H-alpha Equivalent Width Variations across the Face of a Microlensed K Giant in the Galactic Bulge

Abstract

We present VLT FORS1 spectroscopy that temporally resolves the second caustic crossing of the Bulge K giant source of microlensing event EROS 2000-BLG-5, the first time this has been accomplished for several phases of a caustic transit. The ~1 angstrom H-alpha equivalent width of the source star increases slightly as the center of the star egresses the caustic and then plummets by 30% during the final limb crossing. These changes are not seen in contemporaneous spectra of control stars in the FORS1 slit, but are qualitatively consistent with expectations from stellar atmosphere models as the caustic differentially magnifies different portions of the stellar face of the target. Observations such as these in a variety of stellar lines are equivalent to atmospheric tomography and are expected to provide a direct test of stellar models.

arXiv comment15 pages, including 1 table and 4 figures. As accepted by ApJ Letters, vol 550

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• Full characterization of binary-lens event OGLE-2002-BLG-069 from PLANET observations
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• Probing Structures of Distant Extrasolar Planets with Microlensing
• Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlense H alpha line
• Applications of Microlensing to Stellar Astrophysics
• Photometric Constraints on Microlens Spectroscopy of EROS-BLG-2000-5
• The microlensing signatures of starspots
• Direct Lens Imaging of Galactic Bulge Microlensing Events
• The polarisation signature from microlensing of circumstellar envelopes in caustic crossing events
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• A New Method to Calibrate the Stellar Color/Surface-Brightness Relation
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• First Resolution of Microlensed Images of a Binary-Lens Event
• Probing MACHOs Toward the Galactic Bulge
• Angular Radii of Stars via Microlensing
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