Color Gradients Detected in the HD 15115 Circumstellar Disk

TL;DR

This study presents HST/NICMOS images of the HD 15115 circumstellar disk at 1.1 microns, revealing asymmetries, a warp, and color variations that highlight the complexity of dust scattering properties across wavelengths.

Contribution

First multi-wavelength imaging of HD 15115's disk at 1.1 microns, revealing new structural features and color-dependent scattering behavior.

Findings

Detected a warp in the western disk half.

Observed a neutral spectrum in the western lobe at 2 arcsec.

Found a blue spectrum beyond 1.1 microns in the western lobe.

Abstract

We report HST/NICMOS coronagraphic images of the HD 15115 circumstellar disk at 1.1\micron. 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\micron data are different, highlighting the need for multi-wavelength images of each circumstellar disk. We find a flattening to the western surface brightness profile at 1.1\micron interior to 2\arcsec (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 0.55-1.65\micron at 1\arcsec, 2\arcsec, and 3\arcsec. At 2\arcsec the western lobe has a neutral spectrum up to 1.1\micron and a strong absorption or blue spectrum $>$1.1\micron, while a blue trend is seen in the eastern lobe. At 1\arcsec the disk has a red F110W-H color in both lobes.