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In this Letter we propose a new view on UX Orionis type variability. The ideais based on the earlier proposal by various authors that UXORs arenearly-edge-on disks in which hydrodynamic fluctuations could cause clumps ofdust and gas to cross the line of sight. However, because the standard diskmodels have a flaring geometry, it is mostly the outer regions of the disk thatobscure the star. The time scales for such obscuration events would be too longto match the observed time scales of weeks to months. Recent 2-Dself-consistent models of Herbig Ae/Be protoplanetary disks (Dullemond et al.2002,2003 henceforth D02/DD03), however, have indicated that for Herbig Ae/Bestar disks there exists, in addition to the usual flared disks, also a newclass of disks: those that are fully self-shadowed. Only their puffed-up innerrim (at the dust evaporation radius) is directly irradiated by the star, whilethe disk at larger radius resides in the shadow of the rim. For these disksthere exist inclinations at which the line of sight towards the star skims theupper parts of the puffed-up inner rim, while passing high over the surface ofouter disk regions. Small hydrodynamic fluctuations in the puffed-up inner rimcould then be held responsible for the extinction events seen in UXORs. If thisidea is correct, it makes a prediction for the shape of the SEDs of thesestars. It was shown by D02/DD03 that flared disks have a strong far-IR excessand can be classified as `group I' (in the classification of Meeus et al.2001), while self-shadowed disks have a relatively weak far-IR excess and areclassified as `group II'. Our model therefore predicts that UXORs belong to the`group II' sources. We show that this correlation is indeed found within asample of 86 Herbig Ae/Be stars.Comment: Accepted for publication in ApJ Letters (a few lines added to  original version to accommodate comments of referee

Explaining UX Orionis Star Variability with Self-shadowed Disks