assuming these events to be gamma rays yields a detected flux of (2.6 + or - 0.3) x 10 to the minus 12th power gamma cm -2s-1 above 5 x 10 to the 14th power eV. Comparing this value with more recent ultra high energy (UHE) photon data from the same source, it is suggested that the available data generally favor a long-term reduction in the Cyg. X-3 inferred luminosity ( 10 to the 13th power eV) by a factor of (1.8 + or - 0.3) per year.

Bhat, C. L.↗

NASA NTRS1985

Energy dependence of cosmic ray composition above 10(15) GeV/nucleus

It is argued that above 10 to the 5th power GeV/nucleus, in the range where charge-resolved spectra have not yet been determined, the appropriate measures of equal-energy composition are 1nA and 1nA , the mean value and dispersion relative to the mean value and dispersion relative to the mean of 1nA, where A is the mass number. Experimental data which are sensitive to changes in 1nA with increasing energy are examined. It is found that, taken as a whole, they show no change (+ or 0.5) between 10 to the 5th power and 10 to the 6th power GeV, and a decrease of 1.5 + or - 0.5 between 10 to the 6th power and 10 to the 8th power GeV, with no further change + or - 0.5) above 10 to the 8th power GeV. Taken as a whole, the various indirect estimates of the absolute value of 1nA above 10 to the 5th power GeV/nucleus are also consistent with this pattern. For a wide range of astrophysically plausible composition models the value of the other measure, 1nA is insensitive to changes in 1nA . Because of this the existing data on 1nA can likewise easily be reconciled with this pattern.

Linsley, J.↗

NASA NTRS1985

On the importance of interstellar helium for the propagation of heavy cosmic rays

The influence of interstellar He on the fragmentation of heavy cosmic rays in the interstellar medium (ISM) has long been a controversial subject. While H-induced cross section data are now avialable over broad mass and energy ranges, little data for He-induced fragmentation exists. With the recent reports of accurate measurements of the secondary/primary ratios in cosmic rays and of H-induced cross sections the problem of including interstellar He in propagation calculations becomes even more critical. As is argued the escape lengths lambda e deduced from the B/C+) and Sc-Cr/Fe ratios cannot be reconciled within the frame of a simple leaky box model assuming the ISM composed of pure H. It is quite remarkable that the discrepancy is especially large in the GeV region where (1) secondary/primary ratios measured by several groups agree fairly well and (2) fragmentation cross sections have been recently measured with good accuracy.

Ferrando, P.↗

NASA NTRS1984

NGC 7213 - A key to the nature of liners?

New optical spectra of the nearby S0 galaxy NGC 7213 are analyzed. The observations are described and a brief overview of the spectrum is given. The subtraction of the stellar component is presented, and the measurement of various emission lines is discussed in detail. Important physical parameters are derived, including those pertaining to atomic data, line widths, physical conditions, geometry and kinematics, the Balmer decrement, and ultraviolet emission lines. The Seyfert characteristics of NGC 7213 are reviewed, and the galaxy's shock features are reconciled with photoionization models. The presented arguments may apply to classical liners as well. Theoretical models that can help explain the relationships discovered among the emission lines are examined.

Filippenko, A. V.↗

NASA NTRS1985

Megaregolith thickness, heat flow, and the bulk composition of the moon

Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25 percent higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83 percent of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) mantle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.

Rasmussen, K. L.↗

NASA NTRS1983

Large-scale motions of the tropics in observations and theory

Charney (1963) characterized the tropical atmosphere in terms of a superposition of large regions of nearly nondivergent circulations containing local subdomains, or 'fissures', of active convection and latent heating. Tropical wave evolution is then appropriately treated in terms of quasi-rotational waves, to the extent that the divergent contribution is small. An attempt is presently made to interpret recent tropical analyses in the aforementioned terms, suggesting extensions of the simplest quasi-rotational model capable of reconciling observations and theory. First GARP Global Experiment (FGGE) observations suggest that strongly divergent local tropical circulations are forced by latent heating and produce important direct modifications of the total wind field; after describing the extent to which the resulting field consists of divergent and rotational components in different analyses of the FGGE data, independent supporting documentation of the results in terms of heating estimates and rainfall observations are given.

Paegle, J.↗

NASA NTRS1985

Far-infrared line observations of planetary nebulae. I - The forbidden O III spectrum

Observations of the far-infrared fine structure lines of O III have been obtained for six planetary nebulae. The infrared measurements are combined with optical O III line fluxes to probe physical conditions in the gas. From the observed line intensity ratios, a simultaneous solution was obtained for electron temperature and density, as well as means of evaluating the importance of inhomogeneities. Densities determined from the far-infrared O III lines agree well with density diagnostics from other ions, indicating a fairly homogeneous density in the emitting gas. Temperatures are determined separately from the O III 4363/5007 A and 5007 A/52 micron intensity ratios and compared. Systematically higher values are derived from the former ratio, which is expected from a nebula which is not isothermal. Allowance for the presence of temperature variations within these nebulae raises their derived oxygen abundances, determinations to be reconciled with the solar value.

