O-bearing complex organic molecules at the cyanopolyyne peak of TMC-1: detection of CHCHO, CHOH, HCOOCH, and CHOCH.

We report the detection of the oxygen-bearing complex organic molecules propenal (CHCHO), vinyl alcohol (CHOH), methyl formate (HCOOCH), and dimethyl ether (CHOCH) toward the cyanopolyyne peak of the starless core TMC-1. These molecules are detected through several emission lines in a deep Q-band line survey of TMC-1 carried out with the Yebes 40m telescope. These observations reveal that the cyanopolyyne peak of TMC-1, which is the prototype of cold dark cloud rich in carbon chains, contains also O-bearing complex organic molecules like HCOOCH and CHOCH, which have been previously seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of CHOH in space and the first time that CHCHO and CHOH are detected in a cold environment, adding new pieces in the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2 ± 0.3) × 10 cm, (2.5 ± 0.5) × 10 cm, (1.1 ± 0.2) × 10 cm, and (2.5 ± 0.7) × 10 cm for CHCHO, CHOH, HCOOCH, and CHOCH, respectively. Interestingly, CHOH has an abundance similar to that of its well known isomer acetaldehyde (CHCHO), with CHOH/CHCHO ~ 1 at the cyanopolyyne peak. We discuss potential formation routes to these molecules and recognize that further experimental, theoretical, and astronomical studies are needed to elucidate the true mechanism of formation of these O-bearing complex organic molecules in cold interstellar sources.