Deuterium Enhancement in Water toward Orion IRc2 Deduced from HDO Lines above 800 GHz

Abstract

We present the —rst detection of two submillimeter lines of HDO in the KL region of Orion: J Ka,Kb (848.9619 GHz), and (893.6387 GHz). The —rst line has been mapped at 10A 2 1,2 ] 1 1,1 1 1,1 ] 0 0,0 angular resolution. These transitions involve some of the lowest energy levels of HDO and have the shortest wavelengths accessible from the ground. Therefore, they provide a perfect tool to complement previous works that made use of millimeter HDO transitions involving similar energy levels (1 1,0 ] 1 1,1 at 80.6 GHz, at 241.6 GHz, and others). The two submillimeter lines arise from the moderate 2 1,1 ] 2 1,2 expanding material or ii Plateau ˇˇ km s~1, *v ” 20 km s~1). The emission is very compact in (v LSR D 9 both HDO transitions (no more extended than D40A¨45A) with similar intensities, line shapes, and line widths. The Hot Core seems completely hidden in our data in contrast with the majority of other millimeter-wave observations. This fact can only be explained if the Hot Core is embedded or behind the region of the out—ow. The high line opacity of the submillimeter HDO lines would then hide the Hot Core emission. A comparison with our previously published high angular resolution data para-H 2 O