Hot exozodiacal dust resolved around Vega with IOTA/IONIC

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.

Interferometric observations of rapidly rotating stars

“…Further scientifically significant data from interferometer on this object came with the longer baselines of PTI when Ciardi et al (2001) observed it and found puzzling signs of residuals in the K-band fits, consistent with a debris disk signal contaminating the stellar photospheric signal (as discussed in more detail in Barnes 2009;Lawler et al 2009;Akeson et al 2009). This finding was consistent with the further investigations with the CHARA Array and IOTA (Defrère et al 2011). These PTI and CHARA Array interferometric studies set the stage for two further, more detailed, studies of the star's photosphere itself.…”

Near-infrared emission from sublimating dust in collisionally active debris disks

“…This means that not only the cross-section, but also the mass is dominated by barely bound grains in the innermost parts of the disk. Interestingly, such steep size distributions are also invoked to explain NIR interferometric observations of hot exozodiacal dust (Defrère et al 2011;Mennesson et al 2013;Lebreton et al 2013). The drop in the size distribution from β ≈ 0.5 to β ≈ 1 is also much more pronounced in the inner disk than in the parent belt.…”

“…There are two additional problems with this scenario, which also serve as clues for solving the hot exozodiacal dust mystery. (1) Hot exozodiacal dust is thought to consist mostly of blowout grains with sizes around 0.01-0.1 µm (Akeson et al 2009;Defrère et al 2011;Mennesson et al 2013;Lebreton et al 2013), while P-R drag only transports bound grains to the sublimation zone, the smallest of which have sizes of about 1 µm. (2) The dust distribution resulting from the balance between P-R drag and collisions yields an SED with a positive slope in the infrared domain, while observations find negative slopes (e.g., Akeson et al 2009;Acke et al 2012), and the pile-up of dust is too inefficient to have an effect on the slope of the SED 15 .…”

“…The dust can be studied by observing its infrared and (sub-)millimeter emission, as well as the stellar radiation it scatters, and is usually found at large distances from the star (tens of AUs, Carpenter et al 2009). Recently, interferometric observations have found excess nearinfrared (NIR) emission emanating from the innermost parts of several debris disks, which has been interpreted as thermal emission from hot (>1000 K) dust (Ciardi et al 2001;Absil et al 2006Absil et al , 2008Absil et al , 2009di Folco et al 2007;Akeson et al 2009;Defrère et al 2011Defrère et al , 2012 Table 1 for an overview). This material is known as hot exozodiacal dust.…”

“…(e) For η Lep, 110 Her, 10 Tau, ξ Boo, and κ CrB, the possibility that the observed NIR excess is due to a low-mass companion within the field-of-view cannot be excluded . Morphological models of exozodiacal dust disks, constrained by the NIR observations, indicate that the hot dust is concentrated in a sharply peaked ring, whose inner boundary is determined by dust sublimation (Defrère et al 2011;Mennesson et al 2013;Lebreton et al 2013). The process of dust sublimation may therefore play an important role in shaping exozodiacal clouds.…”