White Dwarfs with Infrared Excess in the HET Dark Energy Experiment

Abstract

White dwarfs with infrared excess emission provide a window into the late stages of stellar evolution and the dynamics of circumstellar environments. Using data from the Hobby–Eberly Telescope Dark Energy Experiment, we characterized 30 white dwarfs exhibiting infrared excess, including 29 DA and 1 DB stars. While an infrared excess can arise from dusty disks or cool (sub)stellar companions, our sample is limited to stellar companions, due to our selection based on SDSS photometry, which is sensitive to excess emission at wavelengths λ < 1 μm. Our sample contains 22 newly identified excess sources not previously reported in the literature. Spectroscopic observations are available for 10 sources via SDSS, of which only 8 have prior spectroscopic classifications in the literature. In this paper, we present the determination of the effective temperature and surface gravity of these white dwarfs. We used the Balmer line profiles to compare with current atmospheric models in order to determine the photospheric parameters of the white dwarfs, minimizing contamination introduced by the infrared source. We used photometric data from the SDSS and the Gaia mission to resolve the degeneracies between hot and cold solutions from spectroscopy, constraining the photospheric parameters. These results help refine our understanding of white dwarf evolution in binary systems, focusing on stellar companions that cause the infrared excess. This study contributes to identifying systems with potential substellar companions or unresolved stellar partners, adding to the growing effort to map out the fate of planetary systems after their host stars evolve beyond the main sequence.