Volume 528, April 2011
|Number of page(s)||5|
|Published online||01 March 2011|
Letters to the Editor
The puzzling deuteration of methanol in low- to high-mass protostars⋆
UJF-Grenoble 1/CNRS, Institut de Planétologie et d’Astrophysique de
Grenoble (IPAG) UMR 5274,
Accepted: 16 February 2011
Context. The current theory of methanol deuteration on interstellar grains predicts that the abundance ratio of the singly deuterated isotopologues [CH2DOH]/[CH3OD] should always be ~3. In warm regions where grain mantles have sublimated, gaseous methanol is detectable via its rotational transitions. In previous observational studies, the gas-phase [CH2DOH]/[CH3OD] ratio was measured and found to be significantly larger than 3 in low-mass protostars and close to 1 in the Orion IRc2 massive hot core.
Aims. We present new measurements of the gas-phase [CH2DOH]/[CH3OD] ratio in two additional high-mass protostars, as well as in two intermediate-mass protostars, to either confirm or exclude the dependence of this ratio on the mass of the protostar.
Methods. The observations were carried out using the IRAM-30 m telescope. Several rotational lines of each isotopologue were detected toward the intermediate-mass protostars, while only CH3OD lines were detected in the massive hot cores. The ratio [CH2DOH]/[CH3OD] (or its upper limit) was computed from both the averaged column densities and directly from line flux ratios.
Results. Our results confirm that the [CH2DOH]/[CH3OD] ratio is substantially lower in massive hot cores than in (low-mass) hot-corinos, by typically one order of magnitude. Furthermore, they suggest that intermediate-mass protostars have similar properties to low-mass protostars.
Conclusions. The measured [CH2DOH]/[CH3OD] ratios are inconsistent with the current theory of methanol deuteration, independently of the mass of the source. While the large ratios measured in low- and intermediate-mass sources can be explained qualitatively by various selective depletion mechanisms, the small ratios (<2) measured toward massive hot cores are puzzling. A revision of the deuterium chemistry in hot cores is suggested.
Key words: molecular processes / stars: protostars / ISM: molecules
Table A.1 is only available in electronic form at http://www.aanda.org
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.