Hot exozodiacal dust resolved around Vega with IOTA/IONIC

¹ Max Planck Institut für Radioastronomie, Auf den Hügel 69, 53121 Bonn, Germany
e-mail: ddefrere@mpifr-bonn.mpg.de
² Dept. d’Astrophysique, Géophysique & Océanographie, Université de Liège, 17 Allée du Six Août, 4000 Liège, Belgium
³ UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
⁴ Laboratoire AIM, CEA Saclay-Université Paris Diderot-CNRS, DSM/Irfu/Service d’Astrophysique, 91191 Gif-sur-Yvette, France
⁵ European Southern Observatory, Alonso de Cordova, 3107 Vitacura, Chile
⁶ LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁷ NASA Exoplanet Science Institute (Caltech), MS 100-22, 770 South Wilson Avenue, Pasadena, CA 91125, USA
⁸ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
⁹ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ Jet Propulsion Laboratory (NASA/JPL), MS 301-355, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Received: 4 April 2011
Accepted: 2 August 2011

Abstract

Context. 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.

Aims. We resolve the exozodiacal dust disc around Vega with the help of infrared stellar interferometry and estimate the integrated H-band flux originating from the first few AUs of the debris disc.

Methods. Precise H-band interferometric measurements were obtained on Vega 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.

Results. Resolved circumstellar emission within  ~6 AU from Vega is identified at the 3-σ level. 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%).

Conclusions. The presence of hot exozodiacal dust in the vicinity of Vega, initially revealed by K-band CHARA/FLUOR observations, is confirmed by our H-band IOTA/IONIC measurements. 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.