Abstract
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. 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. We performed precise visibility measurements at both short (~30 m) and long (~150 m) baselines with the FLUOR beam-combiner 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). After revising Vega's K-band angular diameter (3.202+/-0.005 mas), we show that a significant deficit in squared visibility (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 (~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.
Highlights
Vega (HD 172167, A0V, 7.76 pc) is probably one of the most important stars in astrophysics, as it has been used as a photometric standard for more than a century (Hearnshaw 1996)
We have presented high precision visibility measurements obtained on Vega at the CHARA Array with the FLUOR beam-combiner
The presence of a significant deficit of visibility at short baselines with respect to a simple uniform disk stellar model led us to the conclusion that an additional source of K-band emission is present in the FLUOR field-of-view centred around Vega (1 in radius), with an estimated excess of 1.29 ± 0.19% relative to the photospheric emission
Summary
Vega (HD 172167, A0V, 7.76 pc) is probably one of the most important stars in astrophysics, as it has been used as a photometric standard for more than a century (Hearnshaw 1996). With the advent of infrared space-based telescopes, it was discovered to have a large infrared excess beyond 12 μm with respect to its expected photospheric flux (Aumann et al 1984) This was identified as the thermal emission from a circumstellar disk of cool dust located at about 85 AU from Vega. Due to the limitation in angular resolution of current telescopes, very little is known about the innermost part of these debris disks, which could potentially harbour warm dust (>∼300 K) heated by the star as suggested by Fajardo-Acosta et al (1998) Such warm dust would have a signature in the near- and mid-infrared that only photometric studies have attempted to detect until recently. In order to better constrain the near-infrared brightness of Vega’s disk, we have used the same method at the CHARA Array (ten Brummelaar et al 2005) with an optimised set of baselines
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