High dispersion spectroscopic observations of Venus near superior conjunction IV. Results for the carbon dioxide bands in the IV-N photographic region

Phase curves for the CO₂ bands at 7883, 7820, and 8689 Å are presented. While the weaker bands at 7820 and 7883 Å show a definite “inverse phase effect,” the band at 8689 Å shows a more normal phase curve; it also exhibited much larger day-to-day variations in the CO₂ abundance near superior conjunction in 1971. Because the variation of the phase curves with band strength is comparable to temporal variations on Venus, simultaneous observations of strong and weak bands are still needed to determine the dependence on band strength accurately.     

Photometric properties of outer planetary satellites

We present optical broadband photometry for the satellites J6, J7, J8, S7, S9, U3, U4, N1, and polarimetry for J6, obtained between 1970 and 1979. The outer Jovian satellites resemble C-type asteroids; J6 has a rotational lightcurve with period ～9.5 hr. The satellites beyond Jupiter also show C-like colors with the exception of S7 Hyperion. S9 Phoebe has a rotational lightcurve with period near either 11.25 or 21.1 hr. For U4 and N1 there is evidence for a lightcurve synchronous with the orbital revolution. The seven brighter Saturnian satellites show a regular relation between the ultraviolet dropoff and distance to the planet, probably related with differences in the rock component on their surfaces.     

Observations and interpretation of the close binary system CG Cyg

Photometric observations of the short-period (RS CVn-type) eclipsing binary system CG Cyg have been presented. Two sets of results, obtained from an analysis of theB, V andR light curves, represent ‘occultation’ and ‘transit’ solutions. The occultation solution is preferred as it gives a better fit to the colour curve. This hypothesis may also offer a more promising explanation of the observed peculiarities such as period changes and the light variation outside eclipses.     

Absolute dimensions of TT Hydrae

The photometric elements of the Algol type binary TT Hydrae derived by the authors from theirUBV observations during 1973–77 have been combined with the spectroscopic elements given by Sanford (1937) and Sahade and Cesco (1946) to obtain the absolute dimensions of the system. It is found that the spectroscopic orbital elements given by Sanford represent the evolutionary status of the secondary component better than those of Sahade and Cesco. The primary appears to be an Al v main sequence star of mass and radius ∼2.3R _⊙. The secondary fills its Roche lobe; it can be represented by a K0iii star of mass and radius ∼6.0R _⊙. Better spectroscopic data are needed for confirmation of these results.     

On the convective instability of finitely conducting viscous model chromosphere

The convective stability of a simple model chromosphere, consisting of protons, electrons and hydrogen atoms in the ground state, has been studied in the presence of a vertically upward uniform magnetic field to include the effects of FLR, Hall-currents, finite conductivity and ionization. The ionization in the chromosphere is collisional and the recombination is radiative. It is found that the Schwarzchild criterion should necessarily be satisfied for the stability together with the condition thatv > 2v ₀, where is kinematic viscosity andv ₀ is gyroviscosity. Some special cases have also been investigated.     

Surface texture of Vesta from optical polarimetry

Polarimetric, photometric, and reflectance spectroscopic properties of asteroid 44 Vesta are simulated in the laboratory by a preparation of eucrite Bereba consisting oof a broad mixture of particle sizes (mainly greater than 50-μm) mixed and partially coated with particles of size 10 μm and less. Coarse grains are necessary for producing the same albedo and a very fine dust coating is necessary for producing the same polarization inversion angle as observed for Vesta. There are less small grains and fine dust in this sample than in lunar soils. Photometrically, if coating a sphere, this sample shows a constant brightness on the sunward half of the observed hemisphere, the brightness being given on the other half by the Minnaert reciprocity principle. With such a photometric behavior, the global geometric albedo and the sub-Earth point geometric albedo differ by no more than 5%. The microscopic phase coefficient β is 0.021 magnitude per degree for the sample; the larger value, β = 0.025, observed telescopically for Vesta indicates that large-scale roughness is present on this asteroid.     

