Authors

Sloane J. Wiktorowicz, Gaspard Duchene, James R. Graham, and Paul Kalas

Affiliations

UC Berkeley

Abstract

Using the POLISH instrument on the Lick 3-m, we detect intrinsic, linear polarization from the 49 Cet, 51 Oph, HD 15115, HD 15745, HD 32297, and HD 141569 debris disks in a roughly 300 to 700 nm bandpass. This polarimeter achieves part per million precision on bright targets due to the high-speed modulation and differential nature of its photoelastic modulator. We observe many unpolarized and strongly polarized standards to demonstrate that instrumental systematic effects are negligible. Intrinsic polarization is generated through scattering of photons from the central star by dust grains in optically thin disks. This is corrected for interstellar polarization, which is estimated from nearby stars with similar parallax as the disk. As expected for small particle, single scattering, the polarization PAs of all the above disks except HD 15745 are aligned with the disk minor axes. This suggests that small particle, single scattering environments dominate in these disks. The polarization PA of the HD 15745 disk is oriented 81 +/- 13 degrees from the disk minor axis, and the ratio of polarization degree to optical depth is low (0.0276 +/- 0.0063). While both effects are qualitatively consistent with the observations and forward scattering model presented by Kalas et al. (2007), it is unclear whether the observed degree of polarization can be accounted for in this context. High precision, POLISH observations allow disk-integrated polarization to be detected in disks that are currently undetectable by scattered light imaging, such as those around 49 Cet and 51 Oph. Since the 51 Oph disk is so compact, VLT and Keck interferometry are required to directly detect its near-IR and mid-IR emission, respectively. We directly detect optical, scattered light from this disk, and the disagreement between the polarization PA and the interferometrically derived minor axis PA is only 3.04 +/- 0.77 degrees.