Photometric constraints on microlens spectroscopy of EROS-BLG-2000-5

¹ CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette Cedex, France
² Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université de Paris-Sud, 91405 Orsay Cedex, France
³ Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ Collège de France, Physique Corpusculaire et Cosmologie, IN2P3 CNRS, 11 Pl. M. Berthelot, 75231 Paris Cedex, France
⁵ Universidad de la Serena, Facultad de Ciencias, Departamento de Fisica, Casilla 554, La Serena, Chile
⁶ Institut d'Astrophysique de Paris, INSU CNRS, 98bis boulevard Arago, 75014 Paris, France
⁷ Observatoire de Paris-Meudon DESPA, 92195 Meudon Cedex, France
⁸ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁹ Departments of Astronomy and Physics, Ohio State University, Columbus, OH 43210, USA
¹⁰ Observatoire de Marseille, 2 Pl. Le Verrier, 13248 Marseille Cedex 04, France

Corresponding author: J. F. Glicenstein, glicens@hep.saclay.cea.fr; gould@astronomy.ohio-state.edu

Received: 8 June 2001
Accepted: 8 August 2001

Abstract

We apply EROS photometric data to interpret previously published Keck and VLT spectra of the binary-microlens caustic-crossing event EROS-BLG-2000-5. We show that the VLT data imply that the outer of the limb of the K3-giant source is strongly in emission in Hα, in contradiction to available models of the photosphere. This conflict could be resolved if the integrated Hα emission from the chromosphere were equal to 8% of the integrated Hα absorption from the source as a whole. These conclusions regarding the extreme limb are almost completely model-independent. We also present a general method for using the photometric data to facilitate direct comparison between the atmospheric model and the spectroscopic data. While this method has some model-dependent features, it is fairly robust and can serve to guide the analysis of spectra while more detailed models of the lens geometry are being developed. In addition, we find that the color of the limb of the source (outer 5.5% by radius) is redder than the source as a whole, so that it has the color of a M0 giant.