Direct imaging of mass transfer and circumcompanion structures in π1 Gru with VLTI/MATISSE
Journal article, 2026
Aims. We investigate how the presence of a binary companion appears to affect dust and molecule formation in the circumstellar environment of a star on the asymptotic giant branch (AGB). Methods.L- and N-band observations obtained over the course of one month with the multi aperTure mid-infrared spectroScopic experiment instrument (MATISSE) at the very large telescope interferometer (VLTI) were used to constrain the distribution of dust and molecules in the close environment of π1 Gru through image reconstruction. The reconstructed images were fit to the interferometric observables, that is, the visibilities and closure phases, using the two Python-based tools Python for MiRA (PYRA) and mean astrophysical images with PYRA (MYTHRA) built around the multi-aperture image reconstruction algorithm (MiRA). Results. Our observations support (i) a wind Roche-lobe overflow (WRLOF) scenario, where mass transfer from the AGB star to its companion produces a possible circumcompanion disk in the L band around π1 Gru C, with a central cavity that likely traces dust sublimation and a circumcompanion envelope in the N band. (ii) A main-sequence nature for the companion: Because both Atacama large millimeter/submillimeter array (ALMA) and the VLTI/MATISSE N-band observations show emission, we favor a thermal infrared emission from the main-sequence star over free-free emission from a with dwarf companion. Finally, (iii) a plume-like structure extending from π1 Gru C, likely marking the onset of the spiral observed at larger scales. Together, this provides direct evidence that links small-scale mass transfer and disk formation through WRLOF to the global circumstellar morphology. Conclusions. These results highlight the atmospheric deformation induced by the companion, reveal ongoing mass transfer between the evolved star and its companion, and indicate a circumcompanion disk-like structure.
Stars: mass-loss
Binaries: close
Stars: imaging
Stars: AGB and post-AGB
Stars: atmospheres
Circumstellar matter
Author
J. Drevon
European Southern Observatory Santiago
C. Paladini
European Southern Observatory Santiago
S. Höfner
Uppsala University
Léa Planquart
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Université libre de Bruxelles (ULB)
L. Siess
Université libre de Bruxelles (ULB)
A. Jorissen
Université libre de Bruxelles (ULB)
M. Montargès
Paris Observatory
Wouter Vlemmings
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Theo Khouri
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Hans Olofsson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
J. Alonso-Hernandez
Centro de Astrobiologia (CAB)
Elvire De Beck
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
J.P. Fonfría
Spanish National Research Council (CSIC)
J. Hron
University of Vienna
A. Matter
Observatoire de la Cote d'Azur
N. Nardetto
Observatoire de la Cote d'Azur
K. Ohnaka
Universidad Andrés Bello
C. S. Contreras
Centro de Astrobiologia (CAB)
G. Weigelt
Max Planck Society
M. Wittkowski
European Southern Observatory (ESO)
Behzad Bojnordiarbab
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
B. Aringer
University of Vienna
F. Baron
Georgia State University
A. Chiavassa
Max Planck Society
Observatoire de la Cote d'Azur
P. Cruzalèbes
Observatoire de la Cote d'Azur
W. Danchi
Schmidt Sciences
F. Kerschbaum
University of Vienna
J. Leftley
Observatoire de la Cote d'Azur
E. Lagadec
Observatoire de la Cote d'Azur
B. Lopez
Observatoire de la Cote d'Azur
F. Lykou
Hungarian Academy of Sciences
F. Millour
Observatoire de la Cote d'Azur
G. Rau
National Science Foundation
Schmidt Sciences
J. Sanchez-Bermudez
Universidad Nacional Autónoma de México
F. Thévenin
Observatoire de la Cote d'Azur
S. Van Eck
Université libre de Bruxelles (ULB)
L. Velilla-Prieto
Spanish National Research Council (CSIC)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 706 L1Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202558298