PhD defence by Mona El Morsy

“Development of a prototype instrument for the characterisation of young giant exoplanets”

he defence will be held in English, and it will be possible to attend remotely through zoom at the following link:
https://univ-amu-fr.zoom.us/j/83713561721?pwd=RzA2dklwZ0x4NXZhZVBxSHVoM3cvZz09

Please find below the PhD thesis abstract and the jury members.

Abstract:

On large ground-based telescopes, the combination of extreme adaptive optics and coronagraphy with high-dispersion spectroscopy, referred to as high-dispersion coronagraphy (HDC), emerged as a powerful technique for the direct characterisation of giant exoplanets. The high spectral resolution of this method brings a major gain in terms of accessible spectral features, and enables a better separation of the stellar and planetary signals. The instrument HiRISE aims to exploit these anticipated success factors. It bases its observing strategy on the use of a few science fibres: one is dedicated to sampling the planet’s signal, while the others sample the residual starlight in the speckle field. For precision and stability purposes, single-mode fibres (SMF) are optimal for feeding light into spectrographs, as in the case of HiRISE. SMFs are used in the focal plane of telescopes for their spatial filtering effect. However, efficiently coupling a PSF into a SMF is inherently challenging due to their intrinsic properties described throughout this thesis.

One of the challenges of HiRISE resides in blindly centring the planet’s signal of a previously known exoplanet detected by SPHERE into a SMF. The Fibre Injection Module (FIM) part plays a critical role since it will pick up the planet’s PSF in SPHERE and inject it into a SMF located in the fibre bundle to feed the spectrograph. To maximise the coupling efficiency, the planet’s PSF must be positioned with an accuracy better than 0.1 lambda/D (4 mas in the H band for SPHERE) to minimise light losses. Therefore, defining the best possible strategy for HiRISE to centre the planet’s PSF on a SMF is essential.

In the framework of the thesis, I defined, implemented and tested three strategies for centring a planet PSF in an SMF. I compared their centring accuracy using an upgraded high contrast imaging testbed (MITHiC) setup, which emulates the instrument setup used in HiRISE.
The results demonstrate that reaching a specification accuracy of 0.1 lambda/D is challenging regardless of the chosen centring strategy. It requires a high level of accuracy at every step of the centring procedure, which can be reached with very stable instruments. I studied the contributors to the centring error and proposed quantifying the most impactful terms. The goal of my work was to analyse the difference between the work done on MITHiC and its implementation on HiRISE, and to extrapolate to the challenges we will meet on sky. Some validation regarding the best centring strategy for HiRISE will emerge from the AIT phase, but the final decision regarding the centring strategy will be taken after the on-sky tests.

It is likely that HDC will continue using fibre-fed spectrographs in the foreseeable future. My study, therefore, prepares the ground for instruments like RISTRETTO/VLT, PCS/ELT, MODHIS/TMT — or post-JWST flagship missions.

Jury members:

Referees:

Dimitri Mawet
Professor of Astronomy; Jet Propulsion Laboratory/California
Institute of Technology, USA

Claire Moutou
Directrice de Recherche CNRS; Institut de Recherche en Astrophysique
et Planétologie (IRAP), France

Examiners:

Elsa Huby
Astronome-adjointe CNAP; Laboratoire d’Etudes Spatiales et
d’Instrumentation en Astrophysique (LESIA)/ Observatoire de
Paris/PSL, France

Alexis Carlotti
Astronome-adjoint CNAP; Institut de Planétologie et d’Astrophysique
de Grenoble (IPAG), France

President:

Jean-Luc Beuzit
Directeur de Recherche CNRS; Laboratoire d’Astrophysique de Marseille (LAM),
France

PhD advisor:

Arthur Vigan
Chargé de recherche CNRS (HDR);  Laboratoire d’Astrophysique de
Marseille (LAM), France