Walters, Nikolay;
(2023)
A multi-wavelength observational study of white
dwarfs with anomalous atmospheric signatures.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This thesis explores extrinsic interaction signatures in cool white dwarfs through multicomponent optical and infrared spectra coupled with photometry. The first part of the thesis investigates the mechanism behind Balmer emission lines in isolated white dwarfs, focusing on the unipolar inductor model. The model involves a magnetic interaction between a star and a closely orbiting planet whose motion induces heating in the stellar photosphere. Observations suggest that the emission is intrinsic and rule out star-planet interaction as the cause. The study of the prototype and similar white dwarfs indicates the presence of chromospheres in magnetic white dwarfs, thus forming a new evolutionary class of emitting white dwarfs. The second part of the thesis investigates two possible substellar survivors orbiting white dwarf stars. Infrared and optical spectroscopy of GD 1400 reveals a 70 MJup brown dwarf, while PG 0010+281 may be orbited by a debris disc. An empirical benchmark of 50 MJup is placed on the minimal required mass for a closely orbiting companion to avoid post-main sequence annihilation via stellar evolution. The last part of the thesis examines intrinsic mass loss (wind) from low-mass companions in white dwarf binary systems through the pollution observed in the photospheres of white dwarfs. Mass loss estimates are calculated for M dwarf secondaries and limits on substellar wind accretion are placed based on four white dwarfs with L-type brown dwarf companions, with one case of a highly non-solar abundance ratio detection. The study provides a unique window into brown dwarf activity and upper layer chemical composition through white dwarf atmospheric pollution. Overall, the results described in this thesis offer insight into the properties and evolution of white dwarfs and their companions. This includes the potential presence of chromospheres as well as the survival and behavioural properties of substellar objects during post-main sequence evolution.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | A multi-wavelength observational study of white dwarfs with anomalous atmospheric signatures |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10184595 |
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