The Warped Circumstellar Disk of HD 100546

We propose that the two armed spiral features seen in visible Hubble SpaceTelescope images of scattered light in HD100546's circumstellar disk are causedby the illumination of a warped outer disk. A tilt of 6-15 degrees from thesymmetry plane can cause the observed surface brightness variations providingthe disk is very twisted (highly warped) at radii greater than 200 AU where thespiral features are seen. Dust lanes are due in part to shadowing in theequatorial plane from the inner disk within a radius of 100 AU. HD100546'souter disk, if viewed edge-on, would appear similar to that of Beta Pictorus. Adisk initially misaligned with a planetary system, becomes warped due toprecession induced by planetesimal bodies and planets. However, the twistednessof HD100546's disk cannot be explained by precession during the lifetime of thesystem induced by a single Jovian mass planet within the clearing at ~13 AU.One possible explanation for the corrugated disk is that precession was inducedby massive of bodies embedded in the disk at larger radius. This would requireapproximately a Jupiter mass of bodies well outside the central clearing at 13AU and within the location of the spiral features or at radii approximatelybetween 50-200 AU.Comment: submitted to Ap