Color Gradients Detected in the HD 15115 Circumstellar Disk

Abstract

We report HST NICMOS coronagraphic images of the HD 15115 circumstellar disk at 1.1 μm. We find a similar morphology to that seen in the visible and at H band—an edge-on disk that is asymmetric in surface brightness. Several aspects of the 1.1 μm data are different, highlighting the need for multiwavelength images of each circumstellar disk. We find a flattening to the western surface brightness profile at 1.1 μm interior to 2^'' (90 AU) and a warp in the western half of the disk. We measure the surface brightness profiles of the two disk lobes and create a measure of the dust scattering efficiency between 0.55 and 1.65 μm at 1^'', 2^'', and 3^''. At 2^'' the western lobe has a neutral spectrum up to 1.1 μm and a strong absorption or blue spectrum >1.1 μm, while a blue trend is seen in the eastern lobe. At 1^'' the disk has a red F 110W - H color in both lobes.