Abstract
We present photometry of the exoplanet host star TrES-3 spanning six occultations (secondary eclipses) of its giant planet. No flux decrements were detected, leading to 99%-confidence upper limits on the planet-to-star flux ratio of 0.00024, 0.0005, and 0.00086 in the i, z, and R bands respectively. The corresponding upper limits on the planet's geometric albedo are 0.30, 0.62, and 1.07. The upper limit in the i band rules out the presence of highly reflective clouds, and is only a factor of 2-3 above the predicted level of thermal radiation from the planet.
Highlights
The detection of reflected light from close-in giant planets is a difficult but worthwhile goal
The difficulty is that the reflected light is a very small fraction of the direct starlight, producing a planet-to-star flux ratio at the opposition of λ = pλ(Rp/a)2, where Rp is the planetary radius, a is the orbital separation, and pλ is the wavelength-dependent geometric albedo
This study has resulted in empirical upper limits on the planetto-star flux ratio, and the geometric albedo, in the wavelength range 0.6–1.0 μm
Summary
The detection of reflected light from close-in giant planets is a difficult but worthwhile goal. Attempts to detect reflected light from close-in giant planets, by Charbonneau et al (1999), Cameron et al (1999, 2002), and Leigh et al (2003a, 2003b), relied on optical spectroscopy Those investigators sought the reflected copies of the stellar spectral lines by combining suitably Doppler-shifted spectra taken over a range of orbital phases. They did not detect the reflected signal and placed upper limits on the geometric albedo in the visual band of ∼0.1–0.5, subject to some ambiguity because of the unknown radius and orbital inclination of the planets they observed.
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