Dust Continuum Emission and the Upper Limit Fluxes of Submillimeter Water Lines of the Protoplanetary Disk around HD 163296 Observed by ALMA

Notsu, Shota; Akiyama, Eiji; Booth, Alice; Nomura, Hideko; Walsh, Catherine; Hirota, Tomoya; Honda, Mitsuhiko; Tsukagoshi, Takashi; Millar, T. J.

In this paper, we analyze the upper limit fluxes of submillimeter ortho-H2 16O 321 GHz, para-H2 18O 322 GHz, and HDO 335 GHz lines from the protoplanetary disk around the Herbig Ae star HD 163296, using the Atacama Large Millimeter/Submillimeter Array. These water lines are considered to be the best candidate submillimeter lines to locate the position of the H2O snowline, on the basis of our previous model calculations. We compare the upper limit fluxes with the values calculated by our models with dust emission included, and we constrain the line-emitting region and the dust opacity from the observations. We conclude that, if the outer edge of the region with a high water abundance and the position of the water snowline are both beyond 8 au, then themillimeter dust opacity κ mm will have a value larger than 2.0 cm2 g−1. In addition, the position of the water snowline must lie inside 20 au if the millimeter dust opacity κ mm is 2.0 cm2 g−1. Future observations of the dust continuum emission at higher angular resolution and submillimeter water lines with a longer observation time are required to clarify the detailed structures and the position of the H2O snowline in the disk midplane.

DOI: 10.3847/1538-4357/ab0ae9