SETI AT THE SPIN-FLIP LINE FREQUENCY OF POSITRONIUM

A directed search for extraterrestrial intelligence (SETI) has been ca rried out using the IRAM 30m telescope. Following a suggestion by Kard ashev (1979), the search was conducted at the spin-flip line of the li ghtest atom, namely positronium, at 203 GHz. Most of the 17 targets ar e mature stars with excess infrared radiation, which might be the wast e heat of a power-rich technological civilisation. The rest frame of t he cosmic background radiation was chosen as the velocity frame. The s pectral resolution used was 9.7 kHz. From the noise level, which was d etermined by the limited telescope time and weather conditions, the up per limit for the power of artificial omnidirectional transmitters at the positronium line frequency is of order 10(15) W. The relevance of this non-detection is discussed.