Multi-techniques observations of young T Tauri stars and prospects with the VLTI/GRAVITY+ instrument

PhD defense of Hugo Nowacki - Friday, December 13rd, 2024 à 14h - Manuel Forestini room IPAG

T Tauri stars are young Sun-like stars. Studying the processes that link these stars to their protoplanetary disks allows to constrain the mechanisms involved in the final stages of star formation and the environment in which planetary formation occurs. Therefore, these studies provide insights into the probable origins of our own solar system.
S CrA N and RU Lup are two particularly young T Tauri stars in which the study of accretion and ejection processes in the central regions allows to explore various aspects of stellar and planetary formation.

Using optical spectropolarimetric observations from CFHT/ESPaDOnS, I studied the complexity of the stellar magnetic field and inferred properties of the accretion structures and dynamics in these objects. Using near-infrared interferometric data from VLTI/GRAVITY, I reconstructed the geometry of the inner rim of the dusty disk and studied the gas dynamics in the vicinity of the star (within a 0.1 astronomical units radius). By comparing the results obtained from both observational techniques, I was able to explore exotic regimes of star formation and place constraints on future observations of such systems.

In parallel, I actively participated in the development of GRAVITY+. This project aims to improve the performance of GRAVITY, allowing us to deepen the analyses presented in this thesis by providing access to a much larger, less biased sample with unprecedented performance. I was particularly involved in the characterization and installation of the deformable mirror of the adaptive optics. I studied the sensitivity of the mirror and its mount to various environmental factors and participated in its installation at the Paranal Observatory in Chile in the summer of 2024. Based on the anticipated performance of GRAVITY, I also explored the new possibilities offered by optical interferometry for objects previously out of the reach of this technique, such as Class I objects. Finally, I explored several perspectives aimed at making the study of young stellar objects as routine, powerful, and meaningful as possible, in anticipation of the emergence of a new paradigm for statistical studies of T Tauri stars, heralded by the upcoming commissioning of GRAVITY+.

Thesis Direction

  • Karine Perraut and Jean-Baptiste Le Bouquin

The jury will consist of

  • Claude Catala, Senior researcher, Paris Observatory U. PSL, Referee
  • Franz Martinache, Associate Professor, Lagrange OCA, Referee
  • Anaëlle Maury, research engineer, AIM CEA Saclay, Examiner
  • Sylvie Cabrit, Astronomer, Observatoire de Paris, Examiner
  • Xavier Delfosse, Astronomer, IPAG UGA, Examiner