Centre de Recherche Astrophysique de Lyon
Advisors Ferreol Soulez (CRAL, Lyon) Jean-Philippe Berger (IPAG, Grenoble)
Keywords: Inverse problems, High-Contrast Imaging, Sparse Aperture Masking, Circumstellar environnement
Contact ferreol.soulez@univ-lyon1.fr
Potential for a follow-up as a PhD thesis
Scientific context:
The study of the morphology of protoplanetary disks at very high angular resolution in the infrared provides essential information for understanding the physical processes leading to the formation of an exoplanetary system. High-contrast coronagraphic imaging reveals large-scale structures in the disks, revealing dynamic structures such as spiral waves or cavities, as well as young planets. This comes at the cost of sacrificing imaging of the central astronomical units hidden by the coronagraphic mask, preventing observation of the inner disk and a possible habitable zone. Long baseline interferometry observations at the Very Large Telescope Interferometer (VLTI) allow us to constrain the morphology of disks very close to the star, but suffer from a lack of information at low frequencies (i.e., at large spatial scales). Pupil masking technique [1], combined with high-contrast imaging, has been developed to enhance the capabilities of single-aperture telescopes by removing the need for a coronagraphic mask. Theoretically, it allows us to image within the Rayleigh resolution limit of the star (surpassing coronagraphy) and provides data that is perfectly complementary to both coronagraphy and long-baseline interferometry. Many high-contrast imaging instruments include a pupil mask (e.g., VLT-SPHERE-SAM, JWST-NIRISS-AMI, MICADO-ELT) [2,3,4]. However, real-world performance remains limited, and fundamental aspects and limiting factors of this technique are still poorly understood—especially for ground-based instruments, which are affected by atmospheric disturbances. This calls into question the purely interferometric approach typically used for data processing.
Research Project
In this project, we aim to demonstrate that by treating pupil masking data processing as an image deconvolution problem with a structured point spread function (PSF), it is possible to achieve higher contrast than with the standard interferometric approach. We propose to model the signal (coherent flux, interference patterns) directly in the image plane. This should allow more effective detection of planetary companions or dynamic disk disturbances in young stellar systems. During the internship, we will work with data from the VLT-SPHERE-IRDIS-SAM instrument, focusing on young transitional disks, which are strongly suspected of hosting forming planets.
The work will be structured in several phases:
— Analytical modeling of the instrument, taking into account its characteristics. Starting from the image formation equation, we will assess how various imperfections affect the final image dynamics. To do this, we will compare simulation results with available calibration data.
— Using IRDIS-SAM calibration data, we will establish performance curves, expressed as contrast profiles as a function of angular separation.
— Finally, we will simulate astrophysical images of transitional protoplanetary disks with embedded planets, degraded by the instrument model, to determine what astrophysical features can be recovered.
In addition to its immediate impact on our understanding of protoplanetary disk structure, this research effort and the tools developed could have a significant future impact—particularly in preparation for the commissioning of the ELT (with the MICADO instrument) or for better exploitation of the pupil mask on the JWST.
The research project is a collaboration between:
CRAL, with deep expertise in the SPHERE instrument and interferometric data processing
IPAG, which has led a long-standing program of very high angular resolution observations of protoplanetary environments using both pupil masking and long-baseline interferometry
References:
[1] Lacour, Sylvestre, et al. “Sparse aperture masking on Paranal.” The Messenger 146 (2011): 18-23.
[2] Cheetham, Anthony C., et al. “Sparse aperture masking with SPHERE.” Optical and Infrared Interferometry and Imaging V. Vol. 9907. SPIE, 2016.
[3] Artigau, Étienne, et al. “NIRISS aperture masking interferometry: an overview of science opportunities.” Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave 9143 (2014): 1185-1194.
[4] Huby, Elsa, et al. “The MICADO first light imager for the ELT: sparse aperture masks, design, and simulations.” Ground-based and Airborne Instrumentation for Astronomy X. Vol. 13096. SPIE, 2024.
Nature of the financial support for the internship: PEPR Origin or team funding
