Abstract
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.
Highlights
The discovery of a debris disc around Vega (HD 172167, A0V, 7.76 pc) by Aumann et al (1984) was one of the first hints that extrasolar planetary systems exist
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
The analysis presented in the previous section confirms that the most straightforward scenario for explaining the visibility deficit is the presence of hot dust grains producing thermal emission in the near-infrared
Summary
The discovery of a debris disc around Vega (HD 172167, A0V, 7.76 pc) by Aumann et al (1984) was one of the first hints that extrasolar planetary systems exist. Infrared observations revealed a smooth axi-symmetric structure extending from 85 to at least to 815 AU and containing about 3 × 10−3 M⊕ of dust grains (e.g., Su et al 2005; Rieke et al 2005; Sibthorpe et al 2010) This huge size of the disc seen in the infrared came as a surprise and raised several questions about the mechanism at the origin of the dust. Profile using intermediate size grains in elliptical orbits around the parent planetesimal ring, and conclude that it is consistent with a steady-state model Another interesting model that was able to reproduce the infrared observations suggests that the debris disc of Vega is the result of icy planet formation (Kenyon & Bromley 2008). On a longer time scale, the characterisation of inner debris discs is relevant for preparing the programme of future space missions dedicated to the direct detection and characterisation of Earth-like planets, since the presence of large quantities of warm dust in the habitable zone around nearby main sequence stars might jeopardize the success of such missions (Roberge et al 2009; Defrère et al 2010)
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