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CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective day side

Singh, V. ; Davies, M.B. LU and Zingales, T. (2024) In Astronomy and Astrophysics 683.
Abstract
Context. 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. Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system. Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star's... (More)
Context. 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. Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system. Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star's gravity-darkened nature to measure the system's obliquity. Results. We present a time-averaged precise occultation depth of 82 ± 6 ppm measured with seven CHEOPS visits and 131-7+8 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 2566-80+77 K. Assuming Lambertian scattering law, we constrain the Bond albedo to 0.36-0.05+0.04 along with a minimal heat transfer to the night side (Ïμ = 0.14-0.10+0.13). Furthermore, using five transit observations we provide stricter constraints of 3 9 ± 1 1 deg on the sky-projected obliquity of the system. Conclusions. 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. The comparably high planetary geometric albedo of KELT-20 b 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 day side. © The Author(s) 2024. (Less)
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Planets and satellites: atmospheres, Planets and satellites: gaseous planets, Planets and satellites: individual: KELT-20 b, Planets and satellites: individual: MASCARA-2 b, Techniques: photometric, Exoplanets, Geometry, Heat transfer, Photometry, Satellites, Solar radiation, Stars, Exo-planets, Geometric albedos, Planet and satellite: gaseous planet, Planet and satellite: individual: KELT-20 b, Planet and satellite: individual: MASCARA-2 b, Planets and satellites, Planets and satellites: individual, Orbits
in
Astronomy and Astrophysics
volume
683
article number
A1
publisher
EDP Sciences
external identifiers
  • scopus:85186624090
ISSN
0004-6361
DOI
10.1051/0004-6361/202347533
language
English
LU publication?
yes
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Number of authors = 90 EID = 85186624090 Article no = A1 Affiliation = Singh V., Inaf, Osservatorio Astrofisico di Catania, Via S. Sofia 78, Catania, 95123, Italy Affiliation = Walton N.A., Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, United Kingdom Affiliation = Zingales T., Inaf, Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, Padova, 35122, Italy, Dipartimento di Fisica e Astronomia "Galileo Galilei", Università Degli Studi di Padova, Vicolo dell'Osservatorio 3, Padova, 35122, Italy
id
92d966ba-0ff7-4459-9f5d-f69e7c546961
date added to LUP
2024-03-28 14:27:15
date last changed
2024-03-28 14:28:43
@article{92d966ba-0ff7-4459-9f5d-f69e7c546961,
  abstract     = {{Context. 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. Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system. Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star's gravity-darkened nature to measure the system's obliquity. Results. We present a time-averaged precise occultation depth of 82 ± 6 ppm measured with seven CHEOPS visits and 131-7+8 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 2566-80+77 K. Assuming Lambertian scattering law, we constrain the Bond albedo to 0.36-0.05+0.04 along with a minimal heat transfer to the night side (Ïμ = 0.14-0.10+0.13). Furthermore, using five transit observations we provide stricter constraints of 3 9 ± 1 1 deg on the sky-projected obliquity of the system. Conclusions. 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. The comparably high planetary geometric albedo of KELT-20 b 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 day side.  © The Author(s) 2024.}},
  author       = {{Singh, V. and Davies, M.B. and Zingales, T.}},
  issn         = {{0004-6361}},
  keywords     = {{Planets and satellites: atmospheres; Planets and satellites: gaseous planets; Planets and satellites: individual: KELT-20 b; Planets and satellites: individual: MASCARA-2 b; Techniques: photometric; Exoplanets; Geometry; Heat transfer; Photometry; Satellites; Solar radiation; Stars; Exo-planets; Geometric albedos; Planet and satellite: gaseous planet; Planet and satellite: individual: KELT-20 b; Planet and satellite: individual: MASCARA-2 b; Planets and satellites; Planets and satellites: individual; Orbits}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective day side}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202347533}},
  doi          = {{10.1051/0004-6361/202347533}},
  volume       = {{683}},
  year         = {{2024}},
}