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Decameter wave planetary radio astronomy studies at ultra-high sensitivity and resolution (temporal & spectral) Jupiter and Saturn: dynamic spectroscopy and search for extrasolar planets

Exploitable results

The present Joint French-Austrian-Ukrainian Research Project was aimed to in-depth investigation of Jupiter's fast radio bursts, which origin is a key question for planetary radio emissions generation, and to the ground-based search for Saturn's lightning (discovered by Voyager 1 & 2, and which monitoring would be most interesting in view of the Cassini mission) and for exoplanets magnetospheric radio emissions. It has taken advantage of the very high sensitivity and time-frequency resolutions allowed by the UTR-2 Kharkov radiotelescope (world's largest at decameter wavelengths, with a 140000 m2 physical area) coupled to superfast, wideband digital receivers developed in Meudon-Nançay (Acousto-Opticai Spectrograph, or AOS) and Graz (Multi-Channel Spectrometer, or MCS). The receivers, interfaces, and associated computer hardware have been built/purchased (thanks to INTAS support) and installed at UTR-2 in April-May 1995. An archiving system (CDRom) has been added in fall 1996. Six observations campaigns involving scientists and engineers from the 3 participating countries have successfully used this hardware during the following year. Jovian millisecond ('S') bursts have been observed with time resolution of 2-5 msec and frequency resolution of 3-30 kHz, in the 10-30 MHz band. Simultaneous observations of S-bursts storms, in Graz and Nançay, provided complementary information. Hundreds of dynamic spectra with high signal/noise have been recorded and processed. The detailed burst morphology has been studied, in particular using automated pattern recognition/classification algorithms developed for that purpose in our teams. New S-bursts fine structure, sometimes scale-invariant and repeatable, has been identified. An operating model for the Jupiter-Io current system generating the S-component radio radiation has been proposed, as well as a generation scenario for the bursts. The former has been applied to the study of the large scale dynamics of Io's magnetic flux tube. Interpretation of fine structures in terms of chaotic components has been attempted. The effect of the Earth's ionosphere on Jovian emissions has been investigated. These investigations have been performed over several mutual visits, and led to 7 publications in refereed journals, 4 in books, and a dozen presentations in international meetings. An "Atlas of Jupiter Millisecond Radio Bursts" (2 Volumes) is in preparation. It should serve as a reference observational work for future theoretical studies. Detailed analyses and theoretical studies of bursts generation are continuing jointly, with the aim of explaining the complex time-frequency patterns observed. The large effective area of UTR-2 (calibrated as 20-50000 m2) and wide AOS band allow to reach the highest possible sensitivity at these (decameter) wavelengths, provided that man-made interference and terrestrial lightning are eliminated from the data. New methodologies and algorithms for interference elimination have been developed, taking advantage of the multi-beam capability of UTR-2 (which allows to perform simultaneous ON and OFF source observations in the same 10 MHz band). They allowed to reach a sensitivity ~ 1 Jansky (with δf~10 MHz and δtl sec), adequate for Saturn's lightning and/or exoplanet detection. The quiet interference environment of UTR-2 proves to be very favourable to these high sensitivity observations. Several presentations and reports have been made on these subjects, one paper published in a book, and further publications are in preparation. Technical studies have been initiated for still improving the quality of future high sensitivity observations, which could be extended to any star closer than 10-20 parsecs. High time-frequency resolution studies could also be extended to Solar radio bursts. This collaboration involved the direct participation of 6 French, 3 Austrian, and 4 Ukrainian scientists and engineers, plus collaborators and students. Information has been distributed among the team through an e-mailed newsletter. INTAS support both federated and enhanced the collaboration, and made it able to progress quickly on timely subjects. It is still very lively and expects long-term continuation.

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