SIMBAD references

In the framework of the Water In Star-forming regions with Herschel (WISH) key program, several H₂O (E_u>190K), high-J CO, [OI], and OH transitions are mapped with Herschel-PACS in two shock positions along two prototypical outflows around the low-luminosity sources L1448 and L1157. Previous Herschel-HIFI H₂O observations (E_u=53-249K) are also used. The aim is to derive a complete picture of the excitation conditions at the selected shock positions. We adopted a large velocity gradient analysis (LVG) to derive the physical parameters of the H₂O and CO emitting gas. Complementary Spitzer mid-IR H₂ data were used to derive the H₂O abundance. Consistent with other studies, at all selected shock spots a close spatial association between H₂O, mid-IR H₂, and high-J CO emission is found, whereas the low-J CO emission traces either entrained ambient gas or a remnant of an older shock. The excitation analysis, conducted in detail at the L1448-B2 position, suggests that a two-component model is needed to reproduce the H₂O, CO, and mid-IR H₂ lines: an extended warm component (T∼450K) is traced by the H₂O emission with E_u=53-137K and by the CO lines up to J=22-21, and a compact hot component (T=1100K) is traced by the H₂O emission with E_u>190K and by the higher-J CO transitions. At L1448-B2 we obtain an H₂O abundance (3-4)x10^–6 for the warm component and (0.3-1.3)x10^–5 for the hot component and a CO abundance of a few 10^–5 in both components. In L1448-B2 we also detect OH and blue-shifted [OI] emission, spatially coincident with the other molecular lines and with [FeII] emission. This suggests a dissociative shock for these species, related to the embedded atomic jet. On the other hand, a non-dissociative shock at the point of impact of the jet on the cloud is responsible for the H₂O and CO emission. The other examined shock positions show an H₂O excitation similar to L1448-B2, but a slightly higher H₂O abundance (a factor of ∼4). The two gas components may represent a gas stratification in the post-shock region. The extended and low-abundance warm component traces the post-shocked gas that has already cooled down to a few hundred Kelvin, whereas the compact and possibly higher-abundance hot component is associated with the gas that is currently undergoing a shock episode. This hot gas component is more affected by evolutionary effects on the timescales of the outflow propagation, which explains the observed H₂O abundance variations.