A Two-Component Spectral Fitting Analysis of White Dwarf + Companion Systems

We investigate the nature of companions to white dwarfs that display infrared excesses, identified within the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). Using optical spectra from HETDEX and the Sloan Digital Sky Survey (SDSS), combined with near– and mid–infrared photometry from 2MASS and WISE, we perform a two-component fitting analysis with white dwarf templates and spectral companion templates. This approach disentangles the contributions of the white dwarf and its companion, allowing us to constrain the white dwarf's effective temperature and surface gravity while also identifying candidate low-mass stellar and substellar companions. Our results provide new insight into the binary fraction of white dwarfs with cool companions and inform the evolutionary pathways that connect post-main-sequence stellar systems to white dwarf binaries. More broadly, these infrared-excess systems serve as key tracers of late-stage planetary system evolution and the fate of planetary material around evolved stars.