Imaging & Spectroscopy

CHEOPS Observations Of KELT-20 b/MASCARA-2 b: An Aligned Orbit And Signs Of Variability From A Reflective Dayside

By Keith Cowing
Status Report
November 8, 2023
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CHEOPS Observations Of KELT-20 b/MASCARA-2 b: An Aligned Orbit And Signs Of Variability From A Reflective Dayside
Best-fit occultation depths of individual CHEOPS visits (blue) along with their posteriors on the right. The horizontal solid and dashed lines represent the mean occultation depth of 82.4 ± 5.6 ppm. The panel on the right-side displays the best-fit posterior distribution. The green shaded regions indicate the span of the TESS Sectors 40, 41 and 54 while the brown points indicate sector-wise occultation depth. — astro-ph.EP

Occultations are windows of opportunity to indirectly peek into the dayside atmosphere of exoplanets. High-precision transit events provide information on the spin-orbit alignment of exoplanets around fast-rotating hosts.

We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b as well as the system’s spin-orbit alignment. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with the simultaneous TESS observations. We interpret the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further use the host star’s gravity-darkened nature to measure the system’s obliquity.

We present time-averaged precise occultation depth of 82(6) ppm measured with seven CHEOPS visits and 131(+8/-7) ppm from the analysis of all available TESS photometry. Using these measurements, we precisely constrain the geometric albedo of KELT-20 b to 0.26(0.04) and the brightness temperature of the dayside hemisphere to 2566(+77/-80) K. Assuming Lambertian scattering law, we constrain the Bond albedo to 0.36(+0.04/-0.05) along with a minimal heat transfer to the nightside. Furthermore, using five transit observations we provide stricter constraints of 3.9(1.1) degrees on the sky-projected obliquity of the system.

The aligned orbit of KELT-20 b is in contrast to previous CHEOPS studies that have found strongly inclined orbits for planets orbiting other A-type stars. KELT-20 b’s comparably high planetary geometric albedo corroborates a known trend of strongly irradiated planets being more reflective. Finally, we tentatively detect signs of temporal variability in the occultation depths, which might indicate variable cloud cover advecting onto the planetary dayside.

V. Singh, G. Scandariato, A. M. S. Smith, P. E. Cubillos, M. Lendl, N. Billot, A. Fortier, D. Queloz, S. G. Sousa, Sz. Csizmadia, A. Brandeker, L. Carone, T. G. Wilson, B. Akinsanmi, J. A. Patel, A. Krenn, O. D. S. Demangeon, G. Bruno, I. Pagano, M. J. Hooton, J. Cabrera, N. C. Santos, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, M. Beck, T. Beck, W. Benz, M. Bergomi, A. Bonfanti, X. Bonfils, L. Borsato, C. Broeg, S. Charnoz, A. Collier Cameron, M. B. Davies, M. Deleuil, A. Deline, L. Delrez, B.-O. Demory, D. Ehrenreich, A. Erikson, L. Fossati, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, M. N. Günther, J.-V. Harre, A. Heitzmann, Ch. Helling, S. Hoyer, K. G. Isaak, L. L. Kiss, K. W. F. Lam, J. Laskar, A. Lecavelier des Etangs, D. Magrin, P. F. L. Maxted, H. Mischler, C. Mordasini, V. Nascimbeni, G. Olofsson, R. Ottensamer, E. Pallé, G. Peter, G. Piotto, D. Pollacco, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, S. Salmon, D. Ségransan, A. E. Simon, M. Stalport, M. Steinberger, Gy. M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, J. Venturini, E. Villaver, N. A. Walton, T. Zingales

Comments: 27 pages, 15 figures, Accepted for publication in Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2311.03264 [astro-ph.EP] (or arXiv:2311.03264v1 [astro-ph.EP] for this version)
Submission history
From: Vikash Singh
[v1] Mon, 6 Nov 2023 16:57:17 UTC (5,159 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