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

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. Palle; 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

doi:10.1051/0004-6361/202347533

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

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. HootonJ. 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. Palle, 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

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

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 (ε = 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.

Original language	English
Article number	A1
Number of pages	25
Journal	Astronomy & Astrophysics
Volume	683
Early online date	29 Feb 2024
DOIs	https://doi.org/10.1051/0004-6361/202347533
Publication status	Published - Mar 2024

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

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Singh_2024_AandA_CHEOPS-observations-KELT-20b-MASCARA-2b_CC
Copyright © The Authors 2024. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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AO2 - Professor Andrew Cameron: Project AO2 - Andrew Cameron
Cameron, A. C. (PI)
Science & Technology Facilities Council
1/04/21 → 31/03/24
Project: Standard
Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021
Jardine, M. M. (PI), Bonnell, I. A. (CoI), Cameron, A. C. (CoI), Cyganowski, C. J. (CoI), Dominik, M. (CoI), Helling, C. (CoI), Horne, K. D. (CoI), Scholz, A. (CoI), Tojeiro, R. (CoI), Weijmans, A.-M. (CoI), Wild, V. (CoI), Woitke, P. (CoI), Wood, K. (CoI) & Zhao, H. (CoI)
1/04/18 → 31/03/22
Project: Standard
Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation
Cameron, A. C. (PI)
Science & Technology Facilities Council
1/08/17 → 31/12/22
Project: Standard

KELT-20b/MASCARA-2b CHEOPS light curve
Singh, V. (Creator), Scandariato, G. (Creator), Smith, A. M. S. (Creator), Cubillos, P. E. (Creator), Lendl, M. (Creator), Billot, N. (Creator), Fortier, A. (Creator), Queloz, D. (Creator), Sousa, S. G. (Creator), Sz, C. (Creator), Brandeker, A. (Creator), Carone, L. (Creator), Wilson, T. G. (Creator), Akinsanmi, B. (Creator), Patel, J. A. (Creator), Krenn, A. (Creator), Demangeon, O. D. S. (Creator), Bruno, G. (Creator), Pagano, I. (Creator), Hooton, M. J. (Creator), Cabrera, J. (Creator), Santos, N. C. (Creator), Alibert, Y. (Creator), Alonso, R. (Creator), Asquier, J. (Creator), Barczy, T. (Creator), Barrado Navascues, D. (Creator), Barros, S. C. C. (Creator), Baumjohann, W. (Creator), Beck, M. (Creator), Beck, T. (Creator), Benz, W. (Creator), Bergomi, M. (Creator), Bonfanti, A. (Creator), Bonfils, X. (Creator), Borsato, L. (Creator), Broeg, C. (Creator), Charnoz, S. (Creator), Collier Cameron, A. (Creator), Davies, M. B. (Creator), Deleuil, M. (Creator), Deline, A. (Creator), Delrez, L. (Creator), Demory, B.-O. (Creator), Ehrenreich, D. (Creator), Erikson, A. (Creator), Fossati, L. (Creator), Fridlund, M. (Creator), Gandolfi, D. (Creator), Gillon, M. (Creator), Guedel, M. (Creator), Guenther, M. N. (Creator), Harre, J.-V. (Creator), Heitzmann, A. (Creator), Helling, C. (Creator), Hoyer, S. (Creator), Isaak, K. G. (Creator), Kiss, L. L. (Creator), K.W.F., L. (Creator), Laskar, J. (Creator), Lecavelier Des Etangs, A. (Creator), Magrin, D. (Creator), Maxted, P. F. L. (Creator), Mischler, H. (Creator), Mordasini, C. (Creator), Nascimbeni, V. (Creator), Olofsson, G. (Creator), Ottensamer, R. (Creator), Palle, E. (Creator), Peter, G. (Creator), Piotto, G. (Creator), Pollacco, D. (Creator), Ragazzoni, R. (Creator), Rando, N. (Creator), Rauer, H. (Creator), Ribas, I. (Creator), Salmon, S. (Creator), Segransan, D. (Creator), Simon, A. E. (Creator), Stalport, M. (Creator), Steinberger, M. (Creator), GyM., S. (Creator), Thomas, N. (Creator), Udry, S. (Creator), Ulmer, B. (Creator), Van Grootel, V. (Creator), Venturini, J. (Creator), Villaver, E. (Creator), Walton, N. A. (Creator) & Zingales, T. (Creator), Centre de Donnees Strasbourg (CDS), 2024
DOI: 10.26093/cds/vizier.36830001
Dataset

Cite this

Singh, V., Scandariato, G., Smith, A. M. S., Cubillos, P. E., Lendl, M., Billot, N., Fortier, A., Queloz, D., Sousa, S. G., Csizmadia, S., Brandeker, A., Carone, L., Wilson, T. G., Akinsanmi, B., Patel, J. A., Krenn, A., Demangeon, