The distance to the Andromeda galaxy from eclipsing binaries ^*,**,***

¹ Departament de Física, Enginyeria de Sistemes i Teoria del Senyal, Universitat d'Alacant, Apartat 99, 03080 Alacant, Spain e-mail: francesc.vilardell@ua.es
² Departament d'Astronomia i Meteorologia (ICC-IEEC), Universitat de Barcelona, c/ Martí i Franquès, 1, 08028 Barcelona, Spain e-mail: carme.jordi@am.ub.es
³ Institut de Ciències de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5, parell, 2a pl., 08193 Bellaterra, Spain e-mail: iribas@ice.csic.es
⁴ Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA e-mail: [edward.guinan;edward.fitzpatrick]@villanova.edu

Received: 15 September 2009
Accepted: 6 November 2009

Abstract

The cosmic distance scale largely depends on distance determinations to galaxies of the Local Group. In this sense, the Andromeda galaxy (M 31) is a key rung to better constrain the cosmic distance ladder. A project was started in 1999 to firmly establish a direct and accurate distance to M 31 using eclipsing binaries (EBs). After the determination of the first direct distance to M 31 from EBs, the second direct distance to an EB system is presented: M31V J00443610+4129194. Light and radial velocity curves were obtained and fitted to derive the masses and radii of the components. The acquired spectra were combined and disentangled to determine the temperature of the components. The analysis of the studied EB resulted in a distance determination to M 31 of = 24.30 ± 0.11 mag. This result, when combined with the previous distance determination to M 31, results in a distance modulus of = 24.36 ± 0.08 mag (744 ± 33 kpc), fully compatible with other distance determinations to M 31. With an error of only 4%, the obtained value firmly establishes the distance to this important galaxy and represents the fulfillment of the main goal of our project.