THE DEEP BLUE COLOR OF HD 189733b: ALBEDO MEASUREMENTS WITH <i>HUBBLE SPACE TELESCOPE</i> /SPACE TELESCOPE IMAGING SPECTROGRAPH AT VISIBLE WAVELENGTHS

Abstract

We present a secondary eclipse observation for the hot Jupiter HD189733b\nacross the wavelength range 290-570nm made using the Space Telescope Imaging\nSpectrograph on the Hubble Space Telescope. We measure geometric albedos of Ag\n= 0.40 \\pm 0.12 across 290-450nm and Ag &lt; 0.12 across 450-570nm at 1-sigma\nconfidence. The albedo decrease toward longer wavelengths is also apparent when\nusing six wavelength bins over the same wavelength range. This can be\ninterpreted as evidence for optically thick reflective clouds on the dayside\nhemisphere with sodium absorption suppressing the scattered light signal beyond\n~450nm. Our best-fit albedo values imply that HD189733b would appear a deep\nblue color at visible wavelengths.\n