Saturn's rings: Particle composition and size distribution as constrained by observations at microwave wavelengths: II. Radio interferometric observations

The sizes, composition, and number of particles comprising the rings of Saturn may be meaningfully constrained by a combination of radar- and radio-astronomical observations. In a previous paper, we have discussed constraints obtained from radar observations. In this paper, we discuss the constraints imposed by complementary “passive” radio observations at similar wavelengths. First, we present theoretical models of the brightness of Saturn's rings at microwave wavelengths (0.34–21.0 cm), including both intrinsic ring emission and diffuse scattering by the rings of the planetary emission. The models are accurate simulations of the behavior of realistic ring particles and are parameterized only by particle composition and size distribution, and ring optical depth. Second, we have reanalyzed several previously existing sets of interferometric observations of the Saturn system at 0.83-, 3.71-, 6.0-, 11.1-, and 21.0-cm wavelengths. These observations all have spatial resolution sufficient to resolve the rings and planetary disk, and most have resolution sufficient to resolve the ring-occulted region of the disk as well. Using our ring models and a realistic model of the planetary brightness distribution, we are able to establish improved constraints on the properties of the rings. In particular, we find that: (a) the maximum optical depth in the rings is ～ 1.5 ± 0.3 referred to visible wavelengths; (b) a significant decrease in ring optical depth from λ3.7 to λ21.0 cm allows us to rule out the possibility that more than ～30% of the cross section of the rings is composed of particles larger than a meter or so; this assertion is essentially independent of uncertainties in particle adsorption coefficient; and (c) the ring particles cannot be primarily of silicate composition, independently of particle size, and the particles cannot be primarily smaller than ～0.1 cm, independently of composition.     

On the rate of ancient meteoroidal flux: Studies of the pre-mare crater population on the Moon

According to radiometric dating of lunar rocks, meteoroidal bombardment and accompanying cratering on the Moon were intensive in the first 0.7×10⁹ y, the so-calledterra stage. Recently the hypothesis of a terminal cataclysm has been gaining acceptance, meaning that a sharp increase in the bombardment followed by a steep decay occurred at the end of theterra stage.The purpose of this paper is to investigate possible variations in the intensity of the bombardment during theterra stage by analyzing the population of large (3–1000 km)terra craters and comparing it with results obtained by theoretical models. The proportion of fresh craters is specifically used.Observational data were obtained by studying the craters on an oldterra surface photographed by Zond 8 and/or covered by LTO and LM maps and by conducting a statistical study of theterra listed in the Lunar and Planetary Laboratory Catalog. Mathematical models were developed in such a way as to make them dimensionless, and as such applicable even without the knowledge of the physical constants and variables involved. Particularly powerful is the method of measuring time as multiples of the average lifetime of a crater of that size.The following conclusions and/or interpretations are reached. (1) A crater remains fresh for less than 20% of the average life of a crater of that size. (2) A condition of equilibrium (i.e., on the average, a new impact does not cause a net increase in the total number of craters) is reached or almost reached on lunarterrae. (3) The age of theterra surface is more than three average lifetimes of the 2 km to at least 20 km size craters (4) The observedterra crater population isnot the result of two cataclysms, one at the beginning of the stage and one at the end. (5) This population, however, could be the result of a constant or slowly decaying flux continuing until the end of the stage, when the terminal cataclysms occurred. This sequence of events cannot be proven or disproven. (6) If no terminal cataclysm occurred, then the meteoroidal flux during theterra stage was slowly decaying or constant. (7) The formation of all the large multi-ringed basins essentially contemporaneously is doubtful.     

Low-latitude thermal structure of Jupiter in the region 0.1–5 bars

The radiative heat flux from 0.1 to 10 bars is estimated on the basis of a “two-cloud” scattering model that fits available spectral data and Pioneer photometry. Deeper than a few bars, the flux is 4.5 W m^?2, compared with the 18.8 W m^?2 used in an earlier study by Trafton and Stone. A temperature profile is computed, with the H₂ pressure-induced opacity; the temperature at 1 bar is found to be 156°K, rather than the commonly accepted 170°K. An additional optical depth of unity at the 0.67-bar level could restore the conventional value; otherwise a considerably cooler atmosphere is a serious possibility.