Water ice at the surface of HD 100546 disk

TL;DR

This study detects water ice on the surface of the HD 100546 disk using near-infrared imaging, suggesting UV photodesorption influences ice grain survival, but further precise measurements are needed for definitive conclusions.

Contribution

First direct detection of water ice absorption feature on a Herbig Be star disk surface using multicolor near-infrared imaging.

Findings

Water ice absorption feature detected at 3.1 μm.

Observed absorption depth slightly favors models including photodesorption effects.

UV photons likely influence ice grain survival on the disk surface.

Abstract

We made near infrared multicolor imaging observations of a disk around Herbig Be star HD100546 using Gemini/NICI. K (2.2\,$\mu$m), H$_2$O ice (3.06\,$\mu$m), and L'(3.8\,$\mu$m) disk images were obtained and we found the 3.1\,$\mu$m absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on \cite{Oka2012} including water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by the both disk models with/without photodesorption effect within the measurement accuracy, but slightly favors the model with photodesorption effects, implying that the UV photons play an important role on the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement on the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models.