Microlensing towards M 31 with MDM data

¹ Institute of Theoretical Physics, University of Zürich, Winterthurestrasse 190, 8057 Zürich, Switzerland
² Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, via S. Allende, 84081 Baronissi (Sa), and INFN Sez. di Napoli, Gruppo Collegato di Salerno, Italy
³ Physique Corpusculaire et Cosmologie, Collège de France, 11 place M. Berthelot, 75231 Paris, France
⁴ Department of Astronomy, Ohio State University, Columbus, OH 43210, USA

Corresponding author: S. Calchi Novati, novati@physik.unizh.ch

Received: 11 March 2003
Accepted: 18 April 2003

Abstract

We report the final analysis of a search for microlensing events in the direction of the Andromeda galaxy, which aimed to probe the MACHO composition of the M 31 halo using data collected during the 1998–1999 observational campaign at the MDM observatory. In a previous paper, we discussed the results from a first set of observations. Here, we deal with the complete data set, and we take advantage of some INT observations in the 1999–2000 seasons. This merging of data sets taken by different instruments turns out to be very useful, the study of the longer baseline available allowing us to test the uniqueness that is characteristic of microlensing events. As a result, all the candidate microlensing events previously reported turn out to be variable stars. We further discuss a selection based on different criteria, aimed at the detection of short-duration events. We find three candidates whose positions are consistent with self-lensing events, although the available data do not allow us to conclude unambiguously that they are due to microlensing.