The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants

TL;DR

This study used the Keck Aperture Masking Experiment to spatially resolve dust formation regions around 20 dust-enshrouded AGB stars, revealing asymmetric dust shells and measuring sublimation temperatures, advancing understanding of dust-driven winds in evolved stars.

Contribution

First high-resolution near-infrared imaging of multiple dust-enshrouded AGB stars, providing new insights into dust shell asymmetries and sublimation temperatures across different dust types.

Findings

45% of targets show measurable elongations indicating asymmetric dust shells.

Sublimation temperatures are around 1130 K for silicates and 1170 K for amorphous carbon.

Inner dust shell temperature profiles change with optical thickness, possibly due to dust clumping at high mass-loss rates.

Abstract

While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 microns and 3.1 microns. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC+10216 or CIT6. Using radiative transfer models, we find the sublimation temperature of 1130 +- 90 K and 1170 +- 60 K for silicates and amorphous carbon respectively, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells (tau > 2 at 2.2 microns), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.