Searching for Brown Dwarf Companions to White Dwarfs
To date, thousands of exoplanets have been discovered and characterised but the high contrast between planets and their host stars makes atmospheric studies difficult. White dwarf–brown dwarf binaries offer unique opportunities to study brown dwarfs and their atmospheres with minimal contamination from the host star when observing in the infrared. Although up to 0.5% of white dwarfs are predicted to have brown dwarf companions, these systems are rare, with only ∼10 known close white dwarf–brown dwarf binaries, and ∼7 such binaries with a wide separation. In this thesis, I present the discovery and characterisation of multiple white dwarf–brown dwarf binary systems. With near-infrared spectroscopy, I find a new wide white dwarf–brown dwarf binary SDSS J2225+0016, which has the third smallest separation for a spatially resolved white dwarf–brown dwarf binary after GD 165AB and PHL 5038AB. I characterise the orbit as well as the brown dwarf and compare this binary to other brown dwarf and exoplanetary systems. I analyse new infrared spectroscopic data of the close, eclipsing white dwarf–brown dwarf binary WD1032+011, extracting the phase-dependent spectra of the brown dwarf. I show the effects of constant irradiation on the atmosphere of the brown dwarf, causing a dayside-nightside temperature contrast and slowing the contraction of the brown dwarf such that its radius is inflated. I examine the candidate white dwarf–brown dwarf binary WD0950+0115 using near-infrared and optical spectroscopy to determine the presence of a companion that causes a radial velocity variation in the Hα and Hβ lines in the atmosphere of the white dwarf. I also present near-infrared spectroscopy of 10 candidate brown dwarf companions to white dwarfs identified via the Backyard Worlds citizen science project. I identify 7 new brown dwarf companions amongst this sample, determining their spectral types, thus adding to the small sample of these rare binaries.
History
Supervisor(s)
Sarah CasewellDate of award
2025-01-05Author affiliation
School of Physics and AstronomyAwarding institution
University of LeicesterQualification level
- Doctoral
Qualification name
- PhD