GROUND-BASED HIGH SENSITIVITY RADIO ASTRONOMY AT DECAMETER WAVELENGTHS

51DESPA, CNRS/Observatoire de Paris, F-92195 Meudon, France2Institute of RadioAstronomy, Krasnoznamennaya 4, Kharkov 310002, Ukraine3Space Research Institute, Halbaerthgasse 1, Graz A-8010, Austria4Station de RadioAstronomie de Nancay, USR B704, Observatoire de Paris, 18 Nancay, France5ARPEGES, CNRS/Observatoire de Paris, F-92195 Meudon, FranceAbstractThe decameter wave radio spectrum (~10-50 MHz) suffers a very high pollution by man-made interference. However, it is a range well-suited to the search for exoplanets and thestudy of planetary (especially Saturnian) lightning, provided that very high sensitivity (~1Jansky) is available at high time resolution (0.1-1 second). Such conditions require a verylarge decameter radiotelescope and a broad, clean frequency band of observation. Thelatter can be achieved only through the use of a broadband multichannel-type receivingsystem, efficient data processing techniques for eliminating interference, and selectionand integration of non-polluted frequency channels. This processing is then followed byan algorithm performing bursts detection and measuring their significance. Theserequirements have been met with the installation of an Acousto-Optical Spectrograph atthe giant Ukrainian radiotelescope UTR-2, and four observations campaigns of Jupiter,Saturn, and the environment of nearby stars (including 51 Peg and 47 UMa) have beenperformed in 1995-96. The scientific objectives, observation techniques, instrumentation,data processing and first results of these studies, as well as simulation results, arepresented here. The sensitivity achieved (3-6 Jansky with 60-100 msec integration time)is promising and should allow for planetary lightning detection and subsequentmonitoring. Ground-based search for exoplanets at decameter wavelengths is shown tobe a realistic program for stars closer than ~25 parsecs.