Probing the Early Stages of Low‐Mass Star Formation in LDN 1689N: Dust and Water in IRAS 16293−2422A, B, and E

We present deep images of dust continuum emission at 450, 800, and 850 micronof the dark cloud LDN 1689N which harbors the low-mass young stellar objects(YSOs) IRAS 16293-2422A and B (I16293A and I16293B) and the cold prestellarobject I16293E. Toward the positions of I16293A and E we also obtained spectraof CO-isotopomers and deep submillimeter observations of chemically relatedmolecules with high critical densities. To I16293A we report the detection ofthe HDO 1_01 - 0_00 and H2O 1_10 - 1_01 ground-state transitions as broadself-reversed emission profiles with narrow absorption, and a tentativedetection of H2D+ 1_10 - 1_11. To I16293E we detect weak emission ofsubthermally excited HDO 1_01 - 0_00. Based on this set of submillimetercontinuum and line data we model the envelopes around I16293A and E. Thedensity and velocity structure of I16293A is fit by an inside-out collapsemodel, yielding a sound speed of a=0.7 km/s, an age of t=(0.6--2.5)e4 yr, and amass of 6.1 Msun. The density in the envelope of I16293E is fit by a radialpower law with index -1.0+/-0.2, a mass of 4.4 Msun, and a constant temperatureof 16K. These respective models are used to study the chemistry of theenvelopes of these pre- and protostellar objects. The [HDO]/[H2O] abundance ratio in the warm inner envelope of I16293A of afew times 1e-4 is comparable to that measured in comets. This supports the ideathat the [HDO]/[H2O] ratio is determined in the cold prestellar core phase andconserved throughout the formation process of low-mass stars and planets.Comment: 61 pages, 17 figures. Accepted for publication in ApJ. To get Fig. 13: send email to stark@strw.leidenuniv.n