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DEATHSTAR: Nearby A...
DEATHSTAR: Nearby AGB stars with the Atacama Compact Array: II. CO envelope sizes and asymmetries: The S-type stars
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- Andriantsaralaza, Miora (author)
- Uppsala universitet,Teoretisk astrofysik,Koninklijke Sterrenwacht van Belgie, Ringlaan 3, B-1180 Brussels, Belgium.
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- Ramstedt, Sofia (author)
- Uppsala universitet,Teoretisk astrofysik
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- Vlemmings, Wouter, 1974 (author)
- Chalmers tekniska högskola,Chalmers University of Technology,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Danilovich, Taissa, 1987 (author)
- Katholieke Universiteit Leuven,Katholieke Univ Leuven, Dept Phys & Astron, Inst Astron, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
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- de Beck, Elvire, 1985 (author)
- Chalmers tekniska högskola,Chalmers University of Technology,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Groenewegen, M. A. T. (author)
- Royal Observatory of Belgium,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Höfner, Susanne (author)
- Uppsala universitet,Teoretisk astrofysik
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- Kerschbaum, F. (author)
- Universität Wien,University of Vienna,Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria.
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- Khouri, Theo, 1985 (author)
- Chalmers tekniska högskola,Chalmers University of Technology,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Lindqvist, Michael, 1960 (author)
- Uppsala universitet,Uppsala University,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Maercker, Matthias, 1979 (author)
- Chalmers tekniska högskola,Chalmers University of Technology,Univ Oslo, Rosseland Ctr Solar Phys, POB 1029, N-0315 Oslo, Norway.;Univ Oslo, Inst Theoret Astrophys, POB 1029, N-0315 Oslo, Norway.
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- Olofsson, Hans, 1952 (author)
- Chalmers tekniska högskola,Chalmers University of Technology,Chalmers Univ Technol, Onsala Space Observ, Dept Space Earth & Environm, S-43992 Onsala, Sweden.
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- Quintana-Lacaci, G. (author)
- CSIC - Instituto de Fisica Fundamental (IFF),CSIC, Grp Mol Astrophys, IFF, C Serrano 123, Madrid 28006, Spain.
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- Saberi, M. (author)
- Universitetet i Oslo,University of Oslo
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- Sahai, R. (author)
- CALTECH, Jet Prop Lab, MS 183-900, Pasadena, CA 91109 USA.
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- Zijlstra, A. (author)
- University of Manchester,Univ Manchester, Jodrell Bank Ctr Astrophys, Alan Turing Bldg, Manchester M13 9PL, Lancs, England.
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(creator_code:org_t)
- 2021-09-07
- 2021
- English.
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 653
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Abstract
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- Aims. We aim to constrain the sizes of, and investigate deviations from spherical symmetry in, the CO circumstellar envelopes (CSEs) of 16 S-type stars, along with an additional 7 and 4 CSEs of C-type and M-type AGB stars, respectively. Methods. We map the emission from the CO J = 2-1 and 3-2 lines observed with the Atacama Compact Array (ACA) and its total power (TP) antennas, and fit with a Gaussian distribution in the uv- and image planes for ACA-only and TP observations, respectively. The major axis of the fitted Gaussian for the CO(2-1) line data gives a first estimate of the size of the CO-line-emitting CSE. We investigate possible signs of deviation from spherical symmetry by analysing the line profiles and the minor-to-major axis ratio obtained from visibility fitting, and by investigating the deconvolved images. Results. The sizes of the CO-line-emitting CSEs of low-mass-loss-rate (low-MLR) S-type stars fall between the sizes of the CSEs of C-stars, which are larger, and those of M-stars, which are smaller, as expected because of the differences in their respective CO abundances and the dependence of the photodissociation rate on this quantity. The sizes of the low-MLR S-type stars show no dependence on circumstellar density, as measured by the ratio of the MLR to terminal outflow velocity, irrespective of variability type. The density dependence steepens for S-stars with higher MLRs. While the CO(2-1) brightness distribution size of the low-density S-stars is in general smaller than the predicted photodissociation radius (assuming the standard interstellar radiation field), the measured size of a few of the high-density sources is of the same order as the expected photodissociation radius. Furthermore, our results show that the CO CSEs of most of the S-stars in our sample are consistent with a spherically symmetric and smooth outflow. For some of the sources, clear and prominent asymmetric features are observed which are indicative of intrinsic circumstellar anisotropy. Conclusions. As the majority of the S-type CSEs of the stars in our sample are consistent with a spherical geometry, the CO envelope sizes obtained in this paper will be used to constrain detailed radiative transfer modelling to directly determine more accurate MLR estimates for the stars in our sample. For several of our sources that present signs of deviation from spherical symmetry, further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures. This will provide further insight into the mass-loss process and its related chemistry in S-type AGB stars.
Subject headings
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
- NATURVETENSKAP -- Fysik -- Annan fysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Other Physics Topics (hsv//eng)
- NATURVETENSKAP -- Matematik -- Sannolikhetsteori och statistik (hsv//swe)
- NATURAL SCIENCES -- Mathematics -- Probability Theory and Statistics (hsv//eng)
Keyword
- Stars: mass-loss
- Circumstellar matter
- Stars: winds
- outflows
- Stars: AGB and post-AGB
Publication and Content Type
- art (subject category)
- ref (subject category)
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Andriantsaralaza ...
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Ramstedt, Sofia
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Vlemmings, Woute ...
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Danilovich, Tais ...
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de Beck, Elvire, ...
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Groenewegen, M. ...
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Höfner, Susanne
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Kerschbaum, F.
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Khouri, Theo, 19 ...
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Lindqvist, Micha ...
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Maercker, Matthi ...
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Olofsson, Hans, ...
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Quintana-Lacaci, ...
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Saberi, M.
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Sahai, R.
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Zijlstra, A.
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