Below the Lyman Edge: UV Polarimetry of Quasars

Abstract

Abstract.The Lyman edge at 912A is an important diagnostic region for studying quasi-stellar objects (QSOs). In particular, it reveals a great deal about the physical conditions within the atmospheres of accretion disks, a ubiquitous component of QSO theories. Observations of the Lyman edge regions of QSOs have shown scant evidence for the predicted features -few QSOs show the broad, partial Lyman edges expected to be common according to most theories. The FOS in its polarimetry mode has been instrumental in studying the Lyman edge region in QSOs. One of the most exciting discoveries is that the polarization rises, not at wavelengths longward of the Lyman edge, but at wavelengths well below it! Here we present the status of polarimetry observations at the Lyman edge and discuss their implications to accretions disks.