An interferometric study of the Fomalhaut inner debris disk. I. Near-infrared detection of hot dust with VLTI/VINCI

TL;DR

This study uses near-infrared interferometry to detect hot dust close to Fomalhaut, revealing circumstellar emission likely from hot dust within 6 AU, and refines the star's diameter measurement.

Contribution

First interferometric detection of hot dust around Fomalhaut, providing insights into its inner debris disk structure and updated stellar diameter.

Findings

Detected circumstellar emission at 0.88% flux relative to star

Ruled out off-axis point sources as emission origin

Revised Fomalhaut's limb-darkened diameter to 2.223 mas

Abstract

The innermost parts of dusty debris disks around main sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared interferometry, we aim to detect the signature of hot dust around the nearby A4 V star Fomalhaut, which has already been suggested to harbor a warm dust population in addition to a cold dust ring located at about 140 AU. Archival data obtained with the VINCI instrument at the VLTI are used to study the fringe visibility of the Fomalhaut system at projected baseline lengths ranging from 4 m to 140 m in the K band. A significant visibility deficit is observed at short baselines with respect to the expected visibility of the sole stellar photosphere. This is interpreted as the signature of resolved circumstellar emission, producing a relative flux of 0.88% +/- 0.12% with respect to the stellar photosphere. While our interferometric data cannot directly constrain the morphology of the excess emission source, complementary data from the literature allow us to discard an off-axis point-like object as the source of circumstellar emission. We argue that the thermal emission from hot dusty grains located within 6 AU from Fomalhaut is the most plausible explanation for the detected excess. Our study also provides a revised limb-darkened diameter for Fomalhaut (2.223 +/- 0.022 mas), taking into account the effect of the resolved circumstellar emission.