4 research outputs found
A Ground-Based Albedo Upper Limit for HD 189733b from Polarimetry
We present 50 nights of polarimetric observations of HD 189733 in 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 order 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 upper limit to the planet-induced polarization
of the system of 58 ppm in band, which is consistent with a previous upper
limit from the POLISH instrument at the Palomar Observatory 5-m telescope
(Wiktorowicz 2009). A physically-motivated Rayleigh scattering model, which
includes the depolarizing effects of multiple scattering, is used to
conservatively set a upper limit to the geometric albedo of HD
189733b of . This value is consistent with the value derived from occultation observations with HST STIS (Evans et al.
2013), but it is inconsistent with the large albedo
reported by (Berdyugina et al. 2011).Comment: 10 pages, 9 figures, submitted to Ap