Upper limit for the D<sub>2</sub>H<sup>+</sup>ortho-to-para ratio in the prestellar core 16293E (CHESS)

Vastel, C.; Caselli, P.; Ceccarelli, C.; Bacmann, A.; Lis, D. C.; Caux, E.; Codella, C.; Beckwith, James; Ridley, T.

doi:10.1051/0004-6361/201219616

Cited by 15 publications

(21 citation statements)

References 45 publications

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“…3). Finally we note that the ortho/para ratios predicted by our models at t = 10 6 years are for the most part compatible with recent modeling results of Vastel et al (2012; their complete depletion case), although our chemical network is much larger and the present model includes a time-dependent treatment of depletion.…”

Section: Ortho/para Ratiossupporting

confidence: 89%

HD depletion in starless cores

Sipilä

Caselli

Harju

2013

A&A

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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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Section: Ortho/para Ratiossupporting

confidence: 89%

HD depletion in starless cores

Sipilä

Caselli

Harju

2013

A&A

Self Cite

102

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“…Assuming a line-of-sight source size of 9.5 or 1140 au, equal to the geometric mean of the FWHM sizes in the plane of the sky, we derive an H 2 volume density of (1.1 − 1.9) × 10 7 cm −3 , depending on the dust temperature. This is an order of magnitude higher than the values derived in earlier single-dish studies (Stark et al 2004;Vastel et al 2012), but consistent with the best-model value of 1.4 × 10 7 cm −2 in the recent study of Bacmann et al (2016). The high central density in the model of Bacmann et al (2016) is in fact directly related to the presence of a temperature gradient.…”

Section: Properties Of the Dust Continuum Sourcesupporting

confidence: 88%

Star Formation and Feedback: A Molecular Outflow–prestellar Core Interaction in L1689n

Lis

Wootten

Gérin

et al. 2016

ApJ

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We present Herschel 1 , ALMA Compact Array (ACA), and Caltech Submillimeter Observatory (CSO) observations of the prestellar core in L1689N, which has been suggested to be interacting with a molecular outflow driven by the nearby solar type protostar IRAS 16293-2422. This source is characterized by some of the highest deuteration levels seen in the interstellar medium. The change in the NH 2 D line velocity and width across the core provides clear evidence of an interaction with the outflow, traced by the high-velocity water emission. Quiescent, cold gas, characterized by narrow line widths is seen in the NE part of the core, while broader, more disturbed line profiles are seen in the W/SW part. Strong N 2 D + and ND 3 emission is detected with the ACA, extending S/SW from the peak of the single-dish NH 2 D emission. The ACA data also reveal the presence a compact dust continuum source, with a mean size of ∼1100 au, a central density of (1 − 2) × 10 7 cm −3 , and a mass of 0.2-0.4 M . The dust emission peak is displaced ∼5 to the south with respect to the N 2 D + and ND 3 emission, as well as the single-dish dust continuum peak, suggesting that the northern, quiescent part of the core is characterized by spatially extended continuum emission, which is resolved out by the interferometer. We see no clear evidence of fragmentation in this quiescent part of the core, which could lead to a second generation of star formation, although a weak dust continuum source is detected in this region in the ACA data.

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“…This is reminiscent of the velocity differences seen in this source, where the velocity of the emission from deuteriumbearing species Stark et al 2004) are at the cloud velocity of 3.8−4 km s −1 (see the discussion in Vastel et al (2012), where more details on these various points can be found). The line widths found by fitting the HRS spectra are 0.4±0.02 km s −1 for both ND and NH, consistent with line widths measured in this source in other hydrides like ND 2 H .…”

Section: Resultsmentioning

confidence: 70%

Stratified NH and ND emission in the prestellar core 16293E in L1689N

Bacmann

Daniel

Caselli

et al. 2016

A&A

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Context. High degrees of deuterium fractionation are commonly found in cold prestellar cores and in the envelopes around young protostars. As it brings strong constraints to chemical models, deuterium chemistry is often used to infer core history or molecule formation pathways. Whereas a large number of observations are available regarding interstellar deuterated stable molecules, relatively little is known about the deuteration of hydride radicals, as their fundamental rotational transitions are at high frequencies where the atmosphere is mostly opaque. Aims. Nitrogen hydride radicals are important species in nitrogen chemistry, as they are thought to be related to ammonia formation. Methods. We observed NH and ND in 16293E with the HIFI spectrometer on board the Herschel Space Observatory as part of the CHESS guaranteed time key programme, and derived the abundances of these two species using a non local thermodynamic equilibrium radiative transfer model. Results. Both NH and ND are detected in the source, with ND in emission and NH in absorption against the continuum that arises from the cold dust emission. Our model shows, however, that the ND emission and the NH absorption originate from different layers in the cloud, as further evidenced by their different velocities. In the central region of the core, we can set a lower limit to the [ND]/[NH] ratio of > ∼ 2%. This estimate is consistent with recent pure gas-phase models of nitrogen chemistry.

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Upper limit for the D₂H⁺ortho-to-para ratio in the prestellar core 16293E (CHESS)

Cited by 15 publications

References 45 publications

HD depletion in starless cores

HD depletion in starless cores

Star Formation and Feedback: A Molecular Outflow–prestellar Core Interaction in L1689n

Stratified NH and ND emission in the prestellar core 16293E in L1689N

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Upper limit for the D2H+ortho-to-para ratio in the prestellar core 16293E (CHESS)

Cited by 15 publications

References 45 publications

HD depletion in starless cores

HD depletion in starless cores

Star Formation and Feedback: A Molecular Outflow–prestellar Core Interaction in L1689n

Stratified NH and ND emission in the prestellar core 16293E in L1689N

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Upper limit for the D₂H⁺ortho-to-para ratio in the prestellar core 16293E (CHESS)