First spectrally-resolved H-2 observations towards HH 54 Low H2O abundance in shocks
Journal article, 2014

Context. Herschel observations suggest that the H2O distribution in outflows from low-mass stars resembles the H-2 emission. It is still unclear which of the different excitation components that characterise the mid-and near-IR H-2 distribution is associated with H2O. Aims. The aim is to spectrally resolve the different excitation components observed in the H-2 emission. This will allow us to identify the H-2 counterpart associated with H2O and finally derive directly an H2O abundance estimate with respect to H-2. Methods. We present new high spectral resolution observations of H-2 0-0 S(4), 0-0 S(9), and 1-0 S(1) towards HH 54, a bright nearby shock region in the southern sky. In addition, new Herschel/HIFI H2O (2(12)-1(01)) observations at 1670 GHz are presented. Results. Our observations show for the first time a clear separation in velocity of the different H-2 lines: the 0-0 S(4) line at the lowest excitation peaks at -7 kms(-1), while the more excited 0-0 S(9) and 1-0 S(1) lines peak at -15 km s(-1). H2O and high-J CO appear to be associated with the H-2 0-0 S(4) emission, which traces a gas component with a temperature of 700-1000 K. The H2O abundance with respect to H-2 0-0 S(4) is estimated to be X(H2O) < 1.4 x 10(-5) in the shocked gas over an area of 13 ''. Conclusions. We resolve two distinct gas components associated with the HH 54 shock region at different velocities and excitations. This allows us to constrain the temperature of the H2O emitting gas (<= 1000 K) and to derive correct estimates of H2O abundance in the shocked gas, which is lower than what is expected from shock model predictions.

stars: formation

ISM: individual objects: HH 54

infrared: ISM

Herbig-Haro objects

ISM: jets and outflows


G. Santangelo

Osservatorio Astronomico di Roma

Arcetri Astrophysical Observatory

S. Antoniucci

Osservatorio Astronomico di Roma

B. Nisini

Osservatorio Astronomico di Roma

C. Codella

Arcetri Astrophysical Observatory

Per Bjerkeli

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

T. Giannini

Osservatorio Astronomico di Roma

A. Lorenzani

Arcetri Astrophysical Observatory

L. K. Lundin

European Southern Observatory (ESO)

S. Cabrit

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

L. Calzoletti

René Liseau

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

D. A. Neufeld

Johns Hopkins University

M. Tafalla

E. F. van Dishoeck

Max Planck Society

Leiden University

Astronomy and Astrophysics

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

Vol. 569 Art. no. L8- 24748

Subject Categories

Astronomy, Astrophysics and Cosmology



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