CHEOPS geometric albedo of the hot Jupiter HD 209458 b

A. Brandeker , K. Heng , M. Lendl , J. A. Patel , B. M. Morris , C. Broeg , P. Guterman (1) , M. Beck , P. F. L. Maxted , O. Demangeon , L. Delrez , B. -O. Demory , D. Kitzmann , N. C. Santos , V. Singh , Y. Alibert , R. Alonso , G. Anglada , T. Bárczy , D. Barrado y Navascues , S. C. C. Barros , W. Baumjohann , T. Beck , W. Benz , N. Billot , X. Bonfils (2) , G. Bruno , J. Cabrera , S. Charnoz (3) , A. Collier Cameron , C. Corral van Damme , Sz. Csizmadia , M. B. Davies , M. Deleuil (1) , A. Deline , D. Ehrenreich , A. Erikson , J. Farinato , A. Fortier , L. Fossati , M. Fridlund , D. Gandolfi , M. Gillon , M. Güdel , S. Hoyer (1) , K. G. Isaak , L. Kiss , J. Laskar (4) , A. Lecavelier Des Etangs (5) , C. Lovis , A. Luntzer , D. Magrin , V. Nascimbeni , G. Olofsson , R. Ottensamer , I. Pagano , E. Pallé , G. Peter , G. Piotto , D. Pollacco , D. Queloz , R. Ragazzoni , N. Rando , H. Rauer , I. Ribas , G. Scandariato , D. Ségransan , A. E. Simon , A. M. S. Smith , S. G. Sousa , M. Steller , G. M. Szabó , N. Thomas , S. Udry , V. van Grootel , N. Walton , D. Wolter

1 LAM - Laboratoire d'Astrophysique de Marseille
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
3 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
4 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
5 IAP - Institut d'Astrophysique de Paris

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 bandpass-integrated 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.

The raw and detrended photometric time-series data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/659/L4

Keywords: techniques: photometric; planetary systems; planets and satellites: atmospheres; planets and satellites: individual: HD 209458 b

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

A. Brandeker, K. Heng, M. Lendl, J. A. Patel, B. M. Morris, et al.. CHEOPS geometric albedo of the hot Jupiter HD 209458 b. Astronomy and Astrophysics - A&A, 2022, 659, ⟨10.1051/0004-6361/202243082⟩. ⟨insu-03705369⟩