Deuterium chemistry of dense gas in the vicinity of low-mass and massive star-forming regions

Awad, Zainab; Viti, S.; Bayet, E.; Caselli, P.

doi:10.1093/mnras/stu1141

Cited by 17 publications

(23 citation statements)

References 77 publications

(101 reference statements)

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“…The collapse occurs over 10 6 yr. During this time, gas density increases from the initial value of 3×10 3 cm −3 to the final value of 10 8 cm −3 , which matches the typical densities of hot corinos (see e.g. Woods et al 2013;Awad et al 2014;Coutens et al 2018). Visual extinction changes correspondingly from the starting value of A v =2, and gas and dust temperatures are assumed to be equal.…”

Section: Comparison With the Chemical Modelmentioning

confidence: 67%

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293–2422

Rivilla

Beltrán

Vasyunin

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The formyl radical HCO has been proposed as the basic precursor of many complex organic molecules such as methanol (CH 3 OH) or glycolaldehyde (CH 2 OHCHO). Using ALMA, we have mapped, for the first time at high angular resolution (∼1 ′′ , ∼140 au), HCO towards the Solar-type protostellar binary IRAS 16293−2422, where numerous complex organic molecules have been previously detected. We also detected several lines of the chemically related species H 2 CO, CH 3 OH and CH 2 OHCHO. The observations revealed compact HCO emission arising from the two protostars. The line profiles also show redshifted absorption produced by foreground material of the circumbinary envelope that is infalling towards the protostars. Additionally, IRAM 30m single-dish data revealed a more extended HCO component arising from the common circumbinary envelope. The comparison between the observed molecular abundances and our chemical model suggests that whereas the extended HCO from the envelope can be formed via gas-phase reactions during the cold collapse of the natal core, the HCO in the hot corinos surrounding the protostars is predominantly formed by the hydrogenation of CO on the surface of dust grains and subsequent thermal desorption during the protostellar phase. The derived abundance of HCO in the dust grains is high enough to produce efficiently more complex species such as H 2 CO, CH 3 OH, and CH 2 OHCHO by surface chemistry. We found that the main formation route of CH 2 OHCHO is the reaction between HCO and CH 2 OH.

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Section: Comparison With the Chemical Modelmentioning

confidence: 67%

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293–2422

Rivilla

Beltrán

Vasyunin

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…On the other hand, the D frac (NH 3 ) measured in our work (≥0.1) is larger than the values predicted on ices by Aikawa et al (2012), suggesting that the emission we see must include a contribution from material formed through gas-phase reactions. Awad et al (2014) modelled the deuterium chemistry of star-forming cores using both gas-phase and grain-surface reactions, but focus on the protostellar phase, when the evaporation of the icy mantles of dust grains is at its maximum. The model that best reproduces a HMPO predicts D frac (NH 3 ) ∼ 10 −3 −10 −2 and D frac (CH 3 OH) ≤ 4 × 10 −3 , both of which are smaller than our observed values.…”

Section: Deuterated Fraction Of Methanolmentioning

confidence: 99%

Deuteration and evolution in the massive star formation process

Fontani

Busquet

Palau

et al. 2015

A&A

131

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Context. An ever growing number of observational and theoretical evidence suggests that the deuterated fraction (column density ratio between a species containing D and its hydrogenated counterpart, D frac ) is an evolutionary indicator both in the low-and the highmass star formation process. However, the role of surface chemistry in these studies has not been quantified from an observational point of view. Aims. Because many abundant species, such as NH 3 , H 2 CO, and CH 3 OH, are actively produced on ice mantles of dust grains during the early cold phases, their D frac is expected to evolve differently from species formed only (or predominantly) in the gas, such as N 2 H + , HNC, HCN, and their deuterated isotopologues. The differences are expected to be relevant especially after the protostellar birth, in which the temperature rises, causing the evaporation of ice mantles. Methods. To compare how the deuterated fractions of species formed only in the gas and partially or uniquely on grain surfaces evolve with time, we observed rotational transitions of CH 3 OH, 13 CH 3 OH, CH 2 DOH, and CH 3 OD at 3 mm and 1.3 mm, of NH 2 D at 3 mm with the IRAM-30 m telescope, and the inversion transitions (1, 1) and (2, 2) of NH 3 with the GBT, towards most of the cores already observed in N 2 H + , N 2 D + , HNC, and DNC. Results. NH 2 D is detected in all but two cores, regardless of the evolutionary stage. D frac (NH 3 ) is on average above 0.1 and does not change significantly from the earliest to the most evolved phases, although the highest average value is found in the protostellar phase (∼0.3). Few lines of CH 2 DOH and CH 3 OD are clearly detected, and then only towards protostellar cores or externally heated starless cores. In quiescent starless cores, we have only one doubtful detection of CH 2 DOH. Conclusions. This work clearly confirms an expected different evolutionary trend of the species formed exclusively in the gas (N 2 D + and N 2 H + ) and those formed partially (NH 2 D and NH 3 ) or totally (CH 2 DOH and CH 3 OH) on grain mantles. It also reinforces the idea that D frac (N 2 H + ) is the best tracer of massive starless cores, while high values of D frac (CH 3 OH) seem fairly good tracers of the early protostellar phases, where the evaporation or sputtering of the grain mantles is most efficient.

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“…Overviews are available in, e.g., Albertsson et al (2013), Taquet, Charnley & Sipilä (2014), Awad et al (2014), and Ceccarelli et al (2014). Specific attention has been paid to deuterium fractionation of water by Taquet 2014), van Dishoeck, Herbst & Neufeld (2013), and Wakelam et al (2014).…”

Section: Deuterium Fractionation Rd or D/h = [Xd]/[xh] Represents Thementioning

confidence: 99%

“…The abundances and deuteration of some organic species become almost steady after the evaporation events, thanks to hightemperature ion-neutral reactions (e.g. Willacy & Woods 2009;Awad et al 2014). In our model, carbon chains are formed mainly in reactions on grain outer surfaces.…”

Section: Deuterium Fractionation Of Gaseous Speciesmentioning

confidence: 99%

Chemical fractionation of deuterium in the protosolar nebula

Kalvāns

Shmeld

Kalnin

et al. 2017

Mon. Not. R. Astron. Soc.

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Understanding gas-grain chemistry of deuterium in star-forming objects may help to explain their history and present state. We aim to clarify how processes in ices affect the deuterium fractionation. In this regard, we investigate a Solar-mass protostellar envelope using an astrochemical rate-equation model that considers bulk-ice chemistry. The results show a general agreement with the molecular D/H abundance ratios observed in low-mass protostars. The simultaneous processes of ice accumulation and rapid synthesis of HD on grain surfaces in the prestellar core hampers the deuteration of icy species. The observed very high D/H ratios exceeding 10 per cent, i.e., superdeuteration, are reproduced for formaldehyde and dimethyl ether, but not for other species in the protostellar envelope phase. Chemical transformations in bulk ice lower D/H ratios of icy species and do not help explaining the super-deuteration. In the protostellar phase, the D 2 O/HDO abundance ratio was calculated to be higher than the HDO/H 2 O ratio owing to gas-phase chemistry. Species that undergo evaporation from ices have high molecular D/H ratio and a high gas-phase abundance.

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Deuterium chemistry of dense gas in the vicinity of low-mass and massive star-forming regions

Cited by 17 publications

References 77 publications

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293–2422

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293–2422

Deuteration and evolution in the massive star formation process

Chemical fractionation of deuterium in the protosolar nebula

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