Signposts of Planetary Systems Around Evolved Stars
Recent Spitzer observations have revealed presence of near-IR excesses in spectra of more than thirty white dwarfs with atmospheres enriched in metals. These excesses are naturally interpreted as reprocessing of the stellar emission by compact, optically thick disks of dusty debris. The prevalent idea for the origin of such disks is the tidal disruption of asteroids scattered by massive unseen planets, providing evidence for the existence of the latter around white dwarfs. This circumstellar material has also been proposed as the natural cause of high-Z element pollution of the host white dwarf atmospheres. Accurate measurements of abundances of different elements in these atmospheres give us a unique chance to measure the bulk composition of extrasolar minor objects. I will provide an overview of observations in this rapidly developing area, and will describe recent progress in our understanding of the transfer of high-Z material from the compact circumstellar debris disk onto the white dwarf surface.