A Consistent Modeling of Dust Disks Around White Dwarfs

To complete the picture of exoplanet demographics in our universe, understanding populations of planetary systems around evolved stars is essential. White dwarfs represent 97% of stellar remnants in the universe, yet the properties of planetary systems around white dwarfs are not well understood. The primary method of exoplanet detection around white dwarfs is by discovering an infrared (IR) excess consistent with planet emission relative to the white dwarf photosphere. However, dust disks formed from the tidal disruption of a planet or asteroid are known to be common around white dwarfs and may be indistinguishable from the IR emission of planets. In this thesis, we discuss two related projects pertaining to the study of planetary systems around white dwarfs. First, we present our effort to consistently model multiwavelength emission from a sample of dust disks around white dwarfs using the radiative transfer code MCFOST to determine typical white dwarf dust structure and properties. We find that one consistent model can be made to accurately describe disk emission for our sample of 11 targets. However, we find the modeled disk mass and inner radius are not well aligned with theoretical predictions, prompting further study. We find the disk mass to be more massive than is inferred from the accretion of dust onto the white dwarf, and that the inner radius is further out than the nominal radius at which silicate particles are expected to sublimate. Second, we use the disk model assumed in the first part of this analysis to attempt to distinguish between dust and planet emission for a sample of mid-IR excesses associated with white dwarfs observed with JWST. For three white dwarf systems with excesses observed by JWST/MIRI, we are able to largely rule out emission from a warm disk similar to the disks modeled in the first part of this analysis. However, we cannot discriminate between emission from disks located at more distant radii and emission from a planetary mass companion.