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ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star pi(1)Gruis: I. First detection of a new companion and its effect on the inner wind

Homan, W; Montarges, M; Pimpanuwat, B; Richards, AMS; Wallstrom, SHJ; Kervella, P; Decin, L; ... Mueller, HSP; + view all (2020) ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star pi(1)Gruis: I. First detection of a new companion and its effect on the inner wind. Astronomy & Astrophysics , 644 , Article A61. 10.1051/0004-6361/202039185. Green open access

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Abstract

The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch (AGB) star π1Gruis, which has a known companion at ∼440 au and is thought to harbour a second, closer-by (< 10 au) companion, was observed with the Atacama Large Millimeter/submillimeter Array as part of the ATOMIUM Large programme. In this work, the brightest CO, SiO, and HCN molecular line transitions are analysed. The continuum map shows two maxima, separated by 0.04″ (6 au). The CO data unambiguously reveal that π1Gru’s circumstellar environment harbours an inclined, radially outflowing, equatorial density enhancement. It contains a spiral structure at an angle of ∼38 ± 3° with the line-of-sight. The HCN emission in the inner wind reveals a clockwise spiral, with a dynamical crossing time of the spiral arms consistent with a companion at a distance of 0.04″ from the AGB star, which is in agreement with the position of the secondary continuum peak. The inner wind dynamics imply a large acceleration region, consistent with a beta-law power of ∼6. The CO emission suggests that the spiral is approximately Archimedean within 5″, beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.5″ exhibits signatures of gas in rotation, which is found to fit the expected behaviour of gas in the wind-companion interaction zone. An investigation of SiO maser emission reveals what could be a stream of gas accelerating from the surface of the AGB star to the companion. Using these dynamics, we have tentatively derived an upper limit on the companion mass to be ∼1.1 M⊙.

Type: Article
Title: ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star pi(1)Gruis: I. First detection of a new companion and its effect on the inner wind
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/202039185
Publisher version: http://dx.doi.org/10.1051/0004-6361/202039185
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: line: profiles, stars: AGB and post-AGB, submillimeter: stars, circumstellar matter, BIPOLAR PREPLANETARY NEBULAE, MASS-LOSS, S-STARS, CIRCUMSTELLAR ENVELOPES, PLANETARY-NEBULA, ELECTRIC-DIPOLE, BINARY-SYSTEMS, DUSTY WINDS, RED GIANTS, SIO
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Computer Science
URI: https://discovery.ucl.ac.uk/id/eprint/10121741
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