AA Tauri’s sudden and long-lasting deepening: enhanced extinction by its circumstellar disk

Abstract

Context. AA Tau has been monitored for more than 20 years since 1987 and exhibited a nearly constant brightness level of V = 12.5 mag. We report here that in 2011 it suddenly faded, becoming 2 mag fainter in the V-band, and has remained in this deep state since then.