Modeling of accretion disks originating from disrupted planetary bodies around white dwarfs
speaker: Ayaka Okuya
Abstract:
From a quarter to a half of WDs have rock-forming elements in their atmospheres, and some of them show infrared excess from their circumstellar dusty disks. These are thought to be originated from the tidally disrupted minor planets. Therefore, the metals in the WD atmospheres would enable us to directly measure the elemental composition of exoplanetary bodies with unprecedented precision. Moreover, the dynamical arguments based on the delivery rate of minor planets to the Roche limit could provide unique insights into the planetary system architecture orbiting around WDs.
In this study, as a first step to establishing the framework that can derive such information from observations, we develop the first accretion disk model that solves the coupled evolution of multiple materials. We find that the disks produced by the disrupted rocky bodies cannot reproduce the observed high accretion rate due to the rapid re-condensation of diffused-out vapor just outside the silicate sublimation line. In the case of icy body accretion, the volatile vapor can enhance the silicate accretion rate through gas drag to successfully achieve the observed high accretion rate. We find that, however, a high silicate accretion rate is always accompanied by a comparably high volatile accretion rate, resulting in the volatile-rich photospheric composition. This is inconsistent with the observed photospheric composition. No solution that reproduces observations implies that the existing disk models miss some physical processes and/or that the current data interpretation method might have some problems. I will finally discuss the future direction of this study.