The Geometry of the G29-38 White Dwarf Dust Disk from Radiative Transfer Modeling

Many white dwarfs host disks of dust produced by disintegrating planetesimals and revealed by infrared excesses. The disk around G29-38 was the first to be discovered and is now well-observed, yet we lack a cohesive picture of its geometry and dust properties. Here we model the G29-38 disk for the first time using radiative transfer calculations that account for radial and vertical temperature and optical depth gradients. We arrive at a set of models that can match the available infrared measurements well, although they overpredict the width of the 10 mu m silicate feature. The resulting set of models has a disk inner edge located at 92-100 R (WD) (where R (WD) is the white dwarf radius). This is farther from the star than inferred by previous modeling efforts due to the presence of a directly illuminated front edge to the disk. The radial width of the disk is narrow (<= 10 R (WD)); such a feature could be explained by inefficient spreading or the proximity of the tidal disruption radius to the sublimation radius. The models have a half-opening angle of >= 1.degrees 4. Such structure would be in strong contradiction with the commonly employed flat-disk model analogous to the rings of Saturn, and in line with the vertical structure of main-sequence debris disks. Our results are consistent with the idea that disks are collisionally active and continuously fed with new material, rather than evolving passively after the disintegration of a single planetesimal.

Automated summary

This study models the G29-38 disk using radiative transfer calculations for the first time and presents a set of models that explain the dust properties and structure of the disk. The results suggest that the inner edge of the disk is farther from the star than previously thought and provide explanations for the narrow radial width and vertical half-opening angle of the disk.