A SEARCH FOR O<sub>2</sub> IN CO-DEPLETED MOLECULAR CLOUD CORES WITH HERSCHEL

Wirström, E. S.; Charnley, Steven B.; Cordiner, Martin; Ceccarelli, C.

doi:10.3847/0004-637x/830/2/102

Cited by 15 publications

(13 citation statements)

References 62 publications

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“…Of considerable interest is to understand the formation history of O 2 in ρ Oph A as this molecule, in spite of numerous attempts (Goldsmith et al 2000(Goldsmith et al , 2002Pagani et al 2003;Yıldız et al 2013;Sandqvist et al 2015;Wirström et al 2016), has hardly been found anywhere else outside the solar system. Taking into account new lab results for the oxygen binding energy on dust grains (He et al 2015), Taquet et al (2016) recently discussed a number of formation scenarios and argued in favour of a particular one that could fit the physical conditions in ρ Oph A.…”

Section: Abundant O 2 Production In ρ Oph Amentioning

confidence: 99%

Gas and dust in the star-forming regionρOph A

Larsson

Liseau

2017

A&A

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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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Section: Abundant O 2 Production In ρ Oph Amentioning

confidence: 99%

Gas and dust in the star-forming regionρOph A

Larsson

Liseau

2017

A&A

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“…reflecting the abundances in the nascent molecular clouds from which the comets formed) then the high O2 abundances that are detected in comet 67P/C-G would seem to be at odds with both observations and (equilibrium) astrochemical models; which predict O2 abundances of at least an order of magnitude lower in dark clouds than these values (e.g. Wirström, Charnley, Cordiner & Ceccarelli 2016), although there may be an obvious reason for this -as discussed above.…”

Section: A Primordial Origin For the O2mentioning

confidence: 94%

“…Yildiz et al 2013) have found that the depletion of O-atoms by freeze-out and conversion to H2O and/or the destruction of O2 by C-atoms (before CO formation is complete) yields low values of the O2 abundance -typically an order of magnitude or more smaller than what is found in comet 67P/C-G. However, these models also show that the O2 abundance rises significantly after the efficient conversion of C to CO has occurred (Wirström, Charnley, Cordiner & Ceccarelli 2016). Moreover, the models also assume that the freeze-out of O-atoms and conversion to H2O, which is fully retained in the ices is efficient.…”

Section: A Gas-phase Primordial Origin Of O2mentioning

confidence: 98%

“…There are thus three competing timescales: O to O2 conversion, CO formation and O-atom freeze-out. Wirström, Charnley, Cordiner & Ceccarelli (2016) argue that, in dense cores where (a) CO conversion is complete and (b) the effective rate for O-atom freeze-out may be reduced if the chemical conversion of O to OH and H2O is inhibited due to the low abundance of atomic hydrogen; the O2 abundance might be significantly enhanced in transient peaks; the competing timescales resulting in significant chemical non-linearities. There is some evidence to suggest that large O/CO ratios may exist in dense, dark clouds (e.g.…”

Section: A Gas-phase Primordial Origin Of O2mentioning

confidence: 99%

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A gas-phase primordial origin of O2 in comet 67P/Churyumov-Gerasimenko

Rawlings

Wilson

Williams

2019

Monthly Notices of the Royal Astronomical Society

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Recent observations made by the Rosetta/ROSINA instrument have detected molecular oxygen in the coma of comet 67P/Churyumov-Gerasimenko with abundances at the 1-10% level relative to H 2 O. Previous studies have indicated that the likely origin of the O 2 may be surface chemistry of primordial (dark cloud) origin, requiring somewhat warmer, denser and extreme H-atom poor conditions than are usually assumed. In this study we propose a primordial gas-phase origin for the O 2 which is subsequently frozen and effectively hidden until the ice mantles are sublimated in the comet's coma. Our study presents results from a three-phase astrochemical model that simulates the chemical evolution of ices in the primordial dark cloud phase, its gravitational collapse, and evolution in the early protosolar nebula. We find that the O 2 abundance can be produced and is fairly robust to the choice of the free parameters. Good matches for the O 2 :H 2 O ratio and, to a lesser extent, the N 2 :CO and CO:H 2 O ratios are obtained, but the models significantly over-produce N 2 . We speculate that the low value of N 2 :O 2 that is observed is a consequence of the specific thermal history of the comet.

