Dust in the inner regions of debris disks around A stars

TL;DR

This study uses infrared interferometry to detect and model hot dust close to A-type stars beta Leo and zeta Lep, revealing spatially distinct dust populations and providing insights into debris disk evolution.

Contribution

First direct interferometric detection of near-infrared excess dust in the inner regions of debris disks around A stars, with simple geometric models explaining their spatial distribution.

Findings

Near-infrared excess dust is within a few AU of the stars.

Dust near the sublimation radius is likely responsible for the excess.

Spatially distinct dust populations are present in the disks.

Abstract

We present infrared interferometric observations of the inner regions of two A-star debris disks, beta Leo and zeta Lep, using the FLUOR instrument at the CHARA interferometer on both short (30 m) and long (>200 m) baselines. For the target stars, the short baseline visibilities are lower than expected for the stellar photosphere alone, while those of a check star, delta Leo, are not. We interpret this visibility offset of a few percent as a near-infrared excess arising from dust grains which, due to the instrumental field of view, must be located within several AU of the central star. For beta Leo, the near-infrared excess producing grains are spatially distinct from the dust which produces the previously known mid-infrared excess. For zeta Lep, the near-infrared excess may be spatially associated with the mid-infrared excess producing material. We present simple geometric models which are consistent with the near and mid-infrared excess and show that for both objects, the near-infrared producing material is most consistent with a thin ring of dust near the sublimation radius with typical grain sizes smaller than the nominal radiation pressure blowout radius. Finally, we discuss possible origins of the near-infrared emitting dust in the context of debris disk evolution models.