Deep observations of O<sub>2</sub>toward a low-mass protostar with<i>Herschel</i>-HIFI

Yıldız, U. A.; Acharyya, Kinsuk; Goldsmith, Paul F.; Dishoeck, E. F. van; Melnick, Gary J.; Snell, R. L.; Liseau, R.; Chen, Jo-Hsin; Pagani, L.; Bergin, Edwin A.; Caselli, P.; Herbst, Eric; Kristensen, L. E.; Visser, R.; Lis, D.; Gérin, M.

doi:10.1051/0004-6361/201321944

Cited by 64 publications

(86 citation statements)

References 82 publications

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“…The time that the cloud spends A81, page 12 of 19 in this low density phase is unknown, but it would only add to the amount of water ice after the pre-collapse phase, exacerbating the need for a short dense, prestellar phase. Our short inferred pre-stellar phase is in contrast with Yıldız et al (2013b) who argued for a long prestellar phase of at least 1 Myr at n H = 10 5 cm −3 to explain the absence of gas-phase O 2 toward the NGC 1333 IRAS4A protostellar core. Since water ice is not observed directly toward this core, it is not clear whether there is a similar discrepancy.…”

Section: Water Icecontrasting

confidence: 99%

Water in low-mass star-forming regions withHerschel

Schmalzl

Visser

Walsh

et al. 2014

A&A

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Aims. Our aim is to determine the critical parameters in water chemistry and the contribution of water to the oxygen budget by observing and modelling water gas and ice for a sample of eleven low-mass protostars, for which both forms of water have been observed. Methods. A simplified chemistry network, which is benchmarked against more sophisticated chemical networks, is developed that includes the necessary ingredients to determine the water vapour and ice abundance profiles in the cold, outer envelope in which the temperature increases towards the protostar. Comparing the results from this chemical network to observations of water emission lines and previously published water ice column densities, allows us to probe the influence of various agents (e.g., far-ultraviolet (FUV) field, initial abundances, timescales, and kinematics). Results. The observed water ice abundances with respect to hydrogen nuclei in our sample are 30−80 ppm, and therefore contain only 10-30% of the volatile oxygen budget of 320 ppm. The keys to reproduce this result are a low initial water ice abundance after the pre-collapse phase together with the fact that atomic oxygen cannot freeze-out and form water ice in regions with T dust > ∼ 15 K. This requires short prestellar core lifetimes < ∼ 0.1 Myr. The water vapour profile is shaped through the interplay of FUV photodesorption, photodissociation, and freeze-out. The water vapour line profiles are an invaluable tracer for the FUV photon flux and envelope kinematics. Conclusions. The finding that only a fraction of the oxygen budget is locked in water ice can be explained either by a short precollapse time of < ∼ 0.1 Myr at densities of n H ∼ 10 4 cm −3 , or by some other process that resets the initial water ice abundance for the post-collapse phase. A key for the understanding of the water ice abundance is the binding energy of atomic oxygen on ice.

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Section: Water Icecontrasting

confidence: 99%

Water in low-mass star-forming regions withHerschel

Schmalzl

Visser

Walsh

et al. 2014

A&A

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“…Alternatively, the material could be trapped in grain mantles in the form of atomic Si; the Si would then be desorbed and react with O 2 or OH to form SiO according to the following reactions (Walmsley et al 1999 The balance between photodesorption and photodissociation predicts an SiO-enriched layer located at some depth behind the photodissociation front, which can easily explain the SiO column density observed towards the Orion Bar of a few 10 12 cm −2 (Walmsley et al 1999;Schilke et al 2001). Although O 2 is actually less abundant than assumed in these early models, a tentative detection of O 2 was recently reported towards IRAS 4A at a velocity (∼8.0 km s −1 ) close to our HDO absorptions (∼7.6 km s −1 ), and suggested to be produced by photodesorption mechanisms (Yıldız et al 2013). Photodissociation of H 2 O would also produce ample OH to react with Si and form SiO by the second reaction above.…”

