2019ApJ...875...96N

In this paper, we analyze the upper limit fluxes of submillimeter ortho-H₂¹⁶O 321 GHz, para-H₂¹⁸O 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.