Letter to the Editor

The ALMA-PILS survey: First tentative detection of 3-hydroxypropenal (HOCHCHCHO) in the interstellar medium and chemical modeling of the C₃H₄O₂ isomers

¹ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, UPS, CNRS, CNES, 9 av. du Colonel Roche, 31028 Toulouse Cedex 4, France
e-mail: audrey.coutens@irap.omp.eu
² Institut des Sciences Moléculaires (ISM), CNRS, Université Bordeaux, 351 cours de la Libération, 33400 Talence, France
³ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str.77, 50937 Köln, Germany
⁴ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁵ Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA), Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁶ Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark

Received: 4 January 2022
Accepted: 21 March 2022

Abstract

Characterizing the molecular composition of solar-type protostars is useful for improving our understanding of the physico-chemical conditions under which the Sun and its planets formed. In this work, we analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) data of the Protostellar Interferometric Line Survey (PILS), an unbiased spectral survey of the solar-type protostar IRAS 16293–2422, and we tentatively detected 3-hydroxypropenal (HOCHCHCHO) for the first time in the interstellar medium towards source B. Based on the observed line intensities and assuming local thermodynamic equilibrium, its column density is constrained to be ∼10¹⁵ cm⁻², corresponding to an abundance of 10⁻⁴ relative to methanol, CH₃OH. Additional spectroscopic studies are needed to constrain the excitation temperature of this molecule. We included HOCHCHCHO and five of its isomers in the chemical network presented in Manigand et al. (2021, A&A, 645, A53) and we predicted their chemical evolution with the Nautilus code. The model reproduces the abundance of HOCHCHCHO within the uncertainties. This species is mainly formed through the grain surface reaction CH₂CHO + HCO → HCOCH₂CHO, followed by the tautomerization of HCOCH₂CHO into HOCHCHCHO. Two isomers, CH₃COCHO and CH₂COHCHO, are predicted to be even more abundant than HOCHCHCHO. Spectroscopic studies of these molecules are essential in searching for them in IRAS 16293–2422 and other astrophysical sources.