From Shadows to Hotspots: Imaging of Inner Protoplanetary Disc Structure

This thesis employs long-baseline near-infrared interferometry to characterise and image the innermost regions of protoplanetary discs, investigating disc geometry, accretion signatures, inner/outer disc misalignments, and temporal and azimuthal variability. Through these observations, I aim to target the dynamical processes that govern inner disc structure, providing observational constraints that advance both disc physics theory and planet formation models. Using CHARA/MIRC-X and VLTI/PIONIER data, I present my published paper with the first well-resolved characterisation of the innermost disc around the T Tauri star HD 143006. The outer disc is known to have multiple rings, gaps, and asymmetries. I confirm a 39° ± 4° misalignment between the inner and outer discs, which explains the narrow shadows observed in scattered-light images. This geometric constraint enables me to determine both the inner and outer disc orientations and estimate the outer disc scale height to be approximately 13%, which results in agreement with theoretical predictions. A search for the suspected stellar companion responsible for this misalignment rules out the hypothesised companion mass, and I establish an upper limit of 0.17M⊙ at separations of 0--8 au. I investigate temporal and azimuthal variability in the innermost region of the Herbig star MWC 480, motivated by the detection of NIR photometric variability in monitoring surveys. Four nights of CHARA/MIRC-X and CHARA/MYSTIC reveal consistent disc geometry (inclination, position angle, and size) across all epochs. Image reconstruction using OITOOLS (SPARCO method) reveals persistent over-brightness on the right-hand side of the rim, which is likely an inclination effect. The imaging results provide tentative evidence for hotspots rotating at half-Keplerian velocities. This adds to growing evidence from similar studies that inner disc hotspots rotate at sub-Keplerian speeds, potentially indicating the influence of a companion. Finally, I present a pilot study using R=4000 VLTI/GRAVITY observations of five Herbig stars - four of which have never been observed with optical interferometry – to characterise their innermost disc regions. I successfully derive inclination and position angles for all targets. Three objects in the sample were observed with small-baseline configurations, which prohibited the resolution of inner cavities for these objects. The sizes derived for these objects were larger than predicted by standard size-luminosity relations. The two resolved objects agree well with theoretical expectations and are consistent with emission from the sublimation front. I detect a tentative companion candidate in one system and identify Brγ emission signatures in two others, attributed to disc wind and accretion processes. These results demonstrate the scientific potential of inner disc surveys whilst highlighting the need for longer baseline configurations. This work demonstrates the transformative capabilities of long-baseline near-infrared interferometry for probing the structure and dynamics of protoplanetary discs. The diverse results across targets underscore the importance of individual disc characterisation, as the inherent complexity and uniqueness of these systems preclude generalisations. These interferometric observations provide unprecedented insight into innermost disc structure and dynamics, revealing the rich diversity of physical processes operating at previously inaccessible spatial scales.<p></p>

Author dc:creator

• Isabelle Codron (21374204)

• interferometry
• planet-disc interaction
• star-planet interaction
• star formation

Statement dc:rights

• All rights reserved
• Open Access after 2027-12-01

Identifier

10779/exe.32537037.v1

OAI identifier oai:identifier

oai:figshare.com:article/32537037