We present deep images of dust continuum emission at 450, 800, and 850 m of the dark cloud LDN 1689N, which harbors the low-mass young stellar objects (YSOs) IRAS 16293À2422 A and B (I16293A and I16293B) and the cold prestellar object I16293E. Toward the positions of I16293A and I16293E we also obtained spectra of CO-isotopomers and deep submillimeter observations of chemically related molecules with high critical densities (HCO + , H 13 CO + , DCO + , H 2 O, HDO, and H 2 D + ). Toward I16293A we report the detection of the HDO 1 01 -0 00 and H 2 O 1 10 -1 01 ground-state transitions as broad self-reversed emission profiles with narrow absorption and a tentative detection of H 2 D + 1 10 -1 11 . Toward I16293E we detect weak emission of subthermally excited HDO 1 01 -0 00 . Based on this set of submillimeter continuum and line data, we model the envelopes around I16293A and I16293E. The density and velocity structure of I16293A is fitted by an inside-out collapse model, yielding a sound speed of a ¼ 0:7 km s À1 , an age of t ¼ (0:6 2:5) Â 10 4 yr, and a mass of 6.1 M . The density in the envelope of I16293E is fitted by a radial power law with index À1:0 AE 0:2, a mass of 4.4 M , and a constant temperature of 16 K. These respective models are used to study the chemistry of the envelopes of these pre-and protostellar objects. We made a large, fully sampled CO J ¼ 2 1 map of LDN 1689N, which clearly shows the two outflows from I16293A and I16293B and the interaction of one of the flows with I16293E. An outflow from I16293E reported elsewhere is not confirmed. Instead, we find that the motions around I16293E identified from small maps are part of a larger scale fossil flow from I16293B. Modeling of the I16293A outflow shows that the broad HDO, water ground state, and CO J ¼ 6 5 and 7-6 emission lines originate in this flow, while the HDO and H 2 O line cores originate in the envelope. The narrow absorption feature in the ground-state water lines is due to cold gas in the outer envelope. The derived H 2 O abundance is 3 Â 10 À9 in the cold regions of the envelope of I16293A (T kin < 14 K), 2 Â 10 À7 in warmer regions of the envelope (>14 K), and 10 À8 in the outflow. The HDO abundance is constant at a few times 10 À10 throughout the envelopes of I16293A and I16293E. Because the derived H 2 O and HDO abundances in the two objects can be understood through shock chemistry in the outflow and ion-molecule chemistry in the envelopes, we argue that both objects are related in chemical evolution. The [HDO]/[H 2 O] abundance ratio in the warm inner envelope of I16293A of a few times 10 À4 is comparable to that measured in comets. This supports the idea that the [HDO]/[H 2 O] ratio is determined in the cold prestellar core phase and conserved throughout the formation process of low-mass stars and planets.

We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the 1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL 2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and B335. We also present a small map of the water emission in S140. Observations of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission was detected. The abundance of ortho-water relative to H_2 in the giant molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five of the cloud cores in our sample have previous water detections; however, in all cases the emission is thought to arise from hot cores with small angular extents. The water abundance estimated for the hot core gas is at least 100 times larger than in the gas probed by SWAS. The most stringent upper limit on the ortho-water abundance in dark clouds is provided in TMC-1, where the 3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.Comment: 5 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty (included), and apjfonts.sty (included

No abstract

No abstract

We have observed the 1 10 -1 01 pure rotational transitions of both H 2 16 O and H 2 18 O toward Sagittarius B2 using the Submillimeter Wave Astronomy Satellite. The spectra thereby obtained show a complex pattern of absorption and-in the case of H 2 16 O-emission, with numerous features covering a wide range of LSR velocities (Ϫ130 to 130 km s Ϫ1 ) and representing absorption both in gas associated with Sgr B2 as well as by several components of foreground gas along the line of sight. The ortho-water abundance derived for the absorbing foreground gas is ∼ relative to H 2 . Ϫ76 # 10