Paper detail

Hot exozodiacal dust resolved around Vega with IOTA/IONIC

Although debris discs have been detected around a significant number of main-sequence stars, only a few of them are known to harbour hot dust in their inner part where terrestrial planets may have formed. Thanks to infrared interferometric observations, it is possible to obtain a direct measurement of these regions, which are of prime importance for preparing future exo-Earth characterisation missions. In this context, we have resolved the exozodiacal dust disc around Vega with the help of infrared stellar interferometry and estimated the integrated H-band flux originating from the first few AUs of the debris disc. Using precise H-band interferometric measurements obtained with the 3-telescope IOTA/IONIC interferometer (Mount Hopkins, Arizona), thorough modelling of both interferometric data (squared visibility and closure phase) and spectral energy distribution was performed to constrain the nature of the near-infrared excess emission. The most straightforward scenario consists in a compact dust disc producing a thermal emission that is largely dominated by small grains located between 0.1 and 0.3 AU from Vega and accounting for 1.23 +/- 0.45% of the near-infrared stellar flux for our best-fit model. This flux ratio is shown to vary slightly with the geometry of the model used to fit our interferometric data (variations within +/-0.19%). Initially revealed by K-band CHARA/FLUOR observations, the presence of hot exozodiacal dust in the vicinity of Vega is confirmed by our H-band IOTA/IONIC measurements at the 3-sigma level. Whereas the origin of the dust is still uncertain, its presence and the possible connection with the outer disc suggest that the Vega system is currently undergoing major dynamical perturbations.