Revisiting the solid HDO/H$_\mathsf{2}$O abundances

Dartois, E.; Thi, Wing-Fai; Geballe, T. R.; Deboffle, D.; d’Hendecourt, Louis Le Sergeant; Dishoeck, Ewine van

doi:10.1051/0004-6361:20021558

Cited by 68 publications

(89 citation statements)

References 36 publications

(32 reference statements)

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“…With a 3σ uncertainty, the water fractionation could be similar throughout the cloud with a HDO/H 2 O ratio between 1.4% and 5.8% in the inner part and between 0.2% and 2.2% in the outer part. Also the HDO/H 2 O ratio obtained here is in agreement with the upper limits of solid HDO/H 2 O (from 0.5% to 2%) determined by observations of OH and OD stretch bands in four low-mass protostars (Dartois et al 2003;Parise et al 2003).…”

Section: Discussionsupporting

confidence: 90%

“…The collapse should already have started to allow the CO molecules to freezeout and form formaldehyde and methanol at the grain surface. On the contrary, water would form at low densities in the early stages of the star formation before the protostellar collapse, as suggested by Dartois et al (2003) and Parise et al (2003). This is also consistent with the fact that H 2 O ices appear at relatively low extinction in the direction of the Taurus cloud (e.g.…”

Section: Discussionsupporting

confidence: 80%

“…This ratio has also been estimated in the inner envelope of low-mass protostars such as IRAS 16293-2422 (Parise et al 2005) at about 3%, NGC 1333-IRAS4B (Jørgensen & van Dishoeck 2010) with an upper limit of 0.06%, and NGC 1333-IRAS2A (Liu et al 2011) with a lower limit of 1%. Deuterated water has also been sought in ices towards several protostars, and has allowed Dartois et al (2003) and Parise et al (2003) to obtain upper limits of solid HDO/H 2 O from 0.5% to 2%.…”

Section: Introductionmentioning

confidence: 99%

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A study of deuterated water in the low-mass protostar IRAS 16293-2422

Coutens¹,

Vastel²,

Caux³

et al. 2012

A&A

131

236

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Context. Water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. To understand the evolution of water from the first stages of star formation to the formation of planets and comets, the HDO/H 2 O ratio is a powerful diagnostic. Aims. Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS 16293-2422 and learn more about the water formation mechanisms by determining the HDO/H 2 O abundance ratio. Results. It is the first time that so many HDO and H 182 O transitions have been detected towards the same source with high spectral resolution. We derive an inner HDO abundance (T ≥ 100 K) of about 1.7 × 10 −7 and an outer HDO abundance (T < 100 K) of about 8 × 10 −11 . To reproduce the HDO absorption lines observed at 894 and 465 GHz, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. At a 3σ uncertainty, the HDO/H 2 O ratio is 1.4-5.8% in the hot corino, whereas it is 0.2-2.2% in the outer envelope. It is estimated at ∼4.8% in the added absorbing layer. Conclusions. Although it is clearly higher than the cosmic D/H abundance, the HDO/H 2 O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similarity of the ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol, which formed later once the CO molecules had depleted on the grains.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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A study of deuterated water in the low-mass protostar IRAS 16293-2422

Coutens¹,

Vastel²,

Caux³

et al. 2012

A&A

131

236

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“…This has been explained by the fact that water ice is formed at an early stage when CO depletion is not marked. Observations of the O-H and O-D stretching bands in the infrared have provided upper limits of ∼1% for the solid HDO * /H 2 O * ratio towards intermediatemass and low-mass protostars (Parise et al 2003;Dartois et al 2003). The O-D band at 4.1 μm is weak and broad.…”

Section: Observational Constraints On the Hdo * Abundancementioning

confidence: 99%

HD depletion in starless cores

Sipilä

Caselli

Harju

2013

A&A

102

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Aims. We aim to investigate the abundances of light deuterium-bearing species such as HD, H 2 D + , and D 2 H + in a gas-grain chemical model that includes an extensive description of deuterium and spin-state chemistry, in physical conditions appropriate to the very centers of starless cores. Methods. We combined a gas-grain chemical model with radiative transfer calculations to simulate density and temperature structure in starless cores. The chemical model includes new reaction sets for both gas phase and grain surface chemistry, including deuterated forms of species with up to four atoms and the spin states of the light species H 2 , H + 2 , and H + 3 and their deuterated forms. Results. We find that in the dense and cold environments attributed to the centers of starless cores, HD eventually depletes from the gas phase because deuterium is efficiently incorporated into grain-surface HDO, resulting in inefficient HD production on grains for advanced core ages. HD depletion has consequences not only on the abundances of, e.g., H 2 D + and D 2 H + , whose production depends on the abundance of HD, but also on the spin state abundance ratios of the various light species, when compared with the complete depletion model where heavy elements do not influence the chemistry. Conclusions. While the eventual HD depletion leads to the disappearance of light deuterium-bearing species from the gas phase on a relatively short timescale at high density, we find that at late stages of core evolution, the abundances of H 2 D + and D 2 H + increase toward the core edge, and the distributions become extended. The HD depletion timescale increases if less oxygen is initially present in the gas phase, owing to chemical interaction between the gas and the dust preceding the starless core phase. Our results are greatly affected if H 2 is allowed to tunnel on grain surfaces, and therefore more experimental data is needed not only on tunneling but also on the O + H 2 surface reaction in particular.

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“…Singly deuterated water has also been studied in ices. Only upper limits between 5 × 10 −3 and 2 × 10 −2 have been determined (Parise et al 2003;Dartois et al 2003), which do not allow us to conclude on rather high (∼10 −2 ) or low ( < ∼ 10 −3 ) HDO/H 2 O ratios in grain mantles. Even if it is not possible to disentangle the emission from the hot corino (defined as the warm inner part of the envelope in which complex organic species are detected; Bottinelli et al 2004) and the outer envelope using single-dish telescopes, these observations can be extremely helpful to constrain the HDO/H 2 O ratio in the outer part of the protostellar envelopes (T < 100 K).…”

Section: Introductionmentioning

confidence: 99%

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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Revisiting the solid HDO/H$_\mathsf{2}$O abundances

Cited by 68 publications

References 36 publications

A study of deuterated water in the low-mass protostar IRAS 16293-2422

A study of deuterated water in the low-mass protostar IRAS 16293-2422

HD depletion in starless cores

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

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