first results from the pomme survey of m31

the pomme survey (pixel observations of m31 with megacam) monitored two fields in the disc of m31 using megacam at cfht over a timespan of 2.5 months in three filters (g´, r´, i´). covering a large fraction of the disc of m31, it yields an unprecedented view on cepheids, eclipsing binaries and microlensing events in m31. in this contribution we present the first results on the cepheid populations in m31. using difference imaging we detect more than 2500 cepheids in the period range from 2 to 80 days, making the catalogue the largest and most homogeneous database of m31 cepheids to date. the period distribution peaks at log p[day] ≈ 0.63. we confirm the presence of a second peak in the period distribution at log p[day] ≈ 1.13, consistent with previous findings on smaller samples, and which is also present in galactic cepheids, unlike those at the lower metallicities of the lmc. using the fourier parameters derived from light curve fitting we identify 200 first overtone pulsators among the pomme cepheids. on-going work will include the derivation of period-luminosity relations and the extension of the analysis to eclipsing binary systems, yielding an improved distance to m31 and tighter constraints on systematics affecting the period-colour-metallicity-luminosity relations.