A New Search for Visual Aurorae on Jupiter.

Abstract

view Abstract Citations (6) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Search for Visual Aurorae on Jupiter. Dulk, George A. ; Eddy, John A. Abstract The nature of decametric radio emission from Jupiter and the known properties of its magnetic field suggest that energetic electrons frequently impinge on its upper atmosphere. These events, occurring at the time of decametric emission, should ionize atmospheric constituents and cause a visible recoml~ination emission spectrum. This Jupiter auroral emission has long been suspected but never observed. Past attempts to observe the effect in hydrogen-~ have mostly used filter monochromators, with bandpass 15-20 A, or low-dispersion spectrographs. The best previous search (Smi4~, Rodman, and Sloan. Astron. J. 68, 79, 1963) could have detected a 100 kilo- rayleigh aurora in HCL, had one occurred in their field of view. The recent finding that lo controls much of the radio emission (Bigg, Natttro 203, 10C8, 1964) enables one to predict the time and place of probable aurorae on Jupiter (Dulk, Science 148, 1585. 1965) and thus increases the chance of detection. Anroral activity is likely to occur on magnetic field lines connecting lo to Jupiter, at times and places favorable for detection several times per week, with duration 3 to 5 h. The authors have reinitiated the optical search for these events using the coude' spectrograph at the 84-in. telescope at the Kitt Peak National Observatory. Auroral emission expected is a narrow, weak perturbation in the reflected absorption lines, Doppler-shifted from line center by planetary rotation. With spectral resolution of 0.1 A, a 1.2 kilo- rayleigh aurora should be detectable in HCL, and approximately 10 kilorayleigh aurora elsewhere in the spectrum. Spectra were obtained on three favorable nights in November 1965 with negative results. We conclude that either no aurora brighter than 1.2 kilorayleigh was present or the spectrograph slit was incorrectly placed on the planet. Nearly concurrent filtergrams were obtained with a 5 A HCL interference filter which has a 1000 kilorayleigh auroral threshold. Publication: The Astronomical Journal Pub Date: February 1966 DOI: 10.1086/110070 Bibcode: 1966AJ.....71R.160D full text sources ADS |