First Detection of CH3OD in Prestellar Cores

TL;DR

This study reports the first detection of CH3OD in prestellar cores, providing new data on isotopic ratios that inform our understanding of chemical processes during star formation.

Contribution

It presents the first measurements of CH3OD and related isotopic ratios in prestellar cores, filling a critical data gap and testing existing assumptions about chemical inheritance.

Findings

Detected CH3OD in two prestellar cores, L1448 and B213-C6.

Measured CH2DOH/CH3OD ratios between 2.8 and 8.5, consistent with statistical expectations.

Derived D/H ratios for both isotopologues, indicating chemical processing in prestellar stages.

Abstract

The isotopic ratios of deuterated methanol derived around protostars are commonly used to infer the physical conditions under which they formed in the earlier prestellar stage. However, there is a discrepancy in the ratio of the singly deuterated methanol isotopologues, CH2DOH/CH3OD, between low- and high-mass protostars, which puts into question whether prestellar isotopic ratios are generally preserved during the star- and planet-forming process. Resolving this puzzle is only made harder by the complete lack of data on this ratio in the prestellar stage. This work presents observations with the IRAM 30m telescope that securely detect CH3OD in the prestellar core L1448 in Perseus and tentatively in B213-C6 in Taurus. This work constrains the ratio of CH2DOH/CH3OD and the D/H ratios for both singly deuterated methanol isotopologues for the first time at the prestellar stage. Column densities calculated under the assumption of local thermal equilibrium lead to a CH2DOH/CH3OD ratio of 2.8-8.5 in L1448 and $\leq$ 5.7 in B213-C6. The values are marginally consistent with the statistically expected ratio of 3, but most assumptions put the values in an elevated range in line with values found around low-mass protostars. The D/H ratio in CH2DOH is between 3.6% and 6.8% in L1448 and in the range of 2.4-5.8% in B213-C6. The D/H ratio derived for CH3OD is lower, namely 1.4-4.4% in L1448 and $\leq$ 3.8% in B213-C6.