The ALMA-PILS survey: First detections of ethylene oxide, acetone and propanal toward the low-mass protostar IRAS 16293-2422
Journal article, 2017

Context. One of the open questions in astrochemistry is how complex organic and prebiotic molecules are formed. The unsurpassed sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) takes the quest for discovering molecules in the warm and dense gas surrounding young stars to the next level. Aims. Our aim is to start the process of compiling an inventory of oxygen-bearing complex organic molecules toward the solar-type Class 0 protostellar binary IRAS 16293-2422 from an unbiased spectral survey with ALMA, Protostellar Interferometric Line Survey (PILS). Here we focus on the new detections of ethylene oxide (c-C2H4O), acetone (CH3COCH3), and propanal (C2H5CHO). Methods. With ALMA, we surveyed the spectral range from 329 to 363 GHz at 0.5? (60 AU diameter) resolution. Using a simple model for the molecular emission in local thermodynamical equilibrium, the excitation temperatures and column densities of each species were constrained. Results. We successfully detect propanal (44 lines), ethylene oxide (20 lines) and acetone (186 lines) toward one component of the protostellar binary, IRAS 16293B. The high resolution maps demonstrate that the emission for all investigated species originates from the compact central region close to the protostar. This, along with a derived common excitation temperature of Tex ? 125 K, is consistent with a coexistence of these molecules in the same gas. Conclusions. The observations mark the first detections of acetone, propanal and ethylene oxide toward a low-mass protostar. The relative abundance ratios of the two sets of isomers, a CH3COCH3/C2H5CHO ratio of 8 and a CH3CHO/c-C2H4O ratio of 12, are comparable to previous observations toward high-mass protostars. The majority of observed abundance ratios from these results as well as those measured toward high-mass protostars are up to an order of magnitude above the predictions from chemical models. This may reflect either missing reactions or uncertain rates in the chemical networks. The physical conditions, such as temperatures or densities, used in the models, may not be applicable to solar-type protostars either.

ISM: Individual object: IRAS 16293-2422 line: Identification

Astrobiology

Astrochemistry

ISM: Molecules

ISM: Abundances

Author

J. M. Lykke

Kobenhavns Universitet

A. Coutens

University College London (UCL)

J. K. Jorgensen

Kobenhavns Universitet

M. H. D. van der Wiel

Kobenhavns Universitet

R. T. Garrod

University of Virginia

H. S. P. Müller

University of Cologne

Per Bjerkeli

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

T. L. Bourke

SKA Organization

H. Calcutt

Kobenhavns Universitet

M. N. Drozdovskaya

Leiden University

C. Favre

Université Grenoble Alpes

CNRS Centre National de la Recherche Scientifique

E. C. Fayolle

Harvard-Smithsonian Center for Astrophysics

S. K. Jacobsen

Kobenhavns Universitet

K. I. Öberg

Harvard-Smithsonian Center for Astrophysics

M. V. Persson

Leiden University

E. F. van Dishoeck

Leiden University

Max Planck Institute

S. F. Wampfler

University of Bern

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 597 A53-

Driving Forces

Sustainable development

Infrastructure

Onsala Space Observatory

Subject Categories

Other Chemical Engineering

DOI

10.1051/0004-6361/201629180