SDSS J080449.49+161624.8: a peculiar AM CVn star from a colour-selected sample of candidates

We describe a spectroscopic survey designed to uncover an estimated ∼40 AM Canum Venaticorum (AM CVn) stars hiding in the photometric data base of the Sloan Digital Sky Survey. We have constructed a relatively small sample of about 1500 candidates based on a colour selection, which should contain the majority of all AM CVn binaries while remaining small enough that spectroscopic identification of the full sample is feasible. We present the first new AM CVn star discovered using this strategy, SDSS J080449.49+161624.8, the ultracompact binary nature of which is demonstrated using hightime-resolution spectroscopy obtained with the Magellan telescopes at Las Campanas Observatory, Chile. A kinematic ‘S-wave’ feature is observed on a period Porb = 44.5 ± 0.1 min, which we propose is the orbital period, although the present data cannot yet exclude its nearest