Water in star-forming regions with Herschel (WISH) II. Evolution of 557 GHz 1(10)-1(01) emission in low-mass protostars
Artikel i vetenskaplig tidskrift, 2012

Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims. The first systematic survey of spectrally resolved water emission in 29 low-mass (L < 40 L-circle dot) protostellar objects is presented. The sources cover a range of luminosities and evolutionary states. The aim is to characterise the line profiles to distinguish physical components in the beam and examine how water emission changes with protostellar evolution. Methods. H2O was observed in the ground-state 1(10)-1(01) transition at 557 GHz (E-up/k(B) similar to 60 K) as single-point observations with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel in 29 deeply embedded Class 0 and I low-mass protostars. Complementary far-IR and sub-mm continuum data (including PACS data from our programme) are used to constrain the spectral energy distribution (SED) of each source. H2O intensities are compared to inferred envelope properties, e.g., mass and density, outflow properties and CO 3-2 emission. Results. H2O emission is detected in all objects except one (TMC1A). The line profiles are complex and consist of several kinematic components tracing different physical regions in each system. In particular, the profiles are typically dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows, not in the quiescent envelope. Several sources show multiple shock components appearing in either emission or absorption, thus constraining the internal geometry of the system. Furthermore, the components include inverse P-Cygni profiles in seven sources (six Class 0, one Class I) indicative of infalling envelopes, and regular P-Cygni profiles in four sources (three Class I, one Class 0) indicative of expanding envelopes. Molecular "bullets" moving at greater than or similar to 50 km s(-1) with respect to the source are detected in four Class 0 sources; three of these sources were not known to harbour bullets previously. In the outflow, the H2O/CO abundance ratio as a function of velocity is nearly the same for all line wings, increasing from 10(-3) at low velocities (< 5 km s(-1)) to greater than or similar to 10(-1) at high velocities (> 10 km s(-1)). The water abundance in the outer cold envelope is low, greater than or similar to 10(-10). The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears.


molecular outflows


protoplanetary disk

ISM: jets and outflows

serpens cloud core


young stellar objects

spitzer observations


continuum observations

ISM: molecules



stars: formation

protostellar envelopes


L. Kristensen

Leiden Observatory Research Institute

E. F. van Dishoeck

Max Planck-institutet

Leiden Observatory Research Institute

E. A. Bergin

University Michigan Ann Arbor

R. Visser

University Michigan Ann Arbor

U. A. Yildiz

Leiden Observatory Research Institute

I. San Jose-Garcia

Leiden Observatory Research Institute

J. K. Jorgensen

Niels Bohr Institute

G. J. Herczeg

Max Planck-institutet

D. Johnstone

University of Victoria

National Research Council Canada

S. F. Wampfler

Eidgenössische Technische Hochschule Zürich (ETH)

A. O. Benz

Eidgenössische Technische Hochschule Zürich (ETH)

S. Bruderer

Max Planck-institutet

S. Cabrit

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

P. Caselli

University of Leeds

Osservatorio Astrofisico Di Arcetri

S. Doty

Denison University

D. Harsono

Leiden Observatory Research Institute

F. Herpin

Universite de Bordeaux

Laboratoire d'Astrophysique de Bordeaux

M. R. Hogerheijde

Leiden Observatory Research Institute

A. Karska

Max Planck-institutet

T. A. van Kempen

Atacama Large Millimeter-submillimeter Array

Leiden Observatory Research Institute

René Liseau

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

B. Nisini

Osservatorio Astronomico di Roma

M. Tafalla

Observatorio Astronomico Nacional

F. F. S. van der Tak

University of Groningen, Kapteyn Astronomical Institute

SRON Netherlands Institute for Space Research

F. Wyrowski

Max Planck-institutet

Astronomy and Astrophysics

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

Vol. 542 A8


Astronomi, astrofysik och kosmologi