The shocked gas of the BHR71 outflow observed by Herschel: indirect evidence for an atomic jet

Abstract

In the BHR71 region, two low-mass protostars drive two distinguishable outflows. They constitute an ideal laboratory to investigate the effects of shock chemistry and the mechanisms that led to their formation. We aim to define the morphology of the warm gas component of the BHR 71 outflow and at modelling its shocked component. We present the first far infrared Herschel images of the BHR71 outflow in the CO(14-13), H${}_2$O (2${}_{21}$-1${}_{10}$), H${}_2$O (2${}_{12}$-1${}_{01}$) and [OI] 145 $\mu$m, lines, revealing the presence of several knots of warm, shocked gas associated with fast outflowing gas. In two of these knots we performed a detailed study of the physical conditions by comparing a large set of transitions from several molecules to a grid of shock models. Herschel lines ratios in the outflow knots are quite similar, showing that the excitation conditions of the fast moving gas do not change significantly within the first $\sim$ 0.068 pc of the outflow, apart at the extremity of the southern blue-shifted lobe that is expanding outside the molecular cloud. Rotational diagram, spectral line profile and LVG analysis of the CO lines in knot A show the presence of two gas components: one extended, cold ($T\sim$80 K) and dense ($n$(H${}_2$) = 3$\times$10${}^5$-4$\times$10${}^6$ cm${}^{-3}$) and another compact (18 arcsec), warm ($T$ = 1700-2200 K) with slightly lower density ($n$(H${}_2$) = (2-6)$\times$10${}^4$ cm${}^{-3}$). In the two brightest knots (where we performed shock modelling) we found that H${}_2$ and CO are well fitted with non-stationary (young) shocks. These models, however, significantly underestimate the observed fluxes of [OI] and OH lines, but are not too far off those of H${}_2$O, calling for an additional, possibly dissociative, J-type shock component. Our modelling indirectly suggests that an additional shock component exists, possibly a remnant of the primary jet

arXiv comment16 pages, 15 figures

References in corpus (28)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas
• The CHESS chemical Herschel surveys of star forming regions: Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
• Warm SiO gas in molecular bullets associated with protostellar outflows
• Spitzer spectral line mapping of protostellar outflows: I. Basic data and outflow energetics
• The CHESS survey of the L1157-B1 shock region: CO spectral signatures of jet-driven bowshocks
• Theoretical HDO emission from low-mass protostellar envelopes
• Infall and Outflow around the HH 212 protostellar system
• The clumpy structure of the chemically active L1157 outflow
• The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor
• On the excitation of the infrared knots along protostellar jets
• Spectroscopically resolved far-IR observations of the massive star-forming region G5.89--0.39
• ATCA and Spitzer Observations of the Binary Protostellar Systems CG30 and BHR71
• The CHESS survey of the L1157-B1 shock: the dissociative jet shock as revealed by Herschel--PACS
• IRAS 11590-6452 in BHR 71 - a binary protostellar system?
• Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha
• Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using Herschel-HIFI
• CO and CH3OH observations of the BHR71 outflows with APEX
• High-pressure, low-abundance water in bipolar outflows. Results from a Herschel-WISH survey
• Spitzer spectral line mapping of protostellar outflows: III - H_2 emission in L1448, BHR71, and NGC2071
• DIGIT: Herschel and Spitzer spectro-imaging of SMM3 and SMM4 in Serpens
• Revisiting the shocks in BHR71: new observational constraints and H2O predictions for Herschel
• Probing MHD Shocks with high-J CO observations: W28F
• APEX observations of supernova remnants - I. Non-stationary MHD-shocks in W44
• Impacts of pure shocks in the BHR71 bipolar outflow
• Herschel PACS observations of shocked gas associated with the jets of L1448 and L1157
• Resolving the shocked gas in HH54 with Herschel: CO line mapping at high spatial and spectral resolution

Cited by in corpus (5)

• ALMA observations of water deuteration: A physical diagnostic of the formation of protostars
• Nature of shocks revealed by SOFIA OI observations in the Cepheus E protostellar outflow
• ALMA Reveals A Collision Between Protostellar Outflows in BHR71
• H${}_2$ emission from non-stationary magnetized bow shocks
• Early Planet Formation in Embedded Disks (eDisk). XI. A high-resolution view toward the BHR 71 Class 0 protostellar wide binary