TY - JOUR
T1 - Atomium
T2 - A high-resolution view on the highly asymmetric wind of the AGB star Pi1 Gruis. I. First detection of a new companion and its effect on the inner wind
AU - Homan, Ward
AU - Montarges, Miguel
AU - Pimpanuwat, Bannawit
AU - Richards, Anita M. S.
AU - Wallstrom, Sofia H. J.
AU - Kervella, Pierre
AU - Decin, Leen
AU - Zijlstra, Albert
AU - Danilovich, Taissa
AU - Koter, Alex de
AU - Menten, Karl
AU - Sahai, Raghvendra
AU - Plane, John
AU - Lee, Kelvin
AU - Waters, Rens
AU - Baudry, Alain
AU - Wong, Ka Tat
AU - Millar, Tom J.
AU - Sande, Marie Van de
AU - Lagadec, Eric
AU - Gobrecht, David
AU - Yates, Jeremy
AU - Price, Daniel
AU - Cannon, Emily
AU - Bolte, Jan
AU - Ceuster, Frederik De
AU - Herpin, Fabrice
AU - Nuth, Joe
AU - Sindel, Jan Philip
AU - Kee, Dylan
AU - Grey, Malcolm D.
AU - Etoka, Sandra
AU - Jeste, Manali
AU - Gottlieb, Carl A.
AU - Gottlieb, Elaine
AU - McDonald, Iain
AU - Mellah, Ileyk El
AU - Muller, Holger S. P.
N1 - Funding Information:
Acknowledgements. We would like to sincerely thank the Referee, whose constructive suggestions have substantially improved the paper. This paper makes use of uses the following ALMA data: ADS/JAO.ALMA#2018.1.00659.L, “ATOMIUM: ALMA tracing the origins of molecules forming dust in oxygen-rich M-type stars”. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NR.A.O, and NAOJ. W.H., S.H.J.W., L.D., M.M. acknowledge support from the ERC consolidator grant 646758 AEROSOL. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant agreement No. 665501 with the research Foundation Flanders (FWO) ([PEGASUS]2 Marie Curie fellowship 12U2717N awarded to M.M.). TD acknowledges support from the Research Foundation Flanders (FWO) through grant 12N9920N. TJM is grateful to the STFC for support via grant number ST/P000312/1. JMCP acknowledges funding from the UK STFC (grant number ST/T000287/1) MVdS acknowledges support from the Research Foundation Flanders (FWO) through grant 12X6419N. S.E. acknowledges funding from the UK Science and Technology Facilities Council (STFC) as part of the consolidated grant ST/P000649/1 to the Jodrell Bank Centre for Astrophysics at the University of Manchester. We acknowledge financial support from “Programme National de Physique Stel-laire” (PNPS) of CNRS/INSU, France. We used the SIMBAD and VIZIER databases at the CDS, Strasbourg (France) (http://cdsweb.u-strasbg.fr/), and NASA’s Astrophysics Data System Bibliographic Services. This research made use of IPython (Pérez & Granger 2007), Numpy (van der Walt et al. 2011), Matplotlib (Hunter 2007), SciPy (Virtanen et al. 2020), and Astropy (http:// www.astropy.org/), a community-developed core Python package for Astronomy (Astropy Collaboration 2013).
Publisher Copyright:
© ESO 2020.
PY - 2020/12/1
Y1 - 2020/12/1
N2 - 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 0.0400 (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 0.0400 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 500, beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.500 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⊙.
AB - 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 0.0400 (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 0.0400 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 500, beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.500 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⊙.
KW - Circumstellar matter
KW - Line: Profiles
KW - Stars: AGB and post-AGB
KW - Submillimeter: Stars
U2 - 10.1051/0004-6361/202039185
DO - 10.1051/0004-6361/202039185
M3 - Article
SN - 0004-6361
VL - 644
JO - A&A
JF - A&A
M1 - A61
ER -