Frank Scherb

Large-aperture [O I] 6300 Å photometry of comet Hale-Bopp: Implications for the photochemistry of OH

Large-aperture photometric observations of comet Hale-Bopp (C/1995 O1) in the forbidden red line of neutral oxygen ([O I] 6300 with the 150 mm dual-etalon spectrometer that comprises the Ae ) Fabry-Pec rot

Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus

A large database of sunlit Io [O I] 6300 A emission, acquired over the period 1990–1999, with extensive coverage of Io orbital phase angle ϕ and System III longitude λIII, exhibits significant long-term and short-term variations in [O I] 6300 A emission intensities. The long-term average intensity shows a clear dependence on λIII, which establishes conclusively that the emission is produced by the interaction between Ios atmosphere and the plasma torus. Two prominent average intensity maxima, 70° to 90° wide, are centered at λIII ≈ 130° and λIII ≈ 295°. A comparison of data from October 1998 with a three-dimensional plasma torus model, based upon electron impact excitation of atomic oxygen, suggests a basis for study of the torus interaction with Ios atmosphere. The observed short-term, erratic [O I] 6300 A intensity variations fluctuate ∼20–50% on a timescale of tens of minutes with less frequent fluctuations of a factor of ∼2. The most likely candidate to produce these fluctuations is a time-variable energy flux of field-aligned nonthermal electrons identified recently in Galileo plasma science data. If true, the short-term [O I] intensity fluctuations may be related to variable field-aligned currents driven by inward and outward torus plasma transport and/or transient high-latitude, field-aligned potential drops. A correlation between the intensity and emission line width indicates molecular dissociation may contribute significantly to the [O I] 6300 A emission. The nonthermal electron energy flux may produce O(1D) by electron impact dissociation of SO2 and SO, with the excess energy going into excitation of O and its kinetic energy. The [O I] 6300 A emission database establishes Io as a valuable probe of the torus, responding to local conditions at Ios position.

Observations of comet Kohoutek (1973f) with a ground-based Fabry-Perot spectrometer

Observations of H

Solar cycle variations of geocoronal Balmer α emission

alpha

Low-intensity Balmer emissions from the interstellar medium and geocorona.

, H

Spatial distribution of O(1D) from Comet Halley

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Variations in Optical S+ Emission from the Io Plasma Torus: Evidence for Quasi Periodicity

O

Comet Halley O(1D) and H2O production rates

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Measurements of [C I] Emission from Comet Hale-Bopp

, and O i emission lines from comet Kohoutek were made during a 2-month period around perihelion. Analyses of H

The Io sulfur torus in 1981

alpha