Candidate Water Vapor Lines to Locate the H2O Snowline 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 planetesimal and planet formation processes, and the origin of water on Earth. In disks around Herbig Ae stars (T-* similar to 10,000 K, M-* greater than or similar to 2.5M circle dot), the position of the H2O snowline is farther 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 submillimeter) that can locate the position of the H2O snowline. Those lines identified have small Einstein A coefficients (similar to 10(-6)-10(-3) s(-1)) and relatively high upperstate energies (similar to 1000 K). The total fluxes tend to increase with decreasing wavelengths. We investigate the possibility of future observations (e.g., ALMA, SPICA/SMI-HRS) locating 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.