O[TINF]2[/TINF] in Interstellar Molecular Clouds

Goldsmith, Paul F.; Melnick, Gary J.; Bergin, Edwin A.; Howe, J. E.; Snell, R. L.; Neufeld, David A.; Harwit, Martin; Ashby, M. L. N.; Patten, B. M.; Kleiner, S. C.; Plume, R.; Stauffer, J. R.; Tolls, Volker; Wang, Z.; Zhang, Y. F.; Erickson, N. R.; Koch, David; Schieder, R.; Winnewisser, G.; Chin, G.

doi:10.1086/312854

Cited by 111 publications

(87 citation statements)

References 29 publications

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“…Gibb & Little 1998;Willacy et al 1998;Caselli et al 1999;Kramer et al 1999) indicate that depletion may often become important at low enough densities that n(O) does not exceed about 1 cm −3 . The failure to detect O 2 and H 2 O features towards dense cores in low mass star forming regions (Goldsmith et al 2000;Snell et al 2000) provides further evidence of low gas phase abundances of elemental oxygen in many regions with n H not hugely in excess of 10 4 cm −3 . In short, in many circumstances the surface chemistry may well have evolved far towards completion without n(O) ever rising above 1 cm −3 , which is the typical value of n(H) in dark gas subjected to cosmic ray induced ionization at the standard rate of about 1 × 10 −17 s −1 .…”

Section: Resultsmentioning

confidence: 99%

A stochastic approach to grain surface chemical kinetics

Green

Toniazzo

Pilling

et al. 2001

A&A

148

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Abstract. A stochastic model of grain surface chemistry, based on a master equation description of the probability distributions of reactive species on grains, is developed. For an important range of conditions, rates of molecule formation are limited by low accretion rates, so that the probability that a grain contains more than one reactive atom or molecule is small. We derive simple approximate expressions for these circumstances, and explore their validity through comparison with numerical solutions of the master equation for H, O and H, N, O reaction systems. A more detailed analysis of the range of validity of several analytic approximations and numerical solutions, based on exact analytical results for a model in which H and H2 are the only species, is also made. Though the use of our simple approximate expressions is computationally efficient, the solution of the master equation under the assumption that no grain contains more than two particles of each species usually gives more accurate results in the parameter regimes where the deterministic rate equation approach is inappropriate. The implementation of sparse matrix inversion techniques makes the use of such a truncated master equation solution method feasible for considerably more complicated surface chemistries than the ones we have examined here.

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Section: Resultsmentioning

confidence: 99%

A stochastic approach to grain surface chemical kinetics

Green

Toniazzo

Pilling

et al. 2001

A&A

148

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“…The C 18 O column density varies by less than 20% for 20 K ≤ T kin ≤ 50 K. Assuming that C 18 O/H 2 = 1.5 × 10 −7 (likely within about 30%, e.g. Wannier et al 1976;Goldsmith et al 2000), H 2 columns are found to be 1 × 10 23 cm −2 .…”

Section: O 2 Abundancementioning

confidence: 93%

“…It is therefore surprising that O 2 has been detected only toward the dense cloud core ρ Oph A (Larsson et al 2007, and this work) and a spot in OMC-1 (Goldsmith et al 2011), despite numerous searches toward other regions. For instance, surveying twenty sources, Goldsmith et al (2000) obtained limiting O 2 abundances N(O 2 )/N(H 2 ) of a few times 10 −7 , whereas Pagani et al (2003) derived upper limits to the O 2 column density of 10 15 to a few times 10 16 cm −2 for nearly a dozen objects. These surveys included dark clouds, regions of low-mass star formation in the solar neighbourhood and of high-mass star formation at different galactocentric distances, i.e.…”

