J. V. Radostitz

Submillimeter and millimeter observations of jupiter

We report narrowband photometry of the Jovian disk in 10 passbands covering the range from 0.35 to 3.3 mm wavelength. Absolute calibration was referenced to Mars. The derived brightness temperature spectrum is analyzed in the context of existing contraints on the atmospheric temperature structure and composition from ground-based studies at shorter wavelengths and from various spacecraft measurements. Our results for wavelengths between 0.35 and 0.45 mm suggest that the radiances can be matched by models which include NH3 ice particles which are between 30 and 100 μm in size, regardless of the scale height characterizing the cloud. It is difficult however, to model the relatively cool observations longward of 0.7 mm unless additional absorbers are assumed in the atmosphere or a different NH3 lineshape is assumed. If the absolute calibration scale were increased by 5%, the results would be fit by a clear atmosphere (or a small particle cloud) model, with no need to invoke additional absorption in the Jovian atmosphere.

Submillimeter and millimeter observations of Uranus and Neptune

We have made narrowband photometric measurements of Uranus and Neptune covering the wavelength range from 0.35 to 3.3 mm. The observations provide accurate comparative radiometry of these planets. Absolute calibration was referenced to Mars, and to Jupiter as a secondary standard. The results establish Uranus and Neptune as reliable secondary calibrators in their own right. We have combined our observations with other measurements made in the period 1978 through 1984 in the spectral range of 17 μm through 3 mm to form models for atmospheric temperature structure in the vertical range from 100 mbar to 8 bar. The simplest models imply that the tropospheres of both planets are consistent with “frozen” equilibrium H2 and a mixing ratio of CH4 of about 2% by volume in the deep atmosphere. There is some evidence in the Uranus data which implies the presence of discrete spectral lines. These could be due to CH4 pure rotational or dimer transitions or to minor constituents such as CO, which remain uncondensed even at the cold temperatures in the atmosphere of Uranus.

The Queen Mary College/University of Oregon photometer for submillimetre continuum observations

Recent advances in FIR detection and filter technology form the basis of a new multiband submillimetre photometer. The instrument provides a selection of filters to match the atmospheric transmission windows between 300 μm and 1.4mm wavelength, and uses a composite Ge bolometric detector cooled by 3He cryogenics to 0.35 K. It is designed primarily for use at the f/35 focus of the United Kingdom Infrared Telescope (UKIRT) and, in common with user instruments, is mounted on the UKIRT multiport photometer cage. This configuration allows use of the chopping secondary mirror for sky cancellation and of the TV optical system for either on- or off-axis guiding. Further, IR to millimetre wavelength coverage can be achieved in a single night by the use of several common focus photometers. Under good atmospheric conditions, the system achieves a noise-equivalent flux density (NEFD) of about at 1.1 mm, and about 10 Jy Hz− at 400μm.‡ These figures represent the best sensitivities yet reported at these wavelengths.

Multifrequency observations of blazars. II - The variability of the 1 micron to 2 MM continuum

The results of monitoring, over a period of two years, a sample of 12 blazars, in 11 wave bands between 1 micron and 2 mm are presented. All sources exhibit some variability, both in flux density and spectral shape. The infrared variability is consistent with repeated injections of reaccelerations of electrons, which subsequently suffer radiative losses. For OJ 287, 3C 279, and 3C 345, a decay and steepening of the infrared spectrum occurred as the submillimeter turnover evolved to lower frequencies, consistent with expansion of the emitting region. The peak flux, however, increased during this evolution. This behavior is inconsistent with most models for compact extragalactic sources, but it is naturally explained by shock waves traveling in an adiabatically expanding relativistic jet (Marscher and Gear, 1985).

Measurement of stratospheric HBr using high resolution far infrared spectroscopy

Far infrared spectral features of HBr have been observed in the stratospheric emission spectrum using a balloon borne high resolution Fourier transform spectrometer equipped with a high sensitivity detector specially designed for this purpose. The value of 1.6±0.6 parts per trillion in volume for the HBr mixing ratio has been retrieved, from the global‐fit analysis of 121 spectra, in the 25–36.5 km altitude range. The result is briefly compared with models and previous assessments.

The submillimeter spectra of the planets: Narrow-band photometry

Multicolor submillimeter observations of Jupiter, Saturn, Mars, and Uranus are reported. Narrow-band filters are used to define three passbands between 300 and 1600 μm to give accurate spectrophotometric data. A method for determining the atmospheric opacity from a single set of multicolor observations of a known source is shown to be consistent with secant plot data taken during very stable observing conditions. Such extinction data show that in the submillimeter region significant fluctuations in opacity occur over periods as short as 1 hr. At the time of observation the rings of Saturn were nearly edge-on and thus the disc brightness is determined without contribution from the ring emission. Comparisons with data obtained at earlier epochs give an estimate of the ring brightness as a function of wavelength. The disc emission spectra for Saturn, Jupiter, and Uranus are compared with various atmospheric models and other observations.

The brightness temperatures of Saturn and its rings at 39 microns

We have resolved the relative rings-to-disk brightness (specific intensity) of Saturn at 39 μm (δλ ≃ 8 μm) using the 224-cm telecscope at Mauna Kea Oservatory, and have also measured the total flux of Saturn relative to Jupiter in the same bandpass from the NASA Learjet Observatory. These two measurements, which were made in early 1975 with Saturns rings near maximum inclination (b′ ≃ 25°), determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiters absolute calibration make it possible to compare existing measurementsunambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 μm are all compatible (within 2σ) of a disk brightness temperature of 94°K, and do not agree with the radiative equilibrium models of Trafton; (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for λ ≲ 40 μm and (3) there is a decrease of ∼22% in the relative ring: disk brightness between effective wavelengths of 33.5 and 39 μm.

COSMIC-RAY BACKGROUNDS IN INFRARED BOLOMETERS

Cosmic-ray events are produced in infrared detectors by energy impulses which result from the ionization trails of fast charged particles. Model calculations are compared to the pulse-amplitude spectrum observed in a balloon flight from Palestine, Texas, at an altitude of 38 km. The results are useful for understanding cosmic-ray backgrounds which occur in all applications of high sensitivity bolometers.

Submillimeter observations of the asteroid 10 hygiea

We report the first successful ground-based observations of any asteroid at submillimeter wave-lengths. Observations of the asteroid 10 Hygiea at 370 and 770 μm are combined with observations in the near and thermal infrared (2.2, 10.6, and 21 μm) to study the thermal properties of Hygieas regolith. The “standard” (nonrotating) thermal model is consistent with the entire data set, although a rotating thermophysical model with a “lunarlike” thermal inertia cannot be ruled out.

Linear polarization variations modulo 5.6 days in HDE 226868

Results are reported for observations of variations in the linear polarization in HDE 226868 (the optical counterpart of Cyg X-1) made with a photoelastic polarimeter and a U-filter. The UV linear-polarization variations, as folded on the 5.6-day orbital period, are found to have amplitudes of 0.25% and position-angle changes of 2.7 deg. These results are shown to be consistent with the geometry and phasing required by the model of the binary system.