Observational Possibility of the "Snow Line" on the Surface of Circumstellar Disks with the Scattered Light

TL;DR

This paper proposes a new observational method to spatially resolve the snow line on circumstellar disks by detecting the 3 micron water ice feature in scattered light, aiding understanding of planet formation and disk structure.

Contribution

It introduces a novel approach using 3 micron water ice feature in scattered light to locate the snow line on circumstellar disks with current instruments.

Findings

The 3 micron water ice feature is detectable in scattered light from disks.

The method allows spatial resolution of the snow line.

Disk dust properties can be diagnosed using color diagrams.

Abstract

We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on the planet formation, on the isotopic anomaly in meteorites, and on the origin of the sea on the Earth. Therefore, the spatially resolved observation of the condensation/sublimation front of ice, so-called ``snow line'' is strongly required. Here, we propose a new method for obtaining the spatially resolved ``snow line'' on the circumstellar disks by observing 3 \micron H$_2$O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H$_2$O ice feature from protoplanetary disks are detectable and spatially resolvable with the current instruments through a $H_2O$ narrowband filter around 3 \micron. Finally, we present a diagnostics of disk dust properties on the $K-H_2O$ and $K-L'$ two color diagram.