Dust distribution and mass transfer in π1 Gru with VLTI/MATISSE: Revealing dust formation and wind shaping by companion

Abstract: Asymptotic Giant Branch (AGB) stars are among the primary sources of dust in the Galaxy and play a critical role in enriching the interstellar medium with heavy elements. Despite their importance, the physical mechanisms driving dust formation and mass loss in these evolved stars remain poorly understood. Key processes take place within a few stellar radii from the surface, where temperatures and densities allow the formation of molecules and dust precursors. High-angular-resolution interferometric observations are essential to probe this region in detail. Recent VLTI/MATISSE observations of the S-type AGB star Pi.01 Gruis in the L- and N-bands, combined with image reconstruction techniques, have revealed highly complex atmospheric dynamics and surface structures. The images show inhomogeneous, clumpy dust and molecular distributions around the star, indicating that dust formation is not spherically symmetric. In addition, indirect evidence of a binary companion was detected, with clear signatures of mass transfer from the AGB star. This binary interaction appears to significantly influence the morphology of the circumstellar environment and may enhance localized dust production. The presentation will discuss the implications of these findings on dust formation scenarios and will highlight spatial and spectral variations of molecular features relative to the continuum emission.