Mapping deuterated methanol toward L1544. I. Deuterium fraction and comparison with modeling
Abstract
Context. The study of deuteration in pre-stellar cores is important in order to understand the initial physical and chemical conditions in the process of star formation. In particular, observations toward pre-stellar cores of methanol and deuterated methanol, solely formed on the surface of dust grains, may provide useful insights into surface processes at low temperatures.
Aims: Here we analyze maps of CO, methanol, formaldehyde, and their deuterated isotopologues toward a well-known pre-stellar core. This study allows us to test current gas-dust chemical models.
Methods: Single-dish observations of CH3OH, CH2DOH, H2CO, H213 CO, HDCO, D2CO, and C17O toward the prototypical pre-stellar core L1544 were performed at the IRAM 30 m telescope. We analyze their column densities and distributions, and compare these observations with gas-grain chemical models.
Results: The maximum deuterium fraction derived for methanol is [CH2DOH]/[CH3OH] 0.08 ± 0.02, while the measured deuterium fractions of formaldehyde at the dust peak are [HDCO]/[H2CO] 0.03 ± 0.02, [D2CO]/[H2CO] 0.04 ± 0.03, and [D2CO]/[HDCO] 1.2 ± 0.3. Observations differ significantly from the predictions of models, finding discrepancies between a factor of 10 and a factor of 100 in most cases. It is clear though that to efficiently produce methanol on the surface of dust grains, quantum tunneling diffusion of H atoms must be switched on. It also appears that the currently adopted reactive desorption efficiency of methanol is overestimated and/or that abstraction reactions play an important role. More laboratory work is needed to shed light on the chemistry of methanol, an important precursor of complex organic molecules in space.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 2019
- DOI:
- 10.1051/0004-6361/201832703
- arXiv:
- arXiv:1808.09871
- Bibcode:
- 2019A&A...622A.141C
- Keywords:
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- astrochemistry;
- ISM: clouds;
- ISM: individual objects: L1544;
- stars: formation;
- ISM: molecules;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication in A&