Eclipsing binaries suitable for distance determination in the Andromeda galaxy

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 (M 31), is essential for determining the age and evolution of the Universe. With this ultimate goal in mind, we started a project of using eclipsing binaries as distance indicators to M 31. 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 were needed. As a first step in the project, broad band photometry (in Johnson B and V) was obtained in a region ($34'\times 34'$) in the north eastern quadrant of the galaxy over 5 years. The data, containing more than 250 observations per filter, were reduced by means of the so-called difference image analysis technique and the DAOPHOT program. A catalog with 236 238 objects with photometry in both B and V passbands was obtained. The catalog is the deepest ($V