X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars
Journal article, 2026
Aims. The goal of this study is to further the understanding of the wind formation mechanism in asymptotic giant branch (AGB) stars through the analysis of the close environment (within a few stellar radii) of the carbon star X TrA. Methods. X TrA was observed for the first time with the Mid-Infrared SpectroScopic Experiment instrument (MATISSE) in the L and N bands in low spectral resolution mode (R=30), and its close surroundings were mapped in specific wavelength ranges corresponding to specific molecules (C2 H2 and HCN, at 3.1 and 3.8 μm) and dust (amorphous carbon and, for example, SiC at 11.3 μm), via image reconstruction techniques. Results. The angular diameter of the star ranges from 10 mas in the L band pseudo-continuum (3.5 μm) to 20 mas at 3.1 and 11.3 μm. The reconstructed images show some mild elongated features (along the east-west direction) and asymmetric protrusions, which are most evident around 3.1 μm. Imaging results highlight the clumpy nature of the circumstellar environment, starting from the photospheric region up to more distant layers. Conclusions. The angular diameters found for X TrA in the image data are in agreement with previous photospheric diameter estimates (following VLTI/MIDI 8-13 μm observations), and their wavelength dependence is similar to values found for other carbon stars observed with MATISSE (R Scl and V Hya). The 3.1 μm images presented here show highly asymmetric features, another case of a C-rich star with irregular morphologies close to the stellar disk; this supports the notion that the C2 H2 + HCN abundance distribution usually originates from a clumpy layer around carbon stars.
Stars: mass-loss
Stars: winds, outflows
Stars: AGB and post-AGB
Techniques: interferometric
Circumstellar matter
Author
V. Rǎstǎu
University of Vienna
C. Paladini
European Southern Observatory Santiago
J. Drevon
European Southern Observatory Santiago
J. Hron
University of Vienna
F. Kerschbaum
University of Vienna
M. Wittkowski
European Southern Observatory (ESO)
J.P. Fonfría
Spanish National Research Council (CSIC)
M. Montargès
Paris Observatory
Theo Khouri
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Wouter Vlemmings
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Hans Olofsson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
K. Ohnaka
Universidad Andrés Bello
J. Alonso-Hernandez
Centro de Astrobiologia (CAB)
C. S. Contreras
Centro de Astrobiologia (CAB)
Luis Velilla Prieto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
W. Danchi
National Aeronautics and Space Administration (NASA)
G. Rau
National Science Foundation
Schmidt Sciences
F. Lykou
Hungarian Academy of Sciences
J. Sanchez-Bermudez
Universidad Nacional Autónoma de México
B. Lopez
Observatoire de la Cote d'Azur
S. Höfner
Uppsala University
B. Aringer
University of Vienna
Léa Planquart
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
P. Cruzalèbes
Observatoire de la Cote d'Azur
G. Weigelt
Max Planck Society
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 705 A127Opticon RadioNet Pilot (ORP)
European Commission (EC) (EC/H2020/101004719), 2021-03-01 -- 2025-02-28.
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202557477