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Nainital Microlensing Survey -- detection of short period Cepheids in the disk of M31

The discovery of large number of Cepheid variables in far-off galaxies offers a unique opportunity to determine the accurate distance of the host galaxy through their period-luminosity relation. The main aim of the present study is to identify short-period and relatively faint Cepheids in the crowded field of M31 disk which was observed as part of the Nainital Microlensing Survey. The Cousins R and I-band photometric observations were obtained with a 1-m telescope on more than 150 nights over the period between November 1998 to January 2002. The data was analysed using the pixel technique and the mean magnitudes of the Cepheids were determined by correlating their pixel fluxes with the corresponding PSF-fitted photometric magnitudes. Here, we report identification of 39 short-period Cepheid variables in the M31 disk. Most of the Cepheids are found with R (mean) ~ 20-21 mag and the dense phase coverage of our observations enabled us to identify Cepheids with periods as short as 3.4 days The frequency-period distribution of these Cepheids peaks at logP ~ 0.9 and 1.1 days.