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

We apply EROS photometric data to interpret previously published Keck and V LT spectra of the binary-microlens caustic-crossing event EROS-BLG-2000-5. We show that the VLT data imply that the outer similar to4% of the limb of the K3-giant source is strongly in emission in H alpha, in contradiction to available models of the photosphere. This conflict could be resolved if th e integrated H alpha emission from the chromosphere were equal to 8% of the integrated H alpha absorption from the source as a whole. These conclusion s regarding the extreme limb are almost completely model-independent. We al so present a general method for using the photometric data to facilitate di rect comparison between the atmospheric model and the spectroscopic data. W hile 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 t he lens geometry are being developed. In addition, we find that the color o f the limb of the source (outer 5.5% by radius) is Delta (V - I) similar to 0.37 redder than the source as a whole, so that it has the color of a M0 gi ant.