The OGLE-II event sc5_2859: a classical nova outburst?

¹ CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: glicens@hep.saclay.cea.fr
² Max-Planck fuer Astronomie, Koenigsthul 17, 69117 Heidelberg, Germany
³ Department of Astronomy, Ohio State University, Columbus, OH 43210, USA
⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université de Paris-Sud, 91405 Orsay Cedex, France
⁶ Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁷ Institut d'Astrophysique de Paris, INSU CNRS, 98 bis Boulevard Arago, 75014 Paris, France
⁸ Osservatorio Astronomico di Padova, INAF, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁹ Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
¹⁰ European Southern Observatory (ESO), Casilla 19001, Santiago 19, Chile
¹¹ Physique Corpusculaire et Cosmologie, Collège de France, 11 Pl. M. Berthelot, 75231 Paris Cedex 5, France
¹² Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium
¹³ Observatoire de Marseille, 2 place Le Verrier, 13248 Marseille Cedex 04, France

Received: 3 August 2005
Accepted: 1 December 2005

Abstract

Context.The OGLE-II event sc5_2859 was previously identified as the third longest microlensing event ever observed.Aims.Additional photometric observations from the EROS (Expérience de Recherche d'Objets Sombres) survey and spectroscopic observations of the candidate star are used to test the microlensing hypothesis.Methods.The combined OGLE and EROS data provide a high quality coverage of the light curve. The colour of the sc5_2859 event is seen to change with time. A spectrum taken in 2003 exhibits a strong H_α emission line.Results.The additionnal data show that the OGLE-II sc5_2859 event is actually a classical nova outburst.