Eugene E. Epstein

Saturn's rings: 3-mm observations and derived properties

Abstract We have used 3-mm Saturn observations, obtained from 1965 through 1977 and with Jupiter as a reference, to derive a ring brightness temperature of 18 ± 8°K. Thebrightness temperature of the disk of Saturn is 156 ± 9° K. Part of the ring brightness (≈6†K) may be accounted for as disk emission which is scattered from the rings; the remainder (12 ± 8° K we attributed to ring particle thermal emission. Because this thermal component brightness temperatures is so much less than the particle physical temperature, limits are placed on the mean size and composition of the ring particles. In particular, as found by others, the particles cannot be rocky, but must be either metallic or composed of extremely low-loss dielectric material such as water ice. If the particles are pure water ice, for example, then a simple slab model and a multiple-scattering model both give upper limits to the particle sizes of ≈ 1 m, a value three times smaller than previously available. The multiple-scattering model gives a particle single-scattering albedo at 3 mm of 0.83±0.13.

Mars, Jupiter, Saturn, and Uranus: 3.3-mm brightness temperatures and a search for variations with time or phase angle

Abstract Extensive 3.3-mm observations yield disk-average brightness temperatures for Mars, Jupiter, Saturn, and Uranus of 180° ± 18°, 153° ± 1.25° ± 13°, and 105° ± 13° K (1 σ ), respectively. The values for the first three planets are corrected to heliocentric distances of 1.524, 5.203, and 9.540 a.u., respectively. Any variation of the temperature of Mars with phase angle is less than a few percent; this upper limit is consistent with an expected variation of ⪅3%. The measurements from mid-1965 to November 1969 contain no confirmed variations in the brightness temperatures of Jupiter and Saturn larger than ≈4 and ≈7%, respectively.

Observations of Galactic Carbon Monoxide Emission at 2.6 Millimeters.

Abstract : A wide variety of galactic sources have been observed at 2.6 mm (115271.2 MHz) to determine the extent and strength of interstellar 12C16O. Extended regions of CO emission were found in the direction of 32 HII regions and five supernova remnants. The CO emission was found to be larger in spatial extent than the 6-cm continuum HII emission and CO emission maxima appear to be related to continuum emission peaks and infrared sources in several sources. Except near optically dark nebulae, little CO emission was detected away from the galactic plane. Radial velocities of the CO emission are within 10/kms of the OH, HII (109 alpha), and H2CO velocities measured by other observers for the same sources. 13C16O was also measured in many of the stronger sources. The optical depths calculated for 12C16O range between 20 and 120, assuming the terrestrial value of 1/89 for the ratio of 13C/12C. For excitation temperatures in the range 10 to 50K, the calculated projected densities range from 10 to the 18th power to 2.5 x 10 to the 19th power molecules/sq cm. (Author)

Mars: A possible discrepancy between the radio spectrum and elementary theory

Abstract The available radio observations of Mars have been assessed. The radio spectrum does not turn up at short wavelengths, as predicted by elementary theory, but appears to be flat or perhaps slightly convex. Our ideas about the origin of the radio spectrum of Mars may require re-examination if future accurate and precise short millimeter-wave observations confirm the present spectrum.

Carbon Monoxide and Hydrogen Cyanide Millimeter-Wave Emission from Stars.

Thirty-four stars were surveyed for 2.6-mm CO emission and 49 for 3.4-mm HCN emission. The CO and HCN emission lines were detected in the directions of the carbon stars IRC+10216, IRC+30219, and possibly IRC+00382. The diameter of the CO source in the direction of IRC+10216 was measured to be in equilibrium 2- .3, which is larger than expected for this stellar source. The HCN emiasion source near IRC+10216 was less than ~40- in diameter. Extended CO emission sources were also found in the directions of the stars R Mon and T Tau. The infrared source IRC + 40091 (LkH alpha -- 101) near the H II region S222 was also found to have CO emission. (auth)

RADIO SOURCES: 3.3-mm FLUX AND VARIABILITY MEASUREMENTS.

Abstract : Graphical and tabular summaries of 3.3-mm (90-GHz) flux measurements of 35 discrete galactic and extragalactic sources are presented, including results of extensive monitoring of nine sources. Variability at 3.3-mm is certain for NGC 1068, NGC 1275, 3C120, 3C273, 3C279, VRO 42.22.01, and 3C454.3; repeated outbursts with time scales ranging from a week to several months have been observed for all of these except NGC 1068 and 3C454.3. (Author)

Mars: Subsurface properties from observed longitudinal variation of the 3.5-mm brightness temperature

Abstract Measurements at 3.5 mm of the disk-average brightness temperature of Mars during the 1978 opposition can be represented by T B (Mars, 3 5 mm, Jan/Feb 1978) = (The errors cited are from the internal scatter; the estimated absolute calibration uncertainty is 3%.) This longitudinal variation must be taken into account if Mars is to be used as a calibration source at millimeter wavelengths. The total range of the 3.5-mm variation is three to four times larger than both the 2.8-cm and 20-μm variations. This unexpected result can possibly be explained by subsurface scattering from rocks ≲1.5-cm radius.

Mercury - Thermal emission at radio wavelengths. I - 3.3- and 28-mm observed brightness temperatures and periodicities therein

Measurements of the thermal radio emission from Mercury at 3.3 mm were made on 103 days and at 28 mm on 113 days over a several-year interval. The data can be represented by TB(3.3 mm) = 359±4 + 147±6cos (φ + 17±2)°K,SD = 42°K,TB(28 mm) = 374±4 + 42±5 cos (φ + 36±7)°K,SD = 34°K where the statistical standard errors and deviations are indicated, TB is the brightness temperature, and phi; is the planetocentric phase angle. The estimated absolute calibration uncertainties are 7% (3.3 mm) and 5% (28 mm). Fitting with higher order harmonics of phi; or including the hermocentric longitude of the sub-Earth point does not improve the goodness of fit. Of the fits considered, the two data sets are best represented by multiterm harmonics as a function of time which include terms corresponding to several physically significant periods in the Earth-Mercury relationship. Summaries of measurements at 2.1, 3.1, 13.5, and 37.5 mm by other observers are included.

Mercury: observations of the 3.4-millimeter radio emission.

Observations of the 3.4-millimeter radio emission from Mercury during 1965 and 1966 yielded the following relationship between average brightness temperature TB of the disk and the planetocentric phase angle i: TB = 277 (� 12) + 97 (� 17) cos [i + 29 deg (� 10 deg)] �K The errors are statistical standard; the phase shift corresponds to a phase lag—that is, the maximum and minimum of insolation lag the maximum and minimum of planetary radiation.

Mercury: Anomalous Absence from the 3.4-Millimeter Radio Emission of Variation with Phase

Radio observations of Mercury at 3.4 millimeters from July to October 1965 showed, contrary to expectation, brightness temperatures of only about 200�K, even when major fractions of Mercurys illuminated hemisphere were observed. There was no significant variation with phase.