Since the first discovery of a Jupiter-mass planet in 1995, more than 1000 planets are known to exist around main sequence stars. Most of the detection techniques are based on the radial velocity method which involves the measurement of the wobbling of the stars induced by the gravitational field of the orbiting giant planets. The second method , called "transit", can be used if a planet crosses in front of its parent star's disk; then the observed visual brightness of the star drops a small amount. The amount the star dims depends on the relative sizes of the star and the planet. This technique was successfully used by the Kepler spacecraft in the discover of about 1700 new planets.
The ITASEL program started 1999 with the search for water in 35 different targets by using a fast multichannel spectrometer, coupled to the 32 meters antenna of the Medicina Radioastronomical Station (S. Montebugnoli et al., Rev.Sci.Instrum.67, 365, 1995). The very high frequency and time resolution Fourier transform spectrometer employs an extremely powerful DSP (Digital Signal Processor) engine optimized for the FFT (Fast Fourier Transform) computations and it is able to perform transforms in a very short time. Its tremendous computation rate allows us to compute the FFT and the square magnitude on fly over an input bandwidth of 8 MHz, with an efficiency of 30-35 %. Our calculations have shown that observing in the beam switching mode integration times from 10 to 100 hours could be necessary for the closest stellar system since, unfortunately, the 32 m radiotelescope works only with single beam and single polarization feeds. As a consequence, due to the limited observing time available, a customized software was developed, to sum and average spectra taking into account that the doppler shifts of possible planets - due to both rotation and orbital velocities - are unknown.
At present the necessary software facilities to perform multiple beam observations have been developed, in order to exploit 100% of the antenna observing time allocated to the \project.
We carried out observations of:
- stellar regions where either cometary clouds have been discovered or planetary systems have been indirectly detected;
- peculiar stars, such as red and brown dwarfs with strong IR- radiation.
Up to now very faint possible transient signals with signal to noise ratios not higher than 3-4 have been tentatively identified and seem to be originated in a 2 arcmin region around 5 peculiar objects: Eps Eri, Lalande 21185, Tau Ceti, Gl581, Gl876. The most interesting seem to be:
Epsilon Eridani: only 10.8 ly away and among the 10 closest star systems to Earth. Recently a ring of dust or a cometary belt has been detected around it in the submillimeter region at the James Clerk Maxwell Telescope. Planetary formation around the star is probably complete since the stellar age is around 0.5-1.0 Gyr, and Earth-like planets are believed to form within 0.1 Gyr. This target represents the terrestrial conditions 4 Gyr ago when cometary bombardment is supposed to have ended and life started.
Lalande 21185: is one of the closest stars at 8.3 LY from the Sun. It is a small about 10 billion years old red dwarf and it could be surrounded by 3 giant planets. One at a distance of 2.2 AU from the star has been tentatively detected in 1996, but the discovery needs to be confirmed.