This is a repository copy of Candidate Water Vapor Lines to Locate the H O Snowline 2 Through High-dispersion Spectroscopic Observations . II . The Case of a Herbig Ae Star

Observationally measuring the location of the H2O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. In disks around Herbig Ae stars (T∗ ∼10,000K,M∗ &2.5M⊙), the position of the H2O snowline is further from the central star compared with that around cooler, and less massive T Tauri stars. Thus, the H2O emission line fluxes from the region within the H2O snowline are expected to be stronger. In this paper, we calculate the chemical composition of a Herbig Ae disk using chemical kinetics. Next, we calculate the H2O emission line profiles, and investigate the properties of candidate water lines across a wide range of wavelengths (from mid-infrared to sub-millimeter) that can locate the position of the H2O snowline. Those line identified have small Einstein A coefficients (∼ 10− 10 s) and relatively high upper state energies (∼ 1000K). The total fluxes tend to increase with decreasing wavelengths. We investigate the possibility of future observations (e.g., ALMA, SPICA/SMI-HRS) to locate the position of the H2O snowline. Since the fluxes of those identified lines from Herbig Ae disks are stronger than those from T Tauri disks, the possibility of a successful detection is expected to increase for a Herbig Ae disk. Subject headings: astrochemistry— protoplanetary disks— ISM: molecules— sub-millimeter & infrared: planetary systems— stars: formation