ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars

Motivation, sample, calibration, and initial results

¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
² Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: Leen.Decin@kuleuven.be
³ University of Leeds, School of Chemistry, Leeds LS2 9JT, UK
⁴ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
⁵ University College London, Department of Physics and Astronomy, London WC1E 6BT, UK
⁶ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
⁷ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁸ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
⁹ Open University, Walton Hall, Milton Keynes MK7 6AA, UK
¹⁰ Université de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, 33615 Pessac, France
¹¹ Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
¹² University of Amsterdam, Anton Pannekoek Institute for Astronomy, 1090 GE Amsterdam, The Netherlands
¹³ KU Leuven, Center for mathematical Plasma Astrophysics, 3001 Leuven, Belgium
¹⁴ National Astronomical Research Institute of Thailand, Chiangmai 50180, Thailand
¹⁵ Max-Planck-Institut für Radioastronomie, 53121 Bonn, Germany
¹⁶ Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique, Observatoire de Paris, Université Paris Sciences et Lettres, Centre National de la Recherche Scientifique, Sorbonne Université, Université de Paris, 92195 Meudon, France
¹⁷ Université Côte d’Azur, Laboratoire Lagrange, Observatoire de la Côte d’Azur, 06304 Nice Cedex 4, France
¹⁸ Universität zu Köln, I. Physikalisches Institut, 50937 Köln, Germany
¹⁹ California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA 91109, USA
²⁰ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²¹ SRON Netherlands Institute for Space Research, 3584 CA Utrecht, The Netherlands
²² Radboud University, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Nijmegen, The Netherlands
²³ University of Hong Kong, Laboratory for Space Research, Pokfulam, Hong Kong

Received: 27 January 2021
Accepted: 17 November 2021

Abstract

This overview paper presents ATOMIUM, a Large Programme in Cycle 6 with the Atacama Large Millimeter/submillimeter Array (ALMA). The goal of ATOMIUM is to understand the dynamics and the gas phase and dust formation chemistry in the winds of evolved asymptotic giant branch (AGB) and red supergiant (RSG) stars. A more general aim is to identify chemical processes applicable to other astrophysical environments. Seventeen oxygen-rich AGB and RSG stars spanning a range in (circum)stellar parameters and evolutionary phases were observed in a homogeneous observing strategy allowing for an unambiguous comparison. Data were obtained between 213.83 and 269.71 GHz at high (∼0″​​.025–0″​​.050), medium (∼0″​​.13–0″​​.24), and low (∼1″) angular resolution. The sensitivity per ∼1.3 km s⁻¹ channel was 1.5–5 mJy beam⁻¹, and the line-free channels were used to image the millimetre wave continuum. Our primary molecules for studying the gas dynamics and dust formation are CO, SiO, AlO, AlOH, TiO, TiO₂, and HCN; secondary molecules include SO, SO₂, SiS, CS, H₂O, and NaCl. The scientific motivation, survey design, sample properties, data reduction, and an overview of the data products are described. In addition, we highlight one scientific result – the wind kinematics of the ATOMIUM sources. Our analysis suggests that the ATOMIUM sources often have a slow wind acceleration, and a fraction of the gas reaches a velocity which can be up to a factor of two times larger than previously reported terminal velocities assuming isotropic expansion. Moreover, the wind kinematic profiles establish that the radial velocity described by the momentum equation for a spherical wind structure cannot capture the complexity of the velocity field. In fifteen sources, some molecular transitions other than ¹²CO v = 0 J = 2 − 1 reach a higher outflow velocity, with a spatial emission zone that is often greater than 30 stellar radii, but much less than the extent of CO. We propose that a binary interaction with a (sub)stellar companion may (partly) explain the non-monotonic behaviour of the projected velocity field. The ATOMIUM data hence provide a crucial benchmark for the wind dynamics of evolved stars in single and binary star models.