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The extended molecular envelope of the asymptotic giant branchstar π1 Gruis as seen by ALMA: I. Large-scale kinematic structure and CO excitation properties
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Department of Earth and Space Sciences, Chalmers University of Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A28Article in journal (Refereed) Published
Abstract [en]

Context. The S-type asymptotic giant branch (AGB) star pi(1) Gru has a known companion at a separation of 2 ''.7 (approximate to 400 AU). Previous observations of the circumstellar envelope (CSE) show strong deviations from spherical symmetry. The envelope structure, including an equatorial torus and a fast bipolar outflow, is rarely seen in the AGB phase and is particularly unexpected in such a wide binary system. Therefore a second, closer companion has been suggested, but the evidence is not conclusive.

Aims. The aim is to make a 3D model of the CSE and to constrain the density and temperature distribution using new spatially resolved observations of the CO rotational lines.

Methods. We have observed the J = 3-2 line emission from (CO)-C-12 and (CO)-C-13 using the compact arrays of the Atacama Large Millimeter/submillimeter Array (ALMA). The new ALMA data, together with previously published (CO)-C-12 J = 2-1 data from the Submillimeter Array (SMA), and the (CO)-C-12 J = 5-4 and J = 9-8 lines observed with Herschel/Heterodyne Instrument for the Far-Infrared (HIFI), is modeled with the 3D non-LTE radiative transfer code SHAPEMOL.

Results. The data analysis clearly confirms the torus-bipolar structure. The 3D model of the CSE that satisfactorily reproduces the data consists of three kinematic components: a radially expanding torus with velocity slowly increasing from 8 to 13 km s(-1) along the equator plane; a radially expanding component at the center with a constant velocity of 14 km s(-1); and a fast, bipolar outflow with velocity proportionally increasing from 14 km s(-1) at the base up to 100 km s(-1) at the tip, following a linear radial dependence. The results are used to estimate an average mass-loss rate during the creation of the torus of 7.7 x 10(-7) M-circle dot yr(-1). The total mass and linear momentum of the fast outflow are estimated at 7.3 x 10(-4) M-circle dot and 9.6 x 10(37) g cm s(-1), respectively. The momentum of the outflow is in excess (by a factor of about 20) of what could be generated by radiation pressure alone, in agreement with recent findings for more evolved sources. The best-fit model also suggests a (CO)-C-12/(CO)-C-13 abundance ratio of 50. Possible shaping scenarios for the gas envelope are discussed.

Place, publisher, year, edition, pages
2017. Vol. 605, article id A28
Keywords [en]
stars: AGB and post-AGB; stars: mass-loss; stars: individual: pi(1) Gru; stars: general; radio lines: stars; binaries: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-327430DOI: 10.1051/0004-6361/201730703ISI: 000412231200057OAI: oai:DiVA.org:uu-327430DiVA, id: diva2:1130783
Funder
EU, European Research Council, 614264Available from: 2017-08-11 Created: 2017-08-11 Last updated: 2018-01-12Bibliographically approved
In thesis
1. The circumstellar envelope of the S-type AGB star π1 Gruis
Open this publication in new window or tab >>The circumstellar envelope of the S-type AGB star π1 Gruis
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2017. p. 51
Keywords
AGB and post-AGB stars: mass-loss binaries: general - radio lines: stars - stars: general stars: individual: π1 Gru.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-327397 (URN)
Presentation
2017-08-01, 80115, Lägerhyddsvägen 1, 752 37 Uppsala, Uppsala, 10:15 (English)
Opponent
Available from: 2017-08-11 Created: 2017-08-10 Last updated: 2017-08-11Bibliographically approved

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Doan, LamRamstedt, SofiaHöfner, Susanne

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