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HD 101584: circumstellar characteristics and evolutionary status
Chalmers Univ Technol, Dept Space Earth & Environm, Onsala Space Observ, S-43992 Onsala, Sweden.
Chalmers Univ Technol, Dept Space Earth & Environm, Onsala Space Observ, S-43992 Onsala, Sweden.
Chalmers Univ Technol, Dept Space Earth & Environm, Onsala Space Observ, S-43992 Onsala, Sweden.
Chalmers Univ Technol, Dept Space Earth & Environm, Onsala Space Observ, S-43992 Onsala, Sweden.
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 623, article id A153Article in journal (Refereed) Published
Abstract [en]

Context: There is growing evidence that red giant evolution is often affected by an interplay with a nearby companion, in some cases taking the form of a common-envelope evolution.

Aims: We have performed a study of the characteristics of the circumstellar environment of the binary object HD 101584, that provides information on a likely evolutionary scenario.

Methods: We have obtained and analysed ALMA observations, complemented with observations using APEX, of a large number of molecular lines. An analysis of the spectral energy distribution has also been performed.

Results: Emissions from 12 molecular species (not counting isotopologues) have been observed, and most of them mapped with angular resolutions in the range 0 ''.1-0 ''.6. Four circumstellar components are identified: (i) a central compact source of size approximate to 0 ''.15, (ii) an expanding equatorial density enhancement (a flattened density distribution in the plane of the orbit) of size approximate to 3 '', (iii) a bipolar high-velocity outflow (approximate to 150 km s(-1)), and (iv) an hourglass structure. The outflow is directed almost along the line of sight. There is evidence of a second bipolar outflow. The mass of the circumstellar gas is approximate to 0.5 [D/1 kpc](2) M-circle dot, about half of it lies in the equatorial density enhancement. The dust mass is approximate to 0.01 [D/1 kpc](2) M-circle dot, and a substantial fraction of this is in the form of large-sized, up to 1 mm, grains. The estimated kinetic age of the outflow is approximate to 770 [D/1 kpc] yr. The kinetic energy and the scalar momentum of the accelerated gas are estimated to be 7 x 10(45) [D/1 kpc](2) erg and 10(39) [D/1 kpc](2) g cm s(-1), respectively.

Conclusions: We provide good evidence that the binary system HD 101584 is in a post-common-envelope-evolution phase, that ended before a stellar merger. Isotope ratios combined with stellar mass estimates suggest that the primary star's evolution was terminated already on the first red giant branch (RGB). Most of the energy required to drive the outflowing gas was probably released when material fell towards the companion.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2019. Vol. 623, article id A153
Keywords [en]
circumstellar matter, stars: individual: HD101584, stars: AGB and post-AGB, binaries: close, radio lines: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-381122DOI: 10.1051/0004-6361/201834897ISI: 000462115700001OAI: oai:DiVA.org:uu-381122DiVA, id: diva2:1302310
Funder
Swedish Research CouncilEU, European Research Council, 614264Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-08-22Bibliographically approved
In thesis
1. Companion wind shaping in binaries involving an AGB star
Open this publication in new window or tab >>Companion wind shaping in binaries involving an AGB star
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stars of initial masses between 0.8-8 M☉ will become "asymptotic giant branch" (AGB) stars during the final stages of their evolution. During this phase, the stars are characterized by low velocity and high-density winds. An AGB star can lose a substantial fraction of its mass through the stellar wind and thereby avoid ending up as a supernova explosion. The AGB stars, therefore, play an important role in enriching the interstellar medium (ISM) with chemical elements and in contributing dust and gas to the ISM. The mass-loss rate on the AGB is a decisive parameter for the lifetime of this evolutionary phase and the fate of low- and intermediate-mass stars. An accurate mass-loss-rate estimation provides an important constraint for wind models aimed to better understand the wind-driving mechanism, as well as for stellar evolution.

The stellar wind is driven by radiation pressure on dust grains and blows away dust and gas from the central star. This creates an extended envelope which is expected to be spherical because of the isotropic radiation field of the central star, and the connection between the radiation field and the wind. However, there is growing observational evidence of asymmetrical morphology, e.g., torii, jets, bipolar outflows, in AGB circumstellar envelopes (CSEs). Moreover, proto-planetary nebulae (proto-PNe) and PNe, the next evolutionary phase after the AGB phase, show a wide range of asymmetrical morphologies. In many cases, an embedded binary system has been detected in the gas envelopes. This is pointing to the gravitational effect of the companion as important for the envelope shaping mechanism.

The work that this thesis is based on, studies two interesting examples of (post) AGB stars which show complex morphologies of their CSEs. The S-star π1 Gruis shows a CSE structure consisting of an equatorial low-velocity expanding spiral and a fast bipolar outflow. The circumstellar environment of the post-AGB (or post red giant branch, post-RGB) star HD 101584 shows an equatorial density enhancement and a high-velocity bipolar outflow. Same conclusions are drawn for both cases; that the radiation pressure on the dust cannot support the observed energetic outflows, and that interaction with the companions are proposed to shape the envelopes and accelerate the gas.

The thesis gives a brief introduction on AGB stars and wind shaping mechanisms of AGB CSEs. The thesis also presents the principles of interferometry, the data reduction methods, and the radiative transfer calculations used in the studies. Results from the included papers are also discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1845
Keywords
AGB and post-AGB stars, mass-loss, radio lines, binaries, wind shaping
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-391354 (URN)978-91-513-0728-2 (ISBN)
Public defence
2019-10-09, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-09-17 Created: 2019-08-22 Last updated: 2019-10-15

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