An accreting dwarf star orbiting the S-type giant star π1 Gru
Artikel i vetenskaplig tidskrift, 2025
Context. At the end of their lives, low- to intermediate-mass stars reach the asymptotic giant branch (AGB), during which their photospheres expand by up to several hundred times and strong stellar winds develop. These changes lead to various interactions with celestial bodies in their close circumstellar environments, including mass- and angular-momentum transfer.
Aims. We aim to characterize the properties of the inner companion of the S-type AGB star π1 Gru and to identify plausible future evolutionary scenarios for this triple system.
Methods. We observed π1 Gru with the Atacama Large Millimeter/sub-millimeter Array (ALMA) and the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument of the Very Large Telescope (VLT), collected archival photometric data, and used the HIPPARCOS-Gaia proper motion anomaly. We derived the best orbital parameters using Bayesian inference.
Results. In June-July 2019, the inner companion, π1 Gru C, was located at 37.4±2.0mas from the primary (a projected separation of 6.05±0.55 au at 161.7±11.7 pc). The best orbital solution yields a companion mass of 0.86+0.22-0.20 M' (using the derived mass of the primary) and a semi-major axis of 7.050.57+0.54 au, corresponding to an orbital period of 11.0-1.5+1.7 yr. The preferred solution is an elliptical orbit with eccentricity e= 0.35-0.17+0.18, although a circular orbit cannot be fully excluded. The close companion could be either a K1VK7VF9.5V star or a white dwarf (WD). Ultraviolet and millimeter continuum photometry are consistent with the presence of an accretion disk around the close companion. The ultraviolet emission may originate from hot spots in an overall cooler disk, or from a hot disk if the companion is a WD.
Conclusions. Although the close companion and the AGB star are interacting and an accretion disk is observed around the companion, the mass-accretion rate is too low to trigger a Type Ia supernova, but it could produce novæevery 900 yr. Short-wavelength, spatially resolved observations are required to further constrain the nature of the C companion. Searches for close-in companions similar to this system will improve our understanding of the physics of mass and angular momentum transfer, as well as orbital evolution during late evolutionary stages.
Aims. We aim to characterize the properties of the inner companion of the S-type AGB star π1 Gru and to identify plausible future evolutionary scenarios for this triple system.
Methods. We observed π1 Gru with the Atacama Large Millimeter/sub-millimeter Array (ALMA) and the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument of the Very Large Telescope (VLT), collected archival photometric data, and used the HIPPARCOS-Gaia proper motion anomaly. We derived the best orbital parameters using Bayesian inference.
Results. In June-July 2019, the inner companion, π1 Gru C, was located at 37.4±2.0mas from the primary (a projected separation of 6.05±0.55 au at 161.7±11.7 pc). The best orbital solution yields a companion mass of 0.86+0.22-0.20 M' (using the derived mass of the primary) and a semi-major axis of 7.050.57+0.54 au, corresponding to an orbital period of 11.0-1.5+1.7 yr. The preferred solution is an elliptical orbit with eccentricity e= 0.35-0.17+0.18, although a circular orbit cannot be fully excluded. The close companion could be either a K1VK7VF9.5V star or a white dwarf (WD). Ultraviolet and millimeter continuum photometry are consistent with the presence of an accretion disk around the close companion. The ultraviolet emission may originate from hot spots in an overall cooler disk, or from a hot disk if the companion is a WD.
Conclusions. Although the close companion and the AGB star are interacting and an accretion disk is observed around the companion, the mass-accretion rate is too low to trigger a Type Ia supernova, but it could produce novæevery 900 yr. Short-wavelength, spatially resolved observations are required to further constrain the nature of the C companion. Searches for close-in companions similar to this system will improve our understanding of the physics of mass and angular momentum transfer, as well as orbital evolution during late evolutionary stages.
Stars: mass-loss
Circumstellar matter
Stars: imaging
Stars: AGB and post-AGB
Binaries: close
Stars: individual: pi1 Gru
Författare
M. Montargès
Observatoire de Paris
J. Malfait
KU Leuven
M. Esseldeurs
KU Leuven
A. de Koter
KU Leuven
Anton Pannekoek Institute for Astronomy
F. Baron
Georgia State University
P. Kervella
Observatoire de Paris
Taissa Danilovich
KU Leuven
Monash University
ARC Centre of Excellence for All-sky Astrophysics
A.M.S. Richards
University of Manchester
R. Sahai
California Institute of Technology (Caltech)
I. McDonald
University of Manchester
Open University
Theo Khouri
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
S. Shetye
KU Leuven
A. Zijlstra
University of Manchester
Macquarie University
M. Van De Sande
Universiteit Leiden
I. El Mellah
Universidad de Santiago de Chile
Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS)
F. Herpin
Laboratoire d'Astrophysique de Bordeaux
L. Siess
Université libre de Bruxelles (ULB)
S. Etoka
University of Manchester
D. Gobrecht
Göteborgs universitet
L. Marinho
Laboratoire d'Astrophysique de Bordeaux
Sofia Wallström
KU Leuven
K. T. Wong
Uppsala universitet
J. A. Yates
University College London (UCL)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 699 A22The Origin and Fate of Dust in Our Universe
Knut och Alice Wallenbergs Stiftelse (KAW 2020.0081), 2021-07-01 -- 2026-06-30.
Knut och Alice Wallenbergs Stiftelse (KAW 2019.0443), 2020-06-01 -- 2023-05-31.
Ämneskategorier (SSIF 2025)
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/202452587