Deuterated methanol toward NGC 7538-IRS1

Abstract

We investigate the deuteration of methanol towards the high-mass star forming region NGC 7538-IRS1. We have carried out a multi-transition study of CH${}_3$OH, ${}^{13}$CH${}_3$OH and of the deuterated fllavors, CH${}_2$DOH and CH${}_3$OD, between 1.0--1.4 mm with the IRAM-30~m antenna. In total, 34 ${}^{13}$CH${}_3$OH, 13 CH${}_2$DOH lines and 20 CH${}_3$OD lines spanning a wide range of upper-state energies (E${}_{up}$) were detected. From the detected transitions, we estimate that the measured D/H does not exceed 1$\%$, with a measured CH${}_2$DOH/CH${}_3$OH and CH${}_3$OD/CH${}_3$OH of about (32$\pm$8)$\times$10${}^{-4}$ and (10$\pm$4)$\times$10${}^{-4}$, respectively. This finding is consistent with the hypothesis of a short-time scale formation during the pre-stellar phase. We find a relative abundance ratio CH${}_2$DOH/CH${}_3$OD of 3.2 $\pm$ 1.5. This result is consistent with a statistical deuteration. We cannot exclude H/D exchanges between water and methanol if water deuteration is of the order 0.1$\%$, as suggested by recent Herschel observations.

arXiv commentAccepted for publication in Astronomy & Astrophysics

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