A Ground-Based Albedo Upper Limit for HD 189733b From Polarimetry (the Astrophysical Journal, 2015)

• Yuk Yung

Full Citation:
Wiktorowicz, S. J., Nofi, L. A., Jontof-Hutter, D., Kopparla, P., Laughlin, G. P., Hermis, N., Yung, Y. L., & Swain, M. R. (2015). A Ground-based Albedo Upper Limit for HD 189733b From Polarimetry. The Astrophysical Journal, 813(1), 48. Https://doi.org/10.1088/0004-637x/813/1/48

Abstract:
We present 50 nights of polarimetric observations of HD 189733 in the B band using the POLISH2 aperture-integrated polarimeter at the Lick Observatory Shane 3-m telescope. This instrument, commissioned in 2011, is designed to search for Rayleigh scattering from short-period exoplanets due to the polarized nature of scattered light. Since these planets are spatially unresolvable from their host stars, the relative contribution of the planet-to-total system polarization is expected to vary with an amplitude of the order of 10 parts per million (ppm) over the course of the orbit. Non-zero and also variable at the 10 ppm level, the inherent polarization of the Lick 3-m telescope limits the accuracy of our measurements and currently inhibits conclusive detection of scattered light from this exoplanet. However, the amplitude of observed variability conservatively sets a 99.7% confidence upper limit to the planet-induced polarization of the system of 60 ppm in the B band, which is consistent with a previous upper limit from the POLISH instrument at the Palomar Observatory 5-m telescope. A physically motivated Rayleigh scattering model, which includes the depolarizing effects of multiple scattering, is used to conservatively set a 99.7% confidence upper limit to the geometric albedo of HD 189733b of Ag < 0.40. This value is consistent with the value ${A}_{g}=0.226\pm 0.091$ derived from occultation observations with Hubble Space Telescope STIS, but it is inconsistent with the large ${A}_{g}=0.61\pm 0.12$ albedo reported by Berdyugina et al.

URL:
https://iopscience.iop.org/article/10.1088/0004-637X/813/1/48/meta

VPL Research Tasks:
Task E: The Observer