SIMBAD references

We analysed archival spectroscopic data of AM CVn taken with the William Herschel Telescope in 1996. In the literature two orbital periods for AM CVn are proposed. A clear S-wave in the Hei 4471, 4387 and 4143Å lines is revealed when the spectra are folded on the 1029-s period. No signature of this S-wave is seen when folded on 1051s. Doppler tomography of the line profiles shows a clear signature of the hotspot. Using this we can constrain the value of K₂ to lie between 210 and 280km.s^–1. Our work confirms the binary nature of AM CVn beyond any doubt, establishes 1028.73s as the true orbital period and supports the interpretation of AM CVn as a permanent superhump system.