13C-METHYL FORMATE IN ORION-KL: ALMA OBSERVATIONS AND SPECTROSCOPIC CHARACTERIZATION

Cécile Favre,Suzanne Bisschop,Nathalie Brouillet,Didier Despois,L Margulès,Nathan Crockett,Isabelle Kleiner,Edwin Bergin,Alain Baudry,Justin Neill,T Huet,Jes Jørgensen,Jean Demaison,Miguel Carvajal,David Field

doi:10.15278/isms.2014.tf06

Abstract

Determination of elemental isotopic ratios is valuable for understanding the chemical evolution of interstellar material. Until now the 12C/13C ratio has predominantly been measured in simple species such as CO, CN and H2CO and, becomes larger with increasing distance from the Galactic Center. We have investigated the carbon isotopic ratio for methyl formate HCOOCH3, and its isotopologues H13COOCH3 and HCOO13CH3 addressing the issue whether the 12C/13C ratio is the same for both simple and large molecules. Using ALMA science verification observations of Orion-KL and the spectroscopic characterization of the complex H13COOCH3 and HCOO13CH3 species that we have performed, we have 1) confirmed the detection of the 13C-methyl formate species in Orion-KL and, 2) image for the first time their spatial distribution. I will present some of these results. In particular, our analysis shows that the 12C/13C isotope ratio in methyl formate toward the Compact Ridge and Hot Core-SW components that are associated with Orion-KL are, for both the 13C-methyl formate isotopologues, commensurate with the well-known 12C/13C ratio of the simple species CO. Our findings suggest that grain surface chemistry very likely prevails in the formation of methyl formate main and 13C isotopologues.

Highlights

12C/13C ratio can be used to distinguish a gas-phase origin from an ice mantle one for complex molecules v The case of CH3OH (Wirström et al 2011)
- Input parameters (Θ, Tr, N, vLSR and ∆vLSR), the values derived by our previous PdBI observations, which were performed with a similar angular resolution the ALMA-SV data
MF column densities differ by a factor 3.8±1.7 toward the Hot Core-SW (HC-SW) and 2.4±0.7 toward the Compact Ridge (CR) between PdBI and ALMA data (Carvajal, Kleiner et al in prep.)

Summary

Introduction

12C/13C ratio can be used to distinguish a gas-phase origin from an ice mantle one for complex molecules v The case of CH3OH (Wirström et al 2011) If formed on dust grains from hydrogenation of CO (Cuppen et al 2009): 12C/13C ratio in CH3OH and CO should be similar V Investigation to HCOOCH3 (Favre, Carvajal et al sub.) HCOOCH3 may be efficiently formed close to the surface in icy grain mantles during the hot core warm up phase (CR induced photodissociation of CH3OH ices)

Results

Conclusion