The light-curve of microlensing event EROS-BLG-2000-5

Schematic representation of the lightcurve of the EROS-BLG-2000-5 microlensing event. It represents the changing brightness of a background star, as its light is being amplified by a binary gravitational lens that passes the line-of-sight from the Earth to the star. The ordinate indicates the factor by which the intensity increases during the various phases of the lensing event, as compared to the normal brightness of the star. The moment of the second "caustic crossing" is indicated, during which the image of the star is substantially brighter. Spectral observations were made with the VLT at the times indicated by arrows.