Issue |
A&A
Volume 671, March 2023
|
|
---|---|---|
Article Number | A129 | |
Number of page(s) | 12 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202245039 | |
Published online | 15 March 2023 |
Spectroscopic and interferometric signatures of magnetospheric accretion in young stars
1
Univ. Grenoble Alpes, CNRS, IPAG, 38000
Grenoble, France
e-mail: benjamin.tessore@univ-grenoble-alpes.fr
2
School of Physics and Astronomy, Monash University, VIC, 3800
Australia
Received:
22
September
2022
Accepted:
30
January
2023
Aims. We aim to assess the complementarity between spectroscopic and interferometric observations in the characterisation of the inner star-disc interaction region of young stars.
Methods. We used the MCFOST code to solve the non-local thermodynamic equilibrium problem of line formation in non-axisymmetric accreting magnetospheres. We computed the Brγ line profile originating from accretion columns for models with different magnetic obliquities. We also derived monochromatic synthetic images of the Brγ line-emitting region across the line profile. This spectral line is a prime diagnostic of magnetospheric accretion in young stars and is accessible with the long baseline near-infrared interferometer GRAVITY installed at the ESO Very Large Telescope Interferometer.
Results. We derive Brγ line profiles as a function of rotational phase and compute interferometric observables, visibilities, and phases, from synthetic images. The line profile shape is modulated along the rotational cycle, exhibiting inverse P Cygni profiles at the time the accretion shock faces the observer. The size of the line’s emission region decreases as the magnetic obliquity increases, which is reflected in a lower line flux. We apply interferometric models to the synthetic visibilities in order to derive the size of the line-emitting region. We find the derived interferometric size to be more compact than the actual size of the magnetosphere, ranging from 50 to 90% of the truncation radius. Additionally, we show that the rotation of the non-axisymmetric magnetosphere is recovered from the rotational modulation of the Brγ-to-continuum photo-centre shifts, as measured by the differential phase of interferometric visibilities.
Conclusions. Based on the radiative transfer modelling of non-axisymmetric accreting magnetospheres, we show that simultaneous spectroscopic and interferometric measurements provide a unique diagnostic to determine the origin of the Brγ line emitted by young stellar objects and are ideal tools to probe the structure and dynamics of the star-disc interaction region.
Key words: line: profiles / stars: variables: T Tauri, Herbig Ae/Be / accretion, accretion disks
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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