Nikolay Walters
I was keen to continue with astrophysics, yet I wanted to center on the more data-driven approach to research questions.
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5 January 2019
Project title:ÌýActive chromospheres in white dwarfsÌý
Research Group: Astrophysics
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I graduated from Ïã¸ÛÁùºÏ²Ê with an Msci in Physics where I achieved first class honours. My masters project was on identification of carbon stars using machine learning techniques. I worked with optical spectra acquired by Sloan Digital Sky Survey (SDSS) and used a decoder from a trained variational autoencoder network to aid a selection of machine learning classifiers. By the end of my project I was keen to continue with astrophysics, yet I wanted to center on the more data-driven approach to research questions. CDT in DIS proved to be a good match, allowing me to both focus on astrophysics while continuing to enrich my understanding of data and its applications in the field.Ìý
Project description:ÌýÌý
My PhD project mostly focuses on a rare class of magnetic white dwarfs. Despite thousands of spectroscopically-identified white dwarfs, when I started my PhD only one isolated and cool star was known to exhibit Balmer emission. Six such systems are now known, suggesting a new class of chromospherically-active white dwarfs. Furthermore, their close grouping on the Hertzsprung-Russell diagram points to a single star evolutionary origin, but with an unknown source of chromospheric heating. The common characteristics of the class are important pieces of the puzzle and include apparent isolation, fast rotation, and magnetism. In my work, I study photometric, spectroscopic, and spectropolarimetric observations of the class prototype, GD 356, where the data point to a temperature inversion similar to that seen in the Sun and cool dwarf stars. Despite the unknown physics, there are several testable predictions if the emission has an intrinsic origin. My current and future work focus on constraining any evolution-activated chromospheric phenomena, with implications for not only this whole class of stellar remnants, but for magnetic stars in general.Ìý
First year group project: NCC Group
Placement:ÌýNCC Group
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