Oxygen in dense interstellar gas

Liseau, R.; Justtanont, K.

doi:10.1051/0004-6361/200811392

Cited by 14 publications

(24 citation statements)

References 48 publications

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“…A value of about 450 was found by Liseau et al (1995) for L 1688 using CS maps and 60 µm IRAS data. A high g2d would also be consistent with the low oxygen abundance in ρ Oph A found by Liseau & Justtanont (2009). Figure 11 of Brinchmann et al (2013), which is based on a large number of galaxies, supports this view on larger, extragalactic scales.…”

Section: Introductionsupporting

confidence: 76%

Gas and dust in the star-forming regionρ Oph A

Liseau

Larsson

Lunttila

et al. 2015

A&A

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Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N 2 H + , which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N 2 H + (J = 3−2) and (J = 6−5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H 2 ), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C 18 O, also N 2 H + is frozen onto the grains.

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Section: Introductionsupporting

confidence: 76%

Gas and dust in the star-forming regionρ Oph A

Liseau

Larsson

Lunttila

et al. 2015

A&A

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“…Observations of the fine structure components of O I at 63 µm ( 3 P 1 -3 P 2 ) and 145 µm ( 3 P 0 -3 P 1 ) of the inverted ground state with the ISO-LWS (Long Wavelength Spectrometer, Clegg et al 1996) towards the VLA 1623 outflow have been presented earlier by Liseau & Justtanont (2009). On OD 1202, the Photodetector Array Camera and Spectrometer (PACS, Poglitsch et al 2010) was used to map the fine structure line emission north of the outflow (see Fig.…”

Section: O Imentioning

confidence: 89%

“…To estimate the absolute accuracy of the fluxes we compared data from one map position with those that we previously obtained with the ISO-LWS (e.g. Liseau & Justtanont 2009). However, we refer here to re-reduced data using the final version of the pipeline (OLP 10).…”

Section: O Imentioning

confidence: 99%

Gas and dust in the star-forming regionρOph A

Larsson

Liseau

2017

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Context. The evolution of interstellar clouds of gas and dust establishes the prerequisites for star formation. The pathway to the formation of stars can be studied in regions that have formed stars, but which at the same time also display the earliest phases of stellar evolution, i.e. pre-collapse/collapsing cores (Class-1), protostars (Class 0), and young stellar objects (Class I, II, III). Aims. We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. Methods. ρ Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H 2 , H 2 O, NH 3 , N 2 H + , O 2 , O I, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in ρ Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H 2 O and NH 3 , where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. Results. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and O I are seen throughout the region around the exciting star S 1. At the interface to the molecular core 0.05 pc away, atomic hydrogen is rapidly converted into H 2 , whereas O I protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O 2 in the core SM 1, where X(O 2) ∼ 5 × 10 −8. There, the ratio of the O 2 to H 2 O abundance [X(H 2 O) ∼ 5 × 10 −9 ] is significantly higher than unity. Away from the core, O 2 experiences a dramatic decrease due to increasing H 2 O formation. Outside the molecular core ρ Oph A, on the far side as seen from S 1, the intense radiation from the 0.5 pc distant early B-type star HD 147889 destroys the molecules. Conclusions. Towards the dark core SM 1, the observed abundance ratio X(O 2)/X(H 2 O) > 1, which suggests that this object is extremely young, which would explain why O 2 is such an elusive molecule outside the solar system.

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“…Summarizing the main results of this analysis, Nisini et al (2015) find that while the density of colliders is rather well constrained (ranging between 10 4 − 10 5 cm −3 ), the nature of the colliders (atomic or molecular hydrogen) can affect the 63µm [O i] emissivity by a factor ranging between 2 and 5. In an order study, Liseau & Justtanont (2009) demonstrated that the emissivity of the 63 µm line can vary up to a factor of three for kinetic temperatures higher than 300 K, while in the same study they find that the excitation of the [O i] 63 µm line typically traces kinetic temperatures of ∼ 1000 K.…”

Section: Mass Momentum and Energymentioning

confidence: 94%

Feedback of atomic jets from embedded protostars in NGC 1333

Dionatos

Güdel

2016

A&A

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Abridged] Star-formation feedback onto the parent cloud is conventionally examined through the study of molecular outflows. Little is however known on the effect that atomic ejecta, tracing fast shocks, can have on the global cloud properties. In this study we employ Herschel/PACS [O i] and [C ii] spectral line maps of the NGC 1333 star-forming region to assess the relative influence of atomic jets onto the star-formation process. Atomic line maps are compared against molecular outflow tracers and atomic ejecta are associated to individual driving sources. We study the detailed morphology and velocity distribution of [O i] line using channel and line-centroid maps and derive the momentum, energy, and mass flux for all the bipolar jets traced by [O i] line emission. We find that the line-centroid maps can trace velocity structures down to 5 km s −1 which is a factor of ∼20 beyond the nominal velocity resolution reached by Herschel/PACS. These maps reveal an unprecedented degree of details that assist significantly in the association and characterization of jets and outflows. Comparisons of the dynamical and kinematical properties shows that [O i] momentum accounts for only ∼1% of the momentum carried by the large scale CO outflows but the energy released through the jets corresponds to 50 -100% of the energy released in outflows. The estimated ratios of the jet to the outflow momenta and energies are consistent with the results of two-component, nested jet/outflow simulations, where jets are associated to episodic accretion events. Under this scenario, the energy from atomic jets to the cloud is as important as the energy output from outflows in maintaining turbulence and dissipating the cloud gas.

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Oxygen in dense interstellar gas

Cited by 14 publications

References 48 publications

Gas and dust in the star-forming regionρ Oph A

Gas and dust in the star-forming regionρ Oph A

Gas and dust in the star-forming regionρOph A

Feedback of atomic jets from embedded protostars in NGC 1333

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