ATOMIUM: halide molecules around the S-type AGB star W Aquilae
Journal article, 2021

Context. S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. W Aql is a nearby S-type star, with well-known circumstellar parameters, making it an ideal object for in-depth study of less common molecules. Aims. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. Methods. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of (AlCl)-Cl-35, (AlCl)-Cl-37, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. Results. AlCl is found in clumps very close to the star, with emission confined within 0 ''.1 of the star. AlF emission is more extended, with faint emission extending 0 ''.2 to 0 ''.6 from the continuum peak. We find peak abundances, relative to H-2, of 1.7 x 10(-7) for (AlCl)-Cl-35, 7 x 10(-8) for (AlCl)-Cl-37, and 1 x 10(-7) for AlF. From the PACS spectra, we find abundances of 9.7 x 10(-8) and <= 10(-8), relative to H-2, for HCl and HF, respectively. Conclusions. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen in the wind.

stars: individual: W Aql

circumstellar matter

stars: AGB and post-AGB

stars: individual: chi Cyg

submillimeter: stars

Author

T. Danilovich

KU Leuven

M. van de Sande

KU Leuven

J. M. C. Plane

University of Leeds

T. J. Millar

Queen's University Belfast

P. Royer

KU Leuven

M. A. Amor

Université de Tunis El Manar

K. Hammami

Université de Tunis El Manar

L. Decock

KU Leuven

C. A. Gottlieb

Harvard-Smithsonian Center for Astrophysics

L. Decin

KU Leuven

University of Leeds

A. M. S. Richards

University of Manchester

Elvire De Beck

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

A. Baudry

University of Bordeaux

J. Bolte

KU Leuven

E. Cannon

KU Leuven

F. De Ceuster

KU Leuven

A. de Koter

University of Amsterdam

KU Leuven

S. Etoka

University of Manchester

D. Gobrecht

KU Leuven

M. Gray

National Astronomical Research Institute of Thailand

University of Manchester

F. Herpin

University of Bordeaux

W. Homan

KU Leuven

Université libre de Bruxelles (ULB)

M. Jeste

Max-Planck Institute for Radio Astronomy

P. Kervella

Paris Observatory

Theo Khouri

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

E. Lagadec

University of Côte d'Azur

S. Maes

KU Leuven

J. Malfait

KU Leuven

I. McDonald

Open University

University of Manchester

K. M. Menten

Max-Planck Institute for Radio Astronomy

M. Montarges

Paris Descartes University

H. S. P. Mueller

University of Cologne

B. Pimpanuwat

National Astronomical Research Institute of Thailand

University of Manchester

R. Sahai

California Institute of Technology (Caltech)

S. H. J. Wallstroem

KU Leuven

L. B. F. M. Waters

Netherlands Institute for Space Research (SRON)

Radboud University

K. T. Wong

Institut de Radioastronomie Millimétrique (IRAM)

J. Yates

University College London (UCL)

A. Zijlstra

University of Manchester

The University of Hong Kong

Astronomy and Astrophysics

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

Vol. 655 A80

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Geochemistry

DOI

10.1051/0004-6361/202141757

More information

Latest update

12/7/2021