Dinerstein, H. L.↗

NASA NTRS1985

Recent heavy-particle decay in a matter-dominated universe

The cold matter scenario for galaxy formation solves the dark matter problem very nicely on small scales corresponding to galaxies and clusters of galaxies. It is, however, difficult to reconcile with a Universe with an Einstein-deSitter value of (UC OMEGA) = 1. Cold matter and (UC OMEGA) = 1 can be made compatible while retaining the feature that the Universe is matter dominated today. This is done by means of heavy (cold) particles whose decay subsequently leads to the unbinding of a large fraction of lighter clustered matter.

Olive, K. A.↗

NASA NTRS1985

Explanation of the inward displacement of Io's hot plasma torus and consequences for sputtering sources

Radial profiles of the ion density and flux-tube content in the Io torus have peak values inside Io's orbit, even though Io is the effective source of these ions. Formation of an inward peak constrains either the velocity distributions or source regions of sputtered neutrals. A further constraint is that the ionization of neutrals on trapped trajectories that return to Io's surface must be limited. A dominant sulphur source is most easily reconciled with these constraints.

Linker, J. A.↗

NASA NTRS1985

High-speed photometry of the eclipsing dwarf nova OY Carinae

High-speed photometry of the eclipsing dwarf nova OY Car in the quiescent state is presented. OY Car becomes highly reddened during eclipse, with minimum flux colours inconsistent with optically thick emission in the U and B bandpasses. Mass ratios in the range 6.5 to 12 are required to reconcile the eclipse structure with theoretical gas stream trajectories. Primary eclipse timings reveal a significant decrease in the orbital period and the duration of primary eclipse indicates the presence of a luminous ring about the white dwarf. The hotspot eclipse reveals a hotspot which is elongated along the rim of the accretion disc, with optical emission being non-uniformly distributed along the rim. The location of the hotspot in the accretion disc implies a disc radius larger than that of an inviscid disc, with variation in the position of the hotspot being consistent with a fixed stream trajectory.

Cook, M. C.↗

NASA NTRS1985

Extragalactic supernova remnants

Because the supernova remnants (SNRs) in other galaxies are at well-defined distances and because in many cases the reddening within extragalactic samples is more uniform than is the case for the Galactic SNR sample, extragalactic SNRs are fundamental to improving the understanding of SNR evolution. Here methods for identifying SNRs are reviewed and the current status of observational research is explored. The data do not unambiguously support the simple Sedov picture of SNR expansion, although it may be that the data can be reconciled with this picture if sufficient variation in initial conditions is allowed.

Long, K. S.↗

NASA NTRS1985

Star formation in the inner Galaxy - A far-infrared and radio study of two H II regions

Far-infrared and radio continuum maps have been made of two inner-Galaxy H II region complexes, G30.8-0.0 and G25.4-0.2, along with radio and molecular line measurements at selected positions. The far-IR emission from each region is dominated by two sources. For both G25.4 and G30.8, the distribution of the emission is similar to that of the radio emission, indicating that OB stars provide most of the heating. There is evidence that extinction plays an important role in G30.8, even in the far-IR. A near-IR point source has been detected in G30.8 at the position of peak far-IR color temperature. This source may be the ionizing star for the core of G30.8. Measurement of forbidden S III 9532 A from G25.4SE indicates that the extinction toward this source is very low, which is difficult to reconcile with previously determined distance measurements to this source.

Lester, D. F.↗

NASA NTRS1985

The coming revolution in planetology

Current ideas about the moon appear to be mistaken on two fundamental points. First, at least within certain large classes of lunar craters, internal origin (i.e., some form of volcanism) predominates over impact; this result raises questions about the reality of the 'era of violent bombardment'. Second, the origin of tektites by meteoritic impact on the earth cannot be reconciled with physical principles and is to be abandoned. The only viable alternative is origin by lunar volcanism, which implies the following: continuance of (rare) explosive lunar volcanism to the present time; existence of silicic lunar volcanism and of small patches of silicic rock at the lunar surface; a body of rock in the lunar interior, probably at great depth, which is closely similar to the earth's mantle and which contains billions of tons of volatiles, probably including hydrogen; and origin of the moon from the earth after the formation of the earth's core.

Okeefe, J. A.↗

NASA NTRS1985

The infrared size of IRc2/KL and its structure on an arcsecond scale

Small-aperture diffraction-limited scans of IRc2/KL at 7.8 and 12.5 microns are discussed. These scans, which were made at several position angles, spatially resolve the region within a 250 AU radius of this source, which is thought to be a newly formed luminous star undergoing heavy mass loss. IRc2 is found to have a pronounced elongation. The shape and orientation of this extended structure is similar to that seen on a larger scale in low-excitation molecular transitions, and is very similar to the distribution of H2O 'shell' masers. The size of the object may be reconciled with its dereddened blackbody temperature and total luminosity of 0.00001 solar luminosities (which is appropriate to OMC1) by the presence of small-scale structure. The observations thus support the idea that IRc2 is the primary luminosity source for OMC1. New astrometric measurements indicate that the 12.5 microns peak of IRc2 is coincident with the positions of the two bright SiO masers to within 0.3 arcsec.

Lester, D. F.↗