Measuring the vertical height of planet-forming disks from near-infrared scattered light images

Context. High-resolution imaging in scattered light has revealed complex morphologies in circumstellar disks. Measuring their vertical height is key to understanding disk structure, evolution, and the properties of embedded dust. Aims. This thesis aims to develop a robust methodology for fitting elliptical shapes to scattered light images of circumstellar disks in order to extract vertical height profiles across a large and morphologically diverse disk sample. The dataset includes 294 near-infrared, polarimetric images from VLT/SPHERE (Very Large Telescope, Spectro-Polarimetric High-contrast Exoplanet REsearch instrument), covering 186 unique disks. The goal is to identify trends in vertical structure across morphologies and test for correlations with stellar mass, age, and disk dust mass. Using the height profiles, this work also investigates the implications of the constrained height for the masses of potential embedded planets and scattering phase functions. Methods. A structure extraction and ellipse fitting algorithm, building on Ginski et al. (2024), is implemented using edge detection and Gaussian fitting to locate the structure within circumstellar disks. Fitting ellipses to the structure reveals spatial offsets from the centre of the ellipse fit and the star, interpreted as vertical height assuming circular ring geometry. Disk inclination, position angle (PA), and aspect ratio (h/r) are also derived. A denoising convolutional neural network is tested independently as a pre-processing tool. Results. The structure extraction/ellipse fitting algorithm provided successful vertical height measurements for 94 unique disks, revealing variations in height profiles consistent with flared disk geometries. Analysis of the full sample shows that the vertical height profile cannot be confidently described by a single power-law relation. Subdivision of the sample by disk morphology revealed no strong correlations within most categories, with the exception of extended disks (router ≥ 150 au), which exhibited a strong correlation with a single power-law trend. Investigation into underlying disk properties revealed no correlation for its effect to the vertical height structure. Conclusions. This work presents a consistent methodology for measuring the vertical structure of circumstellar disks using ellipse fitting on scattered light images. While global trends in height structure remain moderately correlated, extended disks (router ≥ 150 au) stand out as the only subgroup showing a clear power-law flaring trend. The lack of a strong correlation across other morphologies and with system properties like stellar mass or age suggests that either differing disk morphologies exhibit different vertical height profiles or that another, unidentified factor is affecting the disk flaring.

Publisher

University of Galway

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CC BY-NC-ND

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University of Galway Theses (Research Masters Theses)