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The POINT-AGAPE Survey - I. The variable stars in M31

An, Jin H. ; Evans, N. W. ; Hewett, P. ; Baillon, P. ; Calchi Novati, S. ; Carr, B. J. ; Crézé, M. ; Giraud-Héraud, Y. ; Gould, A. ; Jetzer, Ph ; Kaplan, J. ; Kerins, E. ; Paulin-Henriksson, S. ; Smartt, S. J. ; Stalin, C. S. ; Tsapras, Y.

In: Monthly Notices of the Royal Astronomical Society, 2004, vol. 351, no. 3, p. 1071-1098

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    Titre
    • The POINT-AGAPE Survey - I. The variable stars in M31
    Auteur
    • An, Jin H.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Evans, N. W.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Hewett, P.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Baillon, P.. European Organization for Nuclear Research CERN, CH-1211 Genève 23, Switzerland
    • Calchi Novati, S.. Institut für Theoretische Physik, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • Carr, B. J.. Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS
    • Crézé, M.. Université Bretagne-Sud, Campus de Tohannic, BP 573, F-56017 Vannes Cedex, France
    • Giraud-Héraud, Y.. Laboratoire de Physique Corpusculaire et Cosmologie, Collège de France, 11 Place Marcelin Berthelot, F-75231 Paris, France
    • Gould, A.. Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
    • Jetzer, Ph. Institut für Theoretische Physik, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • Kaplan, J.. Laboratoire de Physique Corpusculaire et Cosmologie, Collège de France, 11 Place Marcelin Berthelot, F-75231 Paris, France
    • Kerins, E.. Astrophysics Research Institute, Liverpool John Moores University, 12 Quays House, Egerton Wharf, Birkenhead CH41 1LD
    • Paulin-Henriksson, S.. Laboratoire de Physique Corpusculaire et Cosmologie, Collège de France, 11 Place Marcelin Berthelot, F-75231 Paris, France
    • Smartt, S. J.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Stalin, C. S.. Laboratoire de Physique Corpusculaire et Cosmologie, Collège de France, 11 Place Marcelin Berthelot, F-75231 Paris, France
    • Tsapras, Y.. Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2004, vol. 351, no. 3, p. 1071-1098. Blackwell Publishing Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:304721
    Summary
    For the purposes of identifying microlensing events, the POINT-AGAPE collaboration has been monitoring the Andromeda galaxy (M31) for three seasons (1999-2001) with the Wide Field Camera on the Isaac Newton Telescope. In each season, data are taken for one hour per night for roughly 60 nights during the six months that M31 is visible. The two 33 × 33 arcmin2 fields of view straddle the central bulge, northwards and southwards. We have calculated the locations, periods and brightness of 35 414 variable stars in M31 as a by-product of the microlensing search. The variables are classified according to their period and brightness. Rough correspondences with classical types of variable star (such as Population I and II Cepheids, Miras and semiregular long-period variables) are established. The spatial distribution of Population I Cepheids is clearly associated with the spiral arms, while the central concentration of the Miras and long-period variables varies noticeably, the brighter and the shorter period Miras being much more centrally concentrated. A crucial role in the microlensing experiment is played by the asymmetry signal - the excess of events expected in the southern or more distant fields as measured against those in the northern or nearer fields. It was initially assumed that the variable star populations in M31 would be symmetric with respect to the major axis, and thus variable stars would not be a serious contaminant for measuring the microlensing asymmetry signal. We demonstrate that this assumption is not correct. All the variable star distributions are asymmetric primarily because of the effects of differential extinction associated with the dust lanes. The size and direction of the asymmetry of the variable stars is measured as a function of period and brightness. The implications of this discovery for the successful completion of the microlensing experiments towards M31 are discussed