Section: B1 Photodesorptionsupporting

confidence: 69%

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Coutens

Vastel

Cabrit

et al. 2013

A&A

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Context. The measure of the water deuterium fractionation is a relevant tool for understanding mechanisms of water formation and evolution from the prestellar phase to the formation of planets and comets. Aims. The aim of this paper is to study deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B, to compare their HDO abundance distributions with other star-forming regions, and to constrain their HDO/H 2 O abundance ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based telescopes, we observed several HDO lines covering a large excitation range (E up /k = 22-168 K) towards these protostars and an outflow position. Non-local thermal equilibrium radiative transfer codes were then used to determine the HDO abundance profiles in these sources. Results. The HDO fundamental line profiles show a very broad component, tracing the molecular outflows, in addition to a narrower emission component and a narrow absorbing component. In the protostellar envelope of NGC 1333 IRAS 4A, the HDO inner (T ≥ 100 K) and outer (T < 100 K) abundances with respect to H 2 are estimated with a 3σ uncertainty at 7.5 +3.5 −3.0 × 10 −9 and 1.2 +0.4 −0.4 × 10 −11 , respectively, whereas in NGC 1333 IRAS 4B they are 1 +1.8 −0.9 × 10 −8 and 1.2 +0.6 −0.4 × 10 −10 , respectively. Similarly to the low-mass protostar IRAS 16293-2422, an absorbing outer layer with an enhanced abundance of deuterated water is required to reproduce the absorbing components seen in the fundamental lines at 465 and 894 GHz in both sources. This water-rich layer is probably extended enough to encompass the two sources, as well as parts of the outflows. In the outflows emanating from NGC 1333 IRAS 4A, the HDO column density is estimated at about (2-4) × 10 13 cm −2 , leading to an abundance of about (0.7-1.9) × 10 −9 . An HDO/H 2 O ratio between 7 × 10 −4 and 9 × 10 −2 is also derived in the outflows. In the warm inner regions of these two sources, we estimate the HDO/H 2 O ratios at about 1 × 10 −4 -4 × 10 −3 . This ratio seems higher (a few %) in the cold envelope of IRAS 4A, whose possible origin is discussed in relation to formation processes of HDO and H 2 O. Conclusions. In low-mass protostars, the HDO outer abundances range in a small interval, between ∼10 −11 and a few 10 −10 . No clear trends are found between the HDO abundance and various source parameters (L bol , L smm , L smm /L bol , T bol , L 0.6 bol /M env ). A tentative correlation is observed, however, between the ratio of the inner and outer abundances with the submillimeter luminosity.

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“…The success story of combined laboratory and observational studies became complete with the detection of gas-phase HO 2 199 Interestingly, ρ Oph A is also one of only two positions where interstellar O 2 gas has been firmly detected through multi-line observations with the Odin and Herschel satellites 202,203 . Deep limits in other cold cores confirm the scenario in which most of the O and O 2 must be converted into H 2 O ice on the grains before the protostar starts to heat its surroundings 204,205 . Perhaps the grain temperature in ρ Oph A, around 30 K, is just optimal to prevent atomic oxygen from freezing out and being converted into water ice.…”

Section: H 2 O O 2 and The Importance Of Solid-state Chemistrymentioning

confidence: 57%

Astrochemistry of dust, ice and gas: introduction and overview

Dishoeck

Ewine²

2014

Faraday Discuss.

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102

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A brief introduction and overview of the astrochemistry of dust, ice and gas and their interplay is presented, aimed at non-specialists. The importance of basic chemical physics studies of critical reactions is illustrated through a number of recent examples. Such studies have also triggered new insight into chemistry, illustrating how astronomy and chemistry can enhance each other. Much of the chemistry in star- and planet-forming regions is now thought to be driven by gas-grain chemistry rather than pure gas-phase chemistry, and a critical discussion of the state of such models is given. Recent developments in studies of diffuse clouds and PDRs, cold dense clouds, hot cores, protoplanetary disks and exoplanetary atmospheres are summarized, both for simple and more complex molecules, with links to papers presented in this volume. In spite of many lingering uncertainties, the future of astrochemistry is bright: new observational facilities promise major advances in our understanding of the journey of gas, ice and dust from clouds to planets.Comment: Introductory paper for Faraday Discussions 168 conference, April 201

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Deep observations of O₂toward a low-mass protostar withHerschel-HIFI

Cited by 64 publications

References 82 publications

Water in low-mass star-forming regions withHerschel

Water in low-mass star-forming regions withHerschel

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Astrochemistry of dust, ice and gas: introduction and overview

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Deep observations of O2toward a low-mass protostar withHerschel-HIFI

Cited by 64 publications

References 82 publications

Water in low-mass star-forming regions withHerschel

Water in low-mass star-forming regions withHerschel

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Astrochemistry of dust, ice and gas: introduction and overview

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Product

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Deep observations of O₂toward a low-mass protostar withHerschel-HIFI