Herschel observations of the Herbig-Haro objects HH52-54
  We are aiming at the observational estimation of the relative contribution to
the cooling by CO and H2O, as this provides decisive information for the
understanding of the oxygen chemistry behind interstellar shock waves. Methods.
The high sensitivity of HIFI, in combination with its high spectral resolution
capability, allows us to trace the H2O outflow wings at unprecedented
signal-to-noise. From the observation of spectrally resolved H2O and CO lines
in the HH52-54 system, both from space and from ground, we arrive at the
spatial and velocity distribution of the molecular outflow gas. Solving the
statistical equilibrium and non-LTE radiative transfer equations provides us
with estimates of the physical parameters of this gas, including the cooling
rate ratios of the species. The radiative transfer is based on an ALI code,
where we use the fact that variable shock strengths, distributed along the
front, are naturally implied by a curved surface. Based on observations of CO
and H2O spectral lines, we conclude that the emission is confined to the HH54
region. The quantitative analysis of our observations favours a ratio of the
CO-to-H2O-cooling-rate >> 1. From the best-fit model to the CO emission, we
arrive at an H2O abundance close to 1e-5. The line profiles exhibit two
components, one of which is triangular and another, which is a superposed,
additional feature. This additional feature likely originates from a region
smaller than the beam where the ortho-water abundance is smaller than in the
quiescent gas. Comparison with recent shock models indicate that a planar shock
can not easily explain the observed line strengths and triangular line
profiles.We conclude that the geometry can play an important role. Although
abundances support a scenario where J-type shocks are present, higher cooling
rate ratios than predicted by these type of shocks are derived.
