Circumstellar material in the Vega inner system revealed by CHARA/FLUOR

Context. Only a handful of debris disks have been imaged up to now. Due to the need for high dynamic range and high angular resolution, very little is known about the inner planetary region, where small amounts of warm dust are expected to be found. Aims. We investigate the close neighbourhood of Vega with the help of infrared stellar interferometry and estimate the integrated K-band flux originating from the central 8 AU of the debris disk. Methods. We performed precise visibility measurements at both short (similar to 30 m) and long (similar to 50 m) baselines with the FLUOR beamcombiner installed at the CHARA Array (Mt Wilson, California) in order to separately resolve the emissions from the extended debris disk ( short baselines) and from the stellar photosphere (long baselines). Results. After revising Vega's K-band angular diameter (theta(UD) = 3.202 +/- 0.005 mas), we show that a significant deficit in squared visibility (Delta V-2 = 1.88 +/- 0.34%) is detected at short baselines with respect to the best-fit uniform disk stellar model. This deficit can be either attributed to the presence of a low-mass stellar companion around Vega, or as the signature of the thermal and scattered emissions from the debris disk. We show that the presence of a close companion is highly unlikely, as well as other possible perturbations ( stellar morphology, calibration), and deduce that we have most probably detected the presence of dust in the close neighbourhood of Vega. The resulting flux ratio between the stellar photosphere and the debris disk amounts to 1.29 +/- 0.19% within the FLUOR field-of-view (similar to 7.8 AU). Finally, we complement our K-band study with archival photometric and interferometric data in order to evaluate the main physical properties of the inner dust disk. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations.