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CHEOPS geometric albedo of the hot Jupiter HD 209458 b

Maxted

Authors



Abstract

We report the detection of the secondary eclipse of the hot Jupiter HD 209458 b in optical/visible light using the CHEOPS space telescope. Our measurement of 20.4(-3.3)(+3.2) parts per million translates into a geometric albedo of A(g) = 0.096 +/- 0.016. The previously estimated dayside temperature of about 1500 K implies that our geometric albedo measurement consists predominantly of reflected starlight and is largely uncontaminated by thermal emission. This makes the present result one of the most robust measurements of A(g) for any exoplanet. Our calculations of the bandpassintegrated geometric albedo demonstrate that the measured value of A(g) is consistent with a cloud-free atmosphere, where starlight is reflected via Rayleigh scattering by hydrogen molecules, and the water and sodium abundances are consistent with stellar metallicity. We predict that the bandpass-integrated TESS geometric albedo is too faint to detect and that a phase curve of HD 209458 b observed by CHEOPS would have a distinct shape associated with Rayleigh scattering if the atmosphere is indeed cloud free.

Acceptance Date Feb 16, 2022
Publication Date Mar 2, 2022
Journal Astronomy & Astrophysics
Print ISSN 0004-6361
Publisher EDP Sciences
Pages L4 - L4
DOI https://doi.org/10.1051/0004-6361/202243082
Keywords techniques: photometric / planetary systems / planets and satellites: atmospheres / planets and satellites: individual: HD 209458 b
Publisher URL https://www.aanda.org/articles/aa/full_html/2022/03/aa43082-22/aa43082-22.html