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.

Abstract. We present submillimeter observations of rotational transitions of carbon monoxide from J = 2 → 1 up to 7 → 6 for a sample of Asymptotic Giant Branch stars and red supergiants. It is the first time that the high transitions J = 6 → 5 and 7 → 6 are included in such a study. With line radiative transfer calculations, we aim to determine the mass-loss history of these stars by fitting the CO line intensities. We find that the observed line intensities of the high transitions, including the J = 4 → 3 transition, are significantly lower than the predicted values. We conclude that the physical structure of the outflow of Asymptotic Giant Branch stars is more complex than previously thought. In order to understand the observed line intensities and profiles, a physical structure with a variable mass-loss rate and/or a gradient in stochastic gas velocity is required. A case study of the AGB star WX Psc is performed. We find that the CO line strengths may be explained by variations in mass-loss on time scales similar to those observed in the separated arc-like structures observed around post-AGB stars. In addition, a gradient in the stochastic velocity may play a role. Until this has been sorted out fully, any mass loss determinations based upon single CO lines will remain suspect.

We report the detection of the 1 10 -1 11 ground-state transition of ortho-H 2 D ϩ at 372.421 GHz in emission from the young stellar object NGC 1333 IRAS 4A. Detailed excitation models with a power-law temperature and density structure yield a beam-averaged H 2 D ϩ abundance of with an uncertainty of a factor of 2. The Ϫ12 3 # 10 line was not detected toward W33A, GL 2591, and NGC 2264 IRS (in the latter source at a level that is 3-8 times lower than previous observations). The

Abstract. We present models and observations of gas-phase H 2 O lines between 5 and 540 µm toward deeply embedded massive protostars, involving both pure rotational and ro-vibrational transitions. The data have been obtained for 6 sources with both the Short and Long Wavelength Spectrometers (SWS and LWS) on board the Infrared Space Observatory (ISO) and with the Submillimeter Wave Astronomy Satellite (SWAS). For comparison, CO J = 7−6 spectra have been observed with the MPIfR/SRON 800 GHz heterodyne spectrometer at the James Clerk Maxwell Telescope (JCMT). A radiative transfer model in combination with different physical/chemical scenarios has been used to model these H 2 O lines for 4 sources to probe the chemical structure of these massive protostars. The results indicate that pure gas-phase production of H 2 O cannot explain the observed spectra. Ice evaporation in the warm inner envelope and freeze-out in the cold outer part are important for most of our sources and occur at T ∼ 90-110 K. The ISO-SWS data are particularly sensitive to ice evaporation in the inner part whereas the ISO-LWS data are good diagnostics of freeze-out in the outer region. The modeling suggests that the 557 GHz SWAS line includes contributions from both the cold and the warm H 2 O gas. The SWAS line profiles indicate that for some of the sources a fraction of up to 50% of the total flux may originate in the outflow. Shocks do not seem to contribute significantly to the observed emission in other H 2 O lines, however, in contrast with the case for Orion. The results show that three of the observed and modeled H 2 O lines, the 3 03 −2 12 , 2 12 −1 01 , and 1 10 −1 01 lines, are good candidates to observe with the Herschel Space Observatory in order to further investigate the physical and chemical conditions in massive star-forming regions.