The Local Group galaxies constitute a fundamental step in the definition of
cosmic distance scale. Therefore, obtaining accurate distance determinations to
the galaxies in the Local Group, and notably to the Andromeda Galaxy (M31), is
essential to determining the age and evolution of the Universe. With this
ultimate goal in mind, we started a project to use eclipsing binaries as
distance indicators to M31. Eclipsing binaries have been proved to yield direct
and precise distances that are essentially assumption free. To do so,
high-quality photometric and spectroscopic data are needed. As a first step in
the project, broad band photometry (in Johnson B and V) has been obtained in a
region (34'x34') at the North-Eastern quadrant of the galaxy over 5 years. The
data, containing more than 250 observations per filter, have been reduced by
means of the so-called difference image analysis technique and the DAOPHOT
program. A catalog with 236238 objects with photometry in both B and V
passbands has been obtained. The catalog is the deepest (V<25.5 mag) obtained
so far in the studied region and contains 3964 identified variable stars, with
437 eclipsing binaries and 416 Cepheids. The most suitable eclipsing binary
candidates for distance determination have been selected according to their
brightness and from the modelling of the obtained light curves. The resulting
sample includes 24 targets with photometric errors around 0.01 mag. Detailed
analysis (including spectroscopy) of some 5-10 of these eclipsing systems
should result in a distance determination to M31 with a relative uncertainty of
2-3% and essentially free from systematic errors, thus representing the most
accurate and reliable determination to date.Comment: 12 pages, 9 figures; accepted for publication in A&A; see electronic
tables and full resolution images at
http://www.am.ub.es/~fvilarde/download/A+A
