The Foggy Disks Surrounding Herbig Ae Stars: a Theoretical Study of the H2O Line Spectra

TL;DR

This paper provides a theoretical analysis of water line spectra in proto-planetary disks around Herbig Ae stars, predicting observability with Herschel and ground telescopes, and discusses the diagnostic potential and uncertainties involved.

Contribution

It offers the first detailed theoretical predictions of water line spectra in Herbig Ae star disks, considering various physical and chemical model parameters.

Findings

Several water lines are predicted to be observable with Herschel's HIFI instrument.

Some maser lines could be detectable with ground-based telescopes.

Water line observations can serve as powerful diagnostics, but are sensitive to model assumptions.

Abstract

Water is a key species in many astrophysical environments, but it is particularly important in proto-planetary disks. So far,observations of water in these objects have been scarce, but the situation should soon change thanks to the Herschel satellite. We report here a theoretical study of the water line spectrum of a proto-planetary disk surrounding Ae stars. We show that several lines will be observable with the HIFI instrument onboard the Herschel Space Observatory. We predict that some maser lines could also be observable with ground telescopes and we discuss how the predictions depend not only on the adopted physical and chemical model but also on the set of collisional coefficients used and on the H2 ortho to para ratio through its effect on collisional excitation. This makes the water lines observations a powerful, but dangerous -if misused- diagnostic tool.