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 A80Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Geochemistry
DOI
10.1051/0004-6361/202141757