Nascent chemical complexity in the prestellar core IRAS 16293E: Complex organics and deuterated methanol

Prestellar cores represent early sites of low-mass (M łeq few M_⊙) star and planet formation and provide insight into the initial chemical conditions of complex organic molecules (COMs). Deuterated COMs trace the degree of molecular inheritance and/or reprocessing, as high deuteration in protostellar systems suggests COMs forming during the prestellar stage when deuteration was enhanced. Within the L1689N molecular cloud, the prestellar core IRAS 16293E sits $90 eastward of the chemically rich IRAS 16293-2422 A and B protostellar system. A unique view of star formation inside a common natal cloud, IRAS,16293A, B, and E all show some of the highest levels of deuteration in the interstellar medium, with a number of D/H ratios 10^5 times higher than solar. We investigated the deuteration levels of the simplest COM, methanol (CH_3OH), in IRAS,16293E for the first time. Using the Arizona Radio Observatory (ARO) 12,m telescope, we targeted favorable transitions of CH_2DOH, CHD_2OH, ^13CH_3OH, and several higher-complexity COMs (including acetaldehyde, CH_3CHO, methyl formate, HCOOCH_3, and dimethyl ether, CH_3OCH_3) in the 3 mm band. Follow-up observations with the Yebes 40,m telescope provided additional transitions in the 7mm (Q band). We report the first detections of these COMs and deuterated methanol in the prestellar core IRAS,16293E and used our observations to calculate excitation temperatures, column densities, and relative abundance ratios. Striking similarities were found between relative molecular ratios and D/H values when we compared IRAS 16293E to the A and B protostars in addition to to a heterogeneous sample of other prestellar cores, protostars, and comet 67P/Churyumov-Gerasimenko. Our results support the idea that there is a limited amount of chemical reprocessing of COMs when prestellar cores collapse and heat up during the protostellar phase.