Herschel HIFI observations of O${}_2$ toward Orion: special conditions for shock enhanced emission

Abstract

We report observations of molecular oxygen (O${}_2$) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O${}_2$ emission is 9" (6e16 cm) in size, and is located close to the H2 Peak 1position (where vibrationally-excited H${}_2$ emission peaks), and not at Peak A, 23" away. The peak O2 column density is 1.1e18/cm2. The line velocity is close to that of 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line-of-sight. The enhanced O${}_2$ abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C-shock through a clump with preshock density 2e4/cm3, if a reasonable flux of UV radiation is present. The postshock O${}_2$ can explain the emission from the source if its line of sight dimension is ~10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O${}_2$ emission has not been detected in the cores of other massive star-forming molecular clouds.

arXiv comment28 pages, 13 figures

References in corpus (28)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• A computer program for fast non-LTE analysis of interstellar line spectra
• The distance to the Orion Nebula
• Water, O2 and Ice in Molecular Clouds
• Evaporation of ices near massive stars: models based on laboratory TPD data
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Herschel Measurements of Molecular Oxygen in Orion
• Parametrization of C-shocks. Evolution of the Sputtering of Grains
• Molecular oxygen in the rho Ophiuchi cloud
• Herschel observations of EXtra-Ordinary Sources: Analysis of the HIFI 1.2 THz Wide Spectral Survey Toward Orion KL I. Methods
• Explosive Outflows Powered by the Decay of Non-Hierarchical Multiple Systems of Massive Stars: Orion BN/KL
• Multi-line detection of O2 toward rho Oph A
• APEX-CHAMP+ high-J CO observations of low-mass young stellar objects: I. The HH 46 envelope and outflow
• A Multi-Epoch Study of the Radio Continuum Emission of Orion Source I: Constraints on the Disk Evolution of a Massive YSO and the Dynamical History of Orion BN/KL
• L1157-B1: Water and ammonia as diagnostics of shock temperature
• A line confusion-limited millimeter survey of Orion KL. III. Sulfur oxide species
• Estimation and reduction of the uncertainties in chemical models: Application to hot core chemistry
• Unveiling Sources of Heating in the Vicinity of the Orion BN/KL Hot Core as Traced by Highly Excited Inversion Transitions of Ammonia
• Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the SMA
• Deep observations of O2 toward a low-mass protostar with Herschel-HIFI
• Grain Destruction in Interstellar Shocks
• Temporal evolution of magnetic molecular shocks I. Moving grid simulations
• Deuterated molecules in Orion KL from Herschel/HIFI
• Herschel Search for O2 Toward the Orion Bar
• Temporal evolution of magnetic molecular shocks II. Analytics of the steady state and semi-analytical construction of intermediate ages
• The APEX-CHAMP+ view of the Orion Molecular Cloud 1 core - Constraining the excitation with submillimeter CO multi-line observations
• A 3D view of the outflow in the Orion Molecular Cloud 1 (OMC-1)
• Herschel/HIFI observations of a new interstellar water maser: the 5(32)-4(41) transition at 620.701 GHz

Cited by in corpus (22)

• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Velocity-resolved [CII] emission and [CII]/FIR Mapping along Orion with Herschel
• A primordial origin for molecular oxygen in comets: A chemical kinetics study of the formation and survival of O${}_2$ ice from clouds to disks
• Herschel Far-Infrared Spectral-mapping of Orion BN/KL Outflows: Spatial distribution of excited CO, H2O, OH, O and C+ in shocked gas
• A New Determination of the Binding Energy of Atomic Oxygen on Dust Grain Surfaces: Experimental Results and Simulations
• Linking interstellar and cometary O${}_2$: a deep search for ${}^{16}$O${}^{18}$O in the solar-type protostar IRAS 16293--2422
• Nitrogen oxide in protostellar envelopes and shocks: the ASAI survey
• A Search for O_2 in CO-depleted Molecular Cloud Cores with Herschel
• Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM II. Molecular oxygen abundance
• The Orion fingers: Near-IR spectral imaging of an explosive outflow
• Molecular tracers of radiative feedback in Orion (OMC-1). Widespread CH+ (J=1-0), CO (10-9), HCN (6-5), and HCO+ (6-5) emission
• Herschel HIFI Observations of the Sgr A +50 km/s Cloud. Deep Searches for O2 in Emission and Foreground Absorption
• Cosmic-ray-induced dissociation and reactions in warm interstellar ices
• A First Look for Molecules between 103 and 133 MHz using the Murchison Widefield Array
• Molecular Oxygen in the nearest QSO Mrk 231
• Distribution of Water Vapor in Molecular Clouds. II
• A new constraint on the molecular oxygen abundance at $z\sim 0.886$
• Dust temperature and time-dependent effects in the chemistry of photodissociation regions
• Atomic oxygen abundance toward Sagittarius B2
• Search for HOOH in Orion
• Self-generated ultraviolet radiation in molecular shock waves I. Effects of Lyman $\alpha$, Lyman $\beta$, and two-photon continuum
• Deep search for hydrogen peroxide toward pre- and protostellar objects -- Testing the pathway of grain surface water formation