Deuterium fractionation in warm dense interstellar clumps

Roueff, E.; Parise, B.; Herbst, Eric

doi:10.1051/0004-6361:20066531

Cited by 65 publications

(76 citation statements)

References 31 publications

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“…Pure gas-phase chemistry can lead to elevated deuterium fractionations for H 2 CO. We have here adopted the low-metalicity (or depleted) model of Roueff et al (2007) as their warm-core (and un-depleted) model shows low deuterium fractionations. The steady-state model work presented here includes the updates and modifications of Parise et al (2009), and we have used it to predict relevant D/H ratios for H 2 CO and N 2 H + .…”

Section: Gas-phase Chemistry Modelsmentioning

confidence: 99%

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Deuterated formaldehyde inρOphiuchi A

Bergman

Parise

Liseau

et al. 2011

A&A

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Context. Formaldehyde is an organic molecule that is abundant in the interstellar medium. High deuterium fractionation is a common feature in low-mass star-forming regions. Observing several isotopologues of molecules is an excellent tool for understanding the formation paths of the molecules. Aims. We seek an understanding of how the various deuterated isotopologues of formaldehyde are formed in the dense regions of lowmass star formation. More specifically, we adress the question of how the very high deuteration levels (several orders of magnitude above the cosmic D/H ratio) can occur using H 2 CO data of the nearby ρ Oph A molecular cloud. Methods. From mapping observations of H 2 CO, HDCO, and D 2 CO, we have determined how the degree of deuterium fractionation changes over the central 3 × 3 region of ρ Oph A. The multi-transition data of the various H 2 CO isotopologues, as well as from other molecules (e.g., CH 3 OH and N 2 D + ) present in the observed bands, were analysed using both the standard type rotation diagram analysis and, in selected cases, a more elaborate method of solving the radiative transfer for optically thick emission. In addition to molecular column densities, the analysis also estimates the kinetic temperature and H 2 density. Results. Toward the SM1 core in ρ Oph A, the H 2 CO deuterium fractionation is very high. In fact, the observed D 2 CO/HDCO ratio is 1.34 ± 0.19, while the HDCO/H 2 CO ratio is 0.107 ± 0.015. This is the first time, to our knowledge, that the D 2 CO/HDCO abundance ratio is observed to be greater than 1. The kinetic temperature is in the range 20−30 K in the cores of ρ Oph A, and the H 2 density is (6−10) × 10 5 cm −3 . We estimate that the total H 2 column density toward the deuterium peak is (1−4) × 10 23 cm −2 . As depleted gas-phase chemistry is not adequate, we suggest that grain chemistry, possibly due to abstraction and exchange reactions along the reaction chain H 2 CO → HDCO → D 2 CO, is at work to produce the very high deuterium levels observed.

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Section: Gas-phase Chemistry Modelsmentioning

confidence: 99%

“…11. Gas-phase steady-state models based on the reaction network by Roueff et al (2007). Shown are the D/H predicted ratios; HDCO/H 2 CO (top), D 2 CO/HDCO (middle), and N 2 D + /N 2 H + (bottom) as function of temperature and for two different H 2 densities (5 × 10 5 cm −3 and 1 × 10 6 cm −3 ).…”

Section: Grain Chemistry Modelsmentioning

confidence: 99%

Deuterated formaldehyde inρOphiuchi A

Bergman

Parise

Liseau

et al. 2011

A&A

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“…The route involving H + 3 is the dominant one at very low temperatures (T < 20 K), whereas the importance of CH + 3 takes over at slightly higher temperatures (20 < T < 40 K) owing to its higher endothermicity (Turner 2001;Roueff et al 2007;Parise et al 2009). H 2 D + is thus a very good probe of very cold objects, and has been extensively used in recent years Based on observations with the APEX telescope.…”

Section: Introductionmentioning

confidence: 99%

Extended emission of D₂H⁺in a prestellar core

Parise

Беллоче

et al. 2010

A&A

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Context. In the past years, the H 2 D + and D 2 H + molecules have gained attention as probes of cold and depleted dense molecular cloud cores. These ions are the basis of molecular deuterium fractionation, a common characteristic observed in star-forming regions. H 2 D + is now routinely observed, but the search for its isotopologue D 2 H + is still difficult because of the high frequency of its ground para transition (692 GHz). Aims. We observed molecular transitions of H 2 D + and D 2 H + in a cold prestellar core to characterize the roots of deuterium chemistry. Methods. Thanks to the sensitive multi-pixel CHAMP + receiver on the APEX telescope where the required excellent weather conditions are met, we not only successfully detect D 2 H + in the H-MM1 prestellar core located in the L1688 cloud, but also obtain information on the spatial extent of its emission. We also detect H 2 D + at 372 GHz in the same source. We analyze these detections using a non-LTE radiative transfer code and a state-of-the-art spin-dependent chemical model.Results. This observation is the first secure detection of D 2 H + in space. The emission is moreover extended over several pixels of the CHAMP + array, i.e. on a scale of at least 40 , corresponding to ∼4800 AU. We derive column densities on the order of 10 12 -10 13 cm −2 for both molecules in the LTE approximation depending on the assumed temperature, and up to two orders of magnitude higher based on a non-LTE analysis. Conclusions. Our modeling suggests that the level of CO depletion must be extremely high (>10, and even >100 if the temperature of the core is around 10 K) at the core center, contradicting CO depletion levels directly measured in other cores. Observation of the H 2 D + spatial distribution and direct measurement of the CO depletion in H-MM1 will be essential to confirm whether present chemical models investigating the basis of deuterium fractionation of molecules need to be revised.

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“…In high excitation ammonia studies, SMA1 and SMA2 dominate the emission; emission was not detected toward SMA3 and SMA4. Column densities on the order of N T ot = 2 × 10 14 are indicated for T rot ∼50 K. The study of deuterium fractionation in warm clumps recently published by Roueff, Parise and Herbst (2007) …”

Section: Introductionmentioning

confidence: 90%

A Search for Interstellar CH₂D⁺

Wootten¹,

Turner²

2008

Proc. IAU

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Abstract. We report on a search for interstellar CH2 D + . Four transitions occur in easily accessible portions of the spectrum; we report on emission at the frequencies of these transitions toward high column density star-forming regions. While the observations can be interpreted as being consistent with a detection of the molecule, further observations will be needed to secure its identification. The CH 2 D + rotational spectrum has not been measured to high accuracy. Its lines are weak, as the dipole moment induced by the inclusion of deuterium in the molecule is small. Astronomical detection is favored by observations toward strongly deuterium-fractionated sources. However, enhanced deuteration is expected to be most significant at low temperatures. The sparseness of the available spectrum and the low excitation in regions of high fractionation make secure identification of CH 2 D + difficult. Nonetheless, owing to the importance of CH + 3 to interstellar chemistry, and the lack of rotational transitions of that molecule owing to its planar symmetric structure, a measure of its abundance would provide key data to astrochemical models.

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Deuterium fractionation in warm dense interstellar clumps

Cited by 65 publications

References 31 publications

Deuterated formaldehyde inρOphiuchi A

Deuterated formaldehyde inρOphiuchi A

Extended emission of D₂H⁺in a prestellar core

A Search for Interstellar CH₂D⁺

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Deuterium fractionation in warm dense interstellar clumps

Cited by 65 publications

References 31 publications

Deuterated formaldehyde inρOphiuchi A

Deuterated formaldehyde inρOphiuchi A

Extended emission of D2H+in a prestellar core

A Search for Interstellar CH2D+

Contact Info

Product

Resources

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Extended emission of D₂H⁺in a prestellar core

A Search for Interstellar CH₂D⁺