Echoes of a decaying planetary system: the gaseous and dusty disks surrounding three white dwarfs

摘要

We have performed a comprehensive ground-based observational program aimed atcharacterizing the circumstellar material orbiting three single white dwarfstars previously known to possess gaseous disks. Near-infrared imagingunambiguously detects excess infrared emission towards Ton 345 and allows us torefine models for the circumstellar dust around all three white dwarf stars. Wefind that each white dwarf hosts gaseous and dusty disks that are roughlyspatially coincident, a result that is consistent with a scenario in whichdusty and gaseous material has its origin in remnant parent bodies of the whitedwarfs' planetary systems. We briefly describe a new model for the gas diskheating mechanism in which the gaseous material behaves like a "Z II" region.In this Z II region, gas primarily composed of metals is photoionized byultraviolet light and cools through optically thick allowed Ca II-lineemission.