Abstract
We investigate the deuteration of methanol towards the high-mass star-forming region NGC 7538-IRS1. We carried out a multi-transition study of CH3OH, 13CH3OH, and the deuterated flavors, CH2DOH and CH3OD, between 1.0 and 1.4 mm with the IRAM-30 m antenna. In total, 34 13CH3OH, 13 CH2DOH lines and 20 CH3OD lines spanning a wide range of upper-state energies (Eup) were detected. From the detected transitions, we estimate that the measured D/H does not exceed 1%, with a measured CH2DOH/CH3OH and CH3OD/CH3OH of about (32 ± 8) × 10−4 and (10 ± 4) × 10−4, respectively. This finding is consistent with the hypothesis of a short-timescale formation during the pre-stellar phase. We find a relative abundance CH2DOH/CH3OD ratio of 3.2 ± 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.
Highlights
Observational studies of deuterated molecules are powerful ways to probe the chemical and physical evolution of star-forming regions
A&A 627, A80 (2019) In this study, we investigate the D/H ratio for methanol (CH3OH, CH2DOH, and CH3OD) towards the high-mass starforming region NGC 7538-IRS1 (L = 1.3 × 105 L, d = 2.8 kpc, M ∼ 30 M, see Bisschop et al 2007; Beuther et al 2012), which is known to harbor high abundances of organic molecules, including methanol (e.g., Bisschop et al 2007; Wirström et al 2011)
We detect several bright lines covering a wide range of upper energy levels: 34 13CH3OH lines with Eup spanning from 23 to 397 K; 13 CH2DOH lines with Eup spanning from 25 to
Summary
Observational studies of deuterated molecules are powerful ways to probe the chemical and physical evolution of star-forming regions. The difference in zero-point energy between deuterated molecules and their hydrogenated counterparts (about 1000 K for methanol and its singly deuterated flavors, Nandi et al 2019) makes it possible for deuterated species to be formed with significantly higher relative abundances than the elemental D/H ratio (∼10−5, see e.g., Ceccarelli et al 2007, 2014; Caselli & Ceccarelli 2012). These enhanced abundance ratios can be preserved as the protostar heats the gas to temperatures large enough (≥100 K) to evaporate the ice mantles.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
