2002A&A...386L..13I

We carried out optical observations of the field of the X-ray pulsator RX J0806.3+1527. A blue V=21.1 star was found to be the only object consistent with the X-ray position. VLT FORS spectra revealed a blue continuum with no intrinsic absorption lines. Broad (v∼1500km/s), low equivalent width (~-1/-6Å) emission lines from the HeII Pickering series were clearly detected. B, V and R time-resolved photometry revealed the presence of ∼15% pulsations at the ∼321s X-ray period, confirming the identification. These findings, together with the period stability and absence of any additional modulation in the 1min - 5hr period range, argue in favour of the orbital interpretation of the 321s pulsations. The most likely scenario is thus that RX J0806.3+1527 is a double degenerate system of the AM CVn class. This would make RX J0806.3+1527 the shortest orbital period binary currently known and one of the best candidates for gravitational wave detection.