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“…However, O 2 is difficult to detect, and it is commonly believed that it is not a major repository of oxygen in molecular clouds. In only two sources has molecular oxygen been identified so far, namely ρ Oph A and Orion A (Larsson et al 2007;Liseau et al 2012;Goldsmith et al 2011;Chen et al 2014), and many further attempts to find it in the gas phase have failed (Goldsmith et al 2000;Melnick & Bergin 2005;Yildiz et al 2013;Wirström et al 2016), as did the attempts to find it in solid form (Van den Bussche et al 1999;Tielens 2000).…”

Section: Introductionmentioning

confidence: 99%

Deep search for hydrogen peroxide toward pre- and protostellar objects

Fuchs

Witsch

Herberth

et al. 2020

A&A

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Context. In the laboratory, hydrogen peroxide (HOOH) was proven to be an intermediate product in the solid-state reaction scheme that leads to the formation of water on icy dust grains. When HOOH desorbs from the icy grains, it can be detected in the gas phase. In combination with water detections, it may provide additional information on the water reaction network. Hydrogen peroxide has previously been found toward ρ Oph A. However, further searches for this molecule in other sources failed. Hydrogen peroxide plays a fundamental role in the understanding of solid-state water formation and the overall water reservoir in young stellar objects (YSOs). Without further HOOH detections, it is difficult to assess and develop suitable chemical models that properly take into account the formation of water on icy surfaces. Aims. The objective of this work is to identify HOOH in YSOs and thereby constrain the grain surface water formation hypothesis. Methods. Using an astrochemical model based on previous work in combination with a physical model of YSOs, the sources R CrA-IRS 5A, NGCC1333-IRAS 2A, L1551-IRS 5, and L1544 were identified as suitable candidates for an HOOH detection. Long integration times on the APEX 12m and IRAM 30m telescopes were applied to search for HOOH signatures in these sources. Results. None of the four sources under investigation showed convincing spectral signatures of HOOH. The upper limit for HOOH abundance based on the noise level at the frequency positions of this molecule for the source R CrA-IRS 5A was close to the predicted value. For NGC1333-IRAS 2A, L1544, and L1551-IRS 5, the model overestimated the hydrogen peroxide abundances. Conclusions. HOOH remains an elusive molecule. With only one secure cosmic HOOH source detected so far, namely ρ Oph A, the chemical model parameters for this molecule cannot be sufficiently well determined or confirmed in existing models. Possible reasons for the nondetections of HOOH are discussed.

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A SEARCH FOR O₂ IN CO-DEPLETED MOLECULAR CLOUD CORES WITH HERSCHEL

Cited by 15 publications

References 62 publications

Gas and dust in the star-forming regionρOph A

Gas and dust in the star-forming regionρOph A

A gas-phase primordial origin of O2 in comet 67P/Churyumov-Gerasimenko

Deep search for hydrogen peroxide toward pre- and protostellar objects

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A SEARCH FOR O2 IN CO-DEPLETED MOLECULAR CLOUD CORES WITH HERSCHEL

Cited by 15 publications

References 62 publications

Gas and dust in the star-forming regionρOph A

Gas and dust in the star-forming regionρOph A

A gas-phase primordial origin of O2 in comet 67P/Churyumov-Gerasimenko

Deep search for hydrogen peroxide toward pre- and protostellar objects

Contact Info

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A SEARCH FOR O₂ IN CO-DEPLETED MOLECULAR CLOUD CORES WITH HERSCHEL