Vortex Fiber Nulling for Exoplanet Observations

Citation

Echeverri, Daniel (2024) Vortex Fiber Nulling for Exoplanet Observations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/92m5-9p38. https://resolver.caltech.edu/CaltechTHESIS:06032024-080525272

Abstract

As of December 11, 2023, there are just over 5555 confirmed exoplanet detections. Of these exoplanets, only around 200 have been spectroscopically characterized. Spectra are crucial since they provide unique insights into the physical and chemical properties of exoplanets, their atmospheres, and their formation history. Few exoplanet spectra have been obtained because the prevailing spectroscopic techniques, transit spectroscopy and direct imaging, access different physical separations around a star and leave a gap in coverage from about 1 to 10 AU. This gap coincides with the peak of the giant planet occurrence rate such that there is an important population of exoplanets whose spectra cannot be readily obtained with the prevailing techniques. Interferometry can unlock access to these exoplanets and provide spectra for them.

Exoplanet interferometry has seen waves of interest in the past. However new developments, such as the first interferometric detections, have stoked a revived interest. Though VLTI/GRAVITY and other multi-aperture, long-baseline instruments currently dominate the field, there is a push to develop simpler interferometric architectures. Cross-aperture techniques are of particular interest as they can be readily implemented on existing and future direct imaging instruments with few-to-no modifications. Such single-telescope interferometers and nullers can reach well-within the inner working angle of conventional coronagraphs, but require significantly less infrastructure and investment than their long-baseline counterparts.

This thesis presents vortex fiber nulling (VFN), a new cross-aperture technique for detecting and spectroscopically characterizing exoplanets at separations less than one diffraction beamwidth (≾1 λ/D). VFN utilizes the full collecting area of a telescope to efficiently observe within the inner working angle of conventional coronagraphs. The first chapters of this thesis develop the VFN concept and how it can be readily implemented on existing and future instruments. Subsequent chapters present the laboratory demonstrations used to validate the technique and test its limits. Finally, the last chapters cover the design and deployment of a VFN mode to the KPIC instrument at the Keck Telescope. This includes a glimpse into VFN's capabilities with the first direct detection and spectroscopic characterization of three M dwarf companions previously known only from radial velocity and astrometry. This thesis therefore follows the development of VFN from a concept in 2018 to an operating mode with confirmed detections in 2023.

Thesis Files