Multi-Epoch Detections of Water Ice Absorption in Edge-on Disks around Herbig Ae Stars: PDS 144N and PDS 453

TL;DR

This study detects water ice absorption in the disks of two Herbig Ae stars over multiple epochs, revealing lower ice abundance than in low-mass stars likely due to UV radiation effects, and suggests possible temporal variability.

Contribution

First multi-epoch detection of water ice in Herbig Ae star disks, showing UV radiation impacts and potential temporal changes in ice absorption features.

Findings

Water ice absorption detected in PDS 144N and PDS 453 disks.

Optical depths are lower than in similar low-mass star systems.

Possible variability of water ice feature over multiple observations.

Abstract

We report the multi-epoch detections of the water ice in 2.8-4.2 micron spectra of two Herbig Ae stars, PDS 144N (A2 IVe) and PDS 453 (F2 Ve), which have an edge-on circumstellar disk. The detected water ice absorption is found to originate from their protoplanetary disks. The spectra show a relatively shallow absorption of water ice around 3.1 micron for both objects. The optical depths of the water ice absorption are ~0.1 and ~0.2 for PDS 144N and PDS 453, respectively. Compared to the water ice previously detected in low-mass young stellar objects with an edge-on disk with a similar inclination angle, these optical depths are significantly lower. It suggests that stronger UV radiation from the central stars effectively decreases the water ice abundance around the Herbig Ae stars through photodesorption. The water ice absorption in PDS 453 shows a possible variation of the feature among the six observing epochs. This variation could be due to a change of absorption materials passing through our line-of-sight to the central star.