Herschel spectral-line mapping of the HH211 protostellar system

Abstract

(Abridged) Mid- and far-infrared observations of the environment around embedded protostars reveal a plethora of high excitation molecular and atomic emission lines. In this work we present spectro-imaging observations of the HH211 system with Herschel/PACS that record emission from major molecular (CO, H2O and OH) and atomic coolants (e.g. [OI]). Molecular lines are mainly exited at the terminal bowshocks of the outflow and around the position of the protostar. All lines show maxima at the southeast bowshock with the exception of water emission that peaks around the central source. Excitation analysis in all positions shows that CO and H${}_2$O are mainly thermally excited at T~ 350 K and 90 K respectively, with the CO showing a second temperature component at 750 K towards the southeast peak. Excitation analysis breaks down in the case of OH, indicating that the molecule is non-thermally excited. Comparisons between the CO and H2 column densities suggest that the CO abundance value in shocks can be up to an order of magnitude lower than the canonical value of 10${}^{-4}$. The water ortho-to-para ratio around the protostar is only 0.65, indicating low-temperature water ice formation followed by non-destructive photodesorption from the dust grains. Therefore the low ortho-to-para ratio in water that can be interpreted in terms of formation from a primordial gas reservoir in the protostellar envelope. The two-sided total atomic mass flux estimated from the [OI] jet sums to 1.65$\times 10^{-6}$ M${}_{\odot }$ yr${}^{-1}$, a value that is very close to the mass flux previously estimated for the SiO jet and the H${}_2$ outflow. These comparisons render HH211 the first embedded system where an atomic jet is demonstrably shown to possess enough momentum to drive the observed molecular jets and large scale outflows.

10 pages, 6 figures, Accepted for publication in Astronomy & Astrophysics

References in corpus (7)

• Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus
• Submillimeter arcsecond-resolution mapping of the highly collimated protostellar jet HH 211
• The Herschel-PACS legacy of low-mass protostars: Properties of warm and hot gas and its origin in far-UV illuminated shocks
• Discovery of superthermal hydroxyl (OH) in the HH211 outflow
• A Multi-Epoch SMA Study of the HH 211 Protostellar Jet: Jet Motion and Knot Formation
• A non-equilibrium ortho-to-para ratio of water in the Orion PDR
• The feedback of atomic jets from embedded protostars in NGC 1333

Cited by in corpus (10)

• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Jets from Young Stars
• OH mid-infrared emission as a diagnostic of H${}_2$O UV photodissociation. I. Model and application to the HH 211 shock
• JWST Observations of Young protoStars (JOYS): overview of program and early results
• JWST Observations of Young protoStars (JOYS). HH 211: the textbook case of a protostellar jet and outflow
• Feedback of molecular outflows from protostars in NGC 1333, revealed by Herschel and Spitzer spectro-imaging observations
• Probing the hidden atomic gas in Class I jets with SOFIA
• Evolution of the atomic component in protostellar outflows
• PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem
• Linking Young Stellar Object Morphology to Evolutionary Stages with Self-Organizing Maps