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

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

2000-11-21

arxiv.org/abs/astro-ph/0011380v2

2001, ApJ Letters, 550, L173

Astronomy and Astrophysics

Astrophysics

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

Scientific paper

10.1086/319635

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.

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