Depletion of chlorine into HCI ice in a protostellar core: The CHESS spectral survey of OMC-2 FIR 4

The freeze-out of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freeze-out of various carriers of elements with abundances < 10-5 has not yet...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2015-02, Vol.574
Main Authors: Kama, M, Caux, E, Lopez-Sepulcre, A, Wakelam, V, Dominik, C, Ceccarelli, C, Lanza, M, Lique, F, Ochsendorf, B B, Lis, D C, Caballero, R N, Tielens, A G G M
Format: Article
Language:English
Subjects:
Carbon monoxide
Chlorine
Clouds
Depletion
Grains
Icebergs
Mathematical models
Protostars
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Summary:The freeze-out of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freeze-out of various carriers of elements with abundances < 10-5 has not yet been well studied. We observed transitions of HCl and H[sub 2]Cl[sup +] towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Sub-millimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated Hcl-H[sub 2] hyperfine collisional excitation rate coefficients. Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201424737