Herschel/HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2

Herschel/HIFI observations of water from the intermediate mass protostar NGC 7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four H_2^(16)O and two H_2^(18)O lines, were observed and all but one H_2^(18)O line were detected. The four H_2 ^(16)O lines discussed here share a similar morphology: a narrower, ≈6km s^(−1), component centered slightly redward of the systemic velocity of NGC7129 FIRS 2 and a much broader, ≈25 km s^(−1) component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H_2O is constrained to ≈10^(−7) for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H_2O/CO relative abundance is found to be ≈0.2, appears to be tracing the same energetic region that produces strong CO emission at high J

Herschel/HIFI detections of hydrides towards AFGL 2591: Envelope emission versus tenuous cloud absorption

The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH^+, NH, OH^+, H_2O^+, while NH^+ and SH^+ have not been detected. All molecules except for CH and CH^+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(J_(F,P) = 3/2_(2,−) − 1/2_(1,+)) and CH^+(J = 1−0, J = 2−1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH^+ emission stems from the envelope. The observed abundance and excitation of CH and CH^+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules

Water cooling of shocks in protostellar outflows: Herschel-PACS map of L1157

Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H_2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H_2O 179 μm transition obtained toward the young outflow L1157. Methods. The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H_2O abundance and total cooling. Results. Strong H_2O peaks are localized on both shocked emission knots and the central source position. The H_2O 179 μm emission is spatially correlated with emission from H_2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH_3. A strong H_2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H_2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H_2O  abundance of the order of 10^(-4). This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H_2O cooling is ~10^(-1) L_☉, about 40% of the cooling due to H_2 and 23% of the total energy released in shocks along the L1157 outflow