Letter to the Editor

O-bearing complex organic molecules at the cyanopolyyne peak of TMC-1: Detection of C₂H₃CHO, C₂H₃OH, HCOOCH₃, and CH₃OCH₃^⋆

¹ Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
e-mail: marcelino.agundez@csic.es
² Observatorio Astronómico Nacional, IGN, Calle Alfonso XII 3, 28014 Madrid, Spain
³ Observatorio de Yebes, IGN, Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain

Received: 1 April 2021
Accepted: 21 April 2021

Abstract

We report the detection of the oxygen-bearing complex organic molecules propenal (C₂H₃CHO), vinyl alcohol (C₂H₃OH), methyl formate (HCOOCH₃), and dimethyl ether (CH₃OCH₃) toward the cyanopolyyne peak of the starless core TMC-1. These molecules were 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 a prototype of a cold dark cloud rich in carbon chains, also contains O-bearing complex organic molecules such as HCOOCH₃ and CH₃OCH₃, which have previously been seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C₂H₃OH in space and the first time that C₂H₃CHO and C₂H₃OH have been detected in a cold environment, adding new pieces to the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2 ± 0.3) × 10¹¹ cm⁻², (2.5 ± 0.5) × 10¹² cm⁻², (1.1 ± 0.2) × 10¹² cm⁻², and (2.5 ± 0.7) × 10¹² cm⁻² for C₂H₃CHO, C₂H₃OH, HCOOCH₃, and CH₃OCH₃, respectively. Interestingly, C₂H₃OH has an abundance similar to that of its well-known isomer acetaldehyde (CH₃CHO), with C₂H₃OH/CH₃CHO ∼ 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 formation mechanism of these O-bearing complex organic molecules in cold interstellar sources.