Low albedos of hot to ultra-hot Jupiters in the optical to near-infrared transition regime^★,★★

¹ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: mmallonn@aip.de
² Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark

Received: 17 January 2019
Accepted: 20 February 2019

Abstract

The depth of a secondary eclipse contains information of both the thermally emitted light component of a hot Jupiter and the reflected light component. If the day side atmosphere of the planet is assumed to be isothermal, it is possible to disentangle both. In this work, we analyzed 11 eclipse light curves of the hot Jupiter HAT-P-32 b obtained at 0.89 μm in the z′ band. We obtained a null detection for the eclipse depth with state-of-the-art precision, −0.01 ± 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere model is in disagreement to the measured emission spectrum of HAT-P-32 b. We derive an upper limit on the reflected light component, and thus, on the planetary geometric albedo A_g. The 97.5% confidence upper limit is A_g < 0.2. This is the first albedo constraint for HAT-P-32 b, and the first z′ band albedo value for any exoplanet. This finding disfavors the influence of large-sized silicate condensates on the planetary day side. We inferred z′ band geometric albedo limits from published eclipse measurements also for the ultra-hot Jupiters WASP-12 b, WASP-19 b, WASP-103 b, and WASP-121 b, applying the same method. These values consistently point to a low reflectivity in the optical to near-infrared transition regime for hot to ultra-hot Jupiters.