Jay Thor Bergstralh

The structure of the Uranian atmosphere: Constraints from the geometric albedo spectrum and H2 and CH4 line profiles

Constraints on the atmospheric structure of Uranus are derived from recently acquired, high-quality spectral observations [J. S. Neff, D. C. Humm, J. T. Bergstralh, A. L. Cochran, W. D. Cochran, E. S. Barker, and R. G. Tull (1984) Icarus 60, 221–235; J. T. Trauger and J. T. Bergstralh (1981) Bull. Amer. Astron. Soc. 13, 732; K. H. Baines, W. V. Schempp, and W. H. Smith (1983) Icarus 56, 534–542]. The analysis, based on detailed modeling of a broadband (7 A) geometric albedo spectrum from 3500 to 10,500 A and high-resolution (30 and 100 mA, respectively) observations of H2 4-0 quadrupole and 6818.9- A CH4 features, yields a family of models which parameterizes an upper tropospheric haze layer, a lower optically infinite cloud at a pressure level PCld, the cloud-level methane molar fraction, fCH4, and the mean ortho/para ratio in the visible atmosphere. Limits include 2.40 < PCld < 3.2 bars, 0.020 < fCH4 < 0.046, and 0.63 < feH2 < 0.95, where feH2 denotes the fraction of H2 in the equilibrium state. The haze optical depth at 6435 A is found to be 0.4 < τH (6435 A) < 1.0, in reasonable agreement with L.M. Traftons [(1976) Astrophys. J. 207, 1007–1024] determination but significantly less than that reported by K. H. Baines [(1983) Icarus 56, 543–559]. The single-scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A, reminiscent of UV-irradiated H2S ice crystals. These constraints are consistent with recent infrared and submillimeter and millimeter analyses. The analysis also agrees with the theoretical H2 quadrupole line strengths but conflicts with a number of reported laboratory measurements.

Photometric observations of jupiter at 2400 angstroms.

The photopolarimeter instrument on Voyager 2 was used to obtain a map of Jupiter at an effective wavelength of 2400 angstroms. Analysis of a typical north-south swath used to make this map shows strong absorption at high latitudes by a molecular or particulate constituent in the Jovian atmosphere. At 65� north latitude, the absorbing constituent extends to altitudes above the 50-millibar pressure level.

Infrared polar brightenings on Jupiter: IV. Spatial properties of methane emission

Abstract Polar “hot spots” observed on Jupiter at 7.8 μm with the NASA Infrared Telescope Facility at Mauna Kea, Hawaii, reveal different characteristics in the northern and southern hemispheres. The hot spot in the northern hemisphere is found to be fixed with respect to system III coordinates at 180±10° long and 60±10° lat. In contrast, the south polar hot spot is not fixed with respect to system III longitude; neither is it fixed with respect to the subsolar point or to Ios position. Additional analysis of the north polar hot spot, also with the help of Voyager I IRIS data, reveals that it is more extended in longitude than in latitude.

Spatially resolved absolute spectrophotometry of Saturn - 3390 to 8080 A

Abstract Absolute spectrophotometry of four regions on the visible disk of Saturn (north and south polar regions, equatorial band, south “temperate” region) from 3390 to 8080 A is reported. Spectral resolution is 10 A in the interval 3390–6055 A, and 20 A; aperture size is 1.92 arcsec. The explicit purpose of our observations was to provide ground-based photometric calibration for the Pioneer Saturn Imaging Photopolarimeter (IPP). We also compare our data with earlier spectrophotometric measurements of Saturn ( R.L. Younkin and G. Munch, 1963 ,Mem. Soc. Roy. Sci. Liege 7, 123–136; W.M. Irvine and A.P. Lane, 1971 ,Icarus 16, 10–26; T.B. McCord, T.V. Johnson, and J.H. Elias, 1971 ,Astrophys. J. 165, 413–424) and with the M. Podolak and R.EE. Danielson (1977) Icarus 30, 479–492) parameterization of “Axel Dust.” The latter reproduces the broad features but not the details of the observed spectral reflectivity (I/F). We find that large depths of clear molecular hydrogen (>14 km-am in the temperate regions) are needed to match the observed upturn in reflectivity shortward of 3800 A.

Photometry of 433 Eros from 0.65 to 2.2 μm

Abstract Lightcurves of 433 Eros are reported for 11 bandpasses ranging from 0.65 to 2.2 μm in wavelength. The relative spectral reflectance, R ( λ ), was not seen to vary during our observations. Eros has R (1.6 μ m) = 1.5 ± 0.1 and R (2.2 μ m) = 1.7 ± 0.1, where R ( λ ) is the spectral reflectance scaled to unity at λ = 0.56 μ m. This spectral reflectance is suggestive of a mixture of silicates and material with high infrared reflectance, perhaps a metallic phase such as meteoritic “iron”.

Absolute spectrophotometry of Neptune: 3390 to 7800 Å

Abstract Absolute spectrophotometry of Neptune from 3390 to 7800 A, with spectral resolution of 10 A in the interval 3390–6055 and 20 A in the interval 6055–7800 A, is reported. The results are compared with filter photometry ( Appleby, 1973 ; Wamsteker, 1973 ; Savage et al. , 1980 ) and with synthetic spectra computed on the basis of a parameterization proposed by Podolak and Danielson (1977) for aerosol scattering and absorption. A CH 4 /H 2 ratio of 1 × 10 −2 CH 4 −1 is derived for the convectively mixed part of Neptunes atmosphere, and constrains optical properties of hypothetical aerosol layers.

Infrared radiometry of Uranus and Neptune at 21 and 32 μm

Abstract Radiometric measurement of Uranus and Neptune near 21 and 32 μm have been made with filters with widths of 8 and 5 μm, respectively. The observations at 21 μm, made on 1985 June 19 at the NASA Infrared telescope facility at Mauna Kea, Hawaii, were calibrated against α Boo and corresponded to brightness temperatures of 54.1 ± 0.3 K for Uranus and 58.1 ± 0.3 K for Neptune. The observations at 32 μm were made on three nights: 1983 May 1 and 1984 May 30 and 31, also at the NASA IRTF. Calibrated against the Jovian satellites Callisto (J4) and Ganymede (J3), these measurements corresponded to brightness temperatures of 51.8 ± 1.5 K for Uranus and 55.6 ± 1.2 K for Neptune. The observations are consistent with higher-resolution studies and confirm the general decrease of brightness temperatures going from about 20 to 30 μm.