A GROUND-BASED ALBEDO UPPER LIMIT FOR HD 189733b FROM POLARIMETRY

作者：Wiktorowicz Sloane J^*; Nofi Larissa A; Jontof Hutter Daniel; Kopparla Pushkar; Laughlin Gregory P; Hermis Ninos; Yung Yuk L; Swain Mark R

来源：Astrophysical Journal, 2015, 813(1): 48.

DOI：10.1088/0004-637X/813/1/48

• dust, extinction
• planetary systems
• planets and satellites: atmospheres
• planets and satellites: individual (HD 189733b)
• polarization
• techniques: polarimetric

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 A(g) < 0.40. This value is consistent with the value A(g) = 0.226 +/- 0.091 derived from occultation observations with Hubble Space Telescope STIS, but it is inconsistent with the large A(g) = 0.61 +/- 0.12 albedo reported by Berdyugina et al.

• 出版日期2015-11-1