Herschel observations of the Herbig-Haro objects HH52-54
Journal article, 2011

Context. The emission from Herbig-Haro objects and supersonic molecular outflows is understood as cooling radiation behind shocks, which are initiated by a (proto-)stellar wind or jet. Within a given object, one often observes both dissociative (J-type) and non-dissociative (C-type) shocks, owing to the collective effects of internally varying shock velocities. Aims. We aim at the observational estimation of the relative contribution to the cooling by CO and H(2)O, as this provides decisive information for understanding the oxygen chemistry behind interstellar shock waves. Methods. The high sensitivity of HIFI, in combination with its high spectral resolution capability, allowed us to trace the H(2)O outflow wings at an unprecedented signal-to-noise ratio. From the observation of spectrally resolved H(2)O and CO lines in the HH52-54 system, both from space and from the ground, we arrived 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 accelerated lambda iteration code, where we use the fact that variable shock strengths, distributed along the front, are naturally implied by a curved surface. Results. Based on observations of CO and H(2)O 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-H(2)O-cooling-rate >> 1. Formally, we derived the ratio A(CO)/A(o-H(2)O) = 10, which is in good agreement with earlier determination of 7 based on ISO-LWS observations. From the best-fit model to the CO emission, we arrive at an H(2)O abundance close to 1 x 10(-5). The line profiles exhibit two components, one that is triangular and another that is a superposed, additional feature. This additional feature is likely to find its origin in a region that is smaller than the beam where the ortho-water abundance is smaller than in the quiescent gas. Conclusions. Comparison with recent shock models indicate that a planar shock cannot 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 are derived than predicted by these types of shocks.

stars: formation

Herbig-Haro objects

and outflows

line emission

outflows

odin

radiative-transfer

spitzer c2d

ISM: molecules

molecular-hydrogen emission

water

interstellar shock-waves

survey

magnetic-fields

ISM: jets

protostellar outflows

stars: winds

dark-cloud

Author

Per Bjerkeli

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

René Liseau

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

B. Nisini

Osservatorio Astronomico di Roma

M. Tafalla

M. Benedettini

Arcetri Astrophysical Observatory

Per Bergman

Chalmers, Earth and Space Sciences, Onsala Space Observatory

O. Dionatos

Kobenhavns Universitet

T. Giannini

Osservatorio Astronomico di Roma

G. J. Herczeg

Max Planck Institute

Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

B. Larsson

Stockholm University

C. McCoey

University of Waterloo

Michael Olberg

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Henrik Olofsson

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 533 A80

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

DOI

10.1051/0004-6361/201116846