AAS 207th Meeting, 8-12 January 2006
Session 82 Ground Based Optical Interferometry
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[82.03] Interferometric Gravity Darkening Observations of Vega with the CHARA Array

J. P. Aufdenberg (NOAO), A. Merand, V. Coude Foresto (LEISA), O. Absil (Univeristy of Liege), E. Di Folco, P. Kervella (LEISA), S. T. Ridgway (NOAO/NASA), J. Sturmann, L. Sturmann, T. A. ten Brummelaar, N. H. Turner, D. H. Berger (CHARA Array), H. A. McAlister (Georgia State University)

We have obtained high-precision interferometric measurements of the A0 V standard star Vega with the Center for High Angular Resolution Astronomy (CHARA) Array and the Fiber Linked Unit for Optical Recombination (FLUOR) beam combiner in the K' band at projected baselines between 103 m and 273 m. The measured squared visibility amplitudes beyond the first lobe are significantly weaker than expected for a slowly rotating star and provide strong evidence for the model of Vega as a rapidly rotating star viewed very nearly pole on. We have constructed a Roche-von Zeipel gravity-darkened model atmosphere which is in generally good agreement with both our interferometric data and archival spectrophotometry. Our model indicates Vega is rotating at ~92% of its angular break-up rate with an equatorial velocity of ~275 km s-1. We find a polar effective temperature of ~10150 K and a pole-to-equator effective temperature difference of ~2500 K, much larger than the ~300 K derived by Gulliver, Hill, and Adelman. Our model suggests that Vega's cool equatorial atmosphere may have significant convective flux and predicts a significantly cooler spectral energy distribution for Vega as seen by its surrounding debris disk.

This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology. The CHARA Array is operated by the Center for High Angular Resolution Astronomy with support from Georgia State University and the National Science Foundation, the Keck Foundation and the Packard Foundation.

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