Section: Source(s) Of O 2 or The Dearth Of Omentioning

confidence: 99%

“…The historical account of this essentially fruitless "O 2 -struggle" was reviewed by Goldsmith et al (2011). Prior to Herschel, both SWAS Goldsmith et al 2000) and Odin (Nordh et al 2003;Pagani et al 2003) had already shown that the abundances of both O 2 and H 2 O assumed by Goldsmith & Langer (1978) were much higher than actual values in the ISM and, with the exception of the ρ Oph cloud, none of the O 2 lines were detected anywhere Based on observations with Herschel-HIFI. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.…”

Section: Introductionmentioning

confidence: 99%

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Multi-line detection of O₂towardρOphiuchi A

Liseau

Goldsmith

Larsson

et al. 2012

A&A

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Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O 2 , and water, H 2 O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O 2 in the dense star-forming interstellar medium. Aims. Only toward ρ Oph A did Odin detect a very weak line of O 2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O 2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O 2 spectra toward selected positions in the ρ Oph A core. These data are analysed using standard techniques for O 2 excitation and compared to recent PDR-like chemical cloud models.Results. The N J = 3 3 −1 2 line at 487.2 GHz is clearly detected toward all three observed positions in the ρ Oph A core. In addition, an oversampled map of the 5 4 −3 4 transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O 2 emitting gas appears to vary quite substantially, with warm gas ( > ∼ 50 K) being adjacent to a much colder region, of temperatures lower than 30 K. Conclusions. The exploited models predict that the O 2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O 2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O 2 ) = 3 to > ∼ 6 × 10 15 cm −2 . Beam-averaged O 2 abundances are about 5 × 10 −8 relative to H 2 . Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire ρ Oph A core. We speculate that one of the reasons for the generally very low detection rate of O 2 is the short period of time during which O 2 molecules are reasonably abundant in molecular clouds.

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“…Goldsmith et al 2000;Pagani et al 2003), with the definite detection of the molecule in merely two sources, viz. ρ Oph A (Larsson et al 2007;Liseau et al 2012) and Orion A (Goldsmith et al 2011;Chen et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Search for HOOH in Orion

Liseau

Larsson

2015

A&A

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Context. The abundance of key molecules determines the level of cooling that is necessary for the formation of stars and planetary systems. In this context, one needs to understand the details of the time dependent oxygen chemistry, leading to the formation of O 2 and H 2 O. Aims. We aim to determine the degree of correlation between the occurrence of O 2 and HOOH (hydrogen peroxide) in star-forming molecular clouds. We first detected O 2 and HOOH in ρ Oph A, we now search for HOOH in Orion OMC A, where O 2 has also been detected. Methods. We mapped a 3 × 3 region around Orion H 2 -Peak 1 with the Atacama Pathfinder Experiment (APEX). In addition to several maps in two transitions of HOOH, viz. 219.17 GHz and 251.91 GHz, we obtained single-point spectra for another three transitions towards the position of maximum emission. Results. Line emission at the appropriate LSR-velocity (Local Standard of Rest) and at the level of ≥4σ was found for two transitions, with lower signal-to-noise ratio (2.8−3.5σ) for another two transitions, whereas for the remaining transition, only an upper limit was obtained. The emitting region, offset 18 south of H 2 -Peak 1, appeared point-like in our observations with APEX. Conclusions. The extremely high spectral line density in Orion makes the identification of HOOH much more difficult than in ρ Oph A. As a result of having to consider the possible contamination by other molecules, we left the current detection status undecided.

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O[TINF]2[/TINF] in Interstellar Molecular Clouds

Cited by 111 publications

References 29 publications

A stochastic approach to grain surface chemical kinetics

A stochastic approach to grain surface chemical kinetics

Multi-line detection of O₂towardρOphiuchi A

Search for HOOH in Orion

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O[TINF]2[/TINF] in Interstellar Molecular Clouds

Cited by 111 publications

References 29 publications

A stochastic approach to grain surface chemical kinetics

A stochastic approach to grain surface chemical kinetics

Multi-line detection of O2towardρOphiuchi A

Search for HOOH in Orion

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Product

Resources

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Multi-line detection of O₂towardρOphiuchi A