Jason P. Aufdenberg, Antoine Mérand, Vincent du Foresto, Olivier Absil , Emmanuel Di Folco, Pierre Kervella , Stephen T. Ridgway, David H. Berger, Theo A. ten Brummelaar, Hal A. McAlister, Judit Sturmann, Lazslo Sturmann, and Nils H. Turner
INFRARED INTERFEROMETRIC GRAVITY DARKENING OBSERVATIONS OF VEGA WITH CHARA/FLUOR (Poster)

INFRARED INTERFEROMETRIC GRAVITY DARKENING OBSERVATIONS OF VEGA WITH CHARA/FLUOR

Jason P. Aufdenberg(1), Antoine Mérand(2), Vincent du Foresto(2), Olivier Absil (3), Emmanuel Di Folco(2), Pierre Kervella (2), Stephen T. Ridgway(1), David H. Berger(4), Theo A. ten Brummelaar(5), Hal A. McAlister(6), Judit Sturmann(5), Lazslo Sturmann(5), and Nils H. Turner(5)
(1)National Optical Astronomy Observatory
(2)LESIA, Observatoire de Paris-Meudon
(3)University of Liege
(4)University of Michigan
(5)CHARA Array, Mt. Wilson Observatory
(6)CHARA, 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 $\sim$91% of its angular break-up rate with an equatorial velocity of $\sim$275 km ${\rm s}^{-1}$. We find a polar effective temperature of $\sim$10150 K and a pole-to-equator effective temperature difference of $\sim$2300 K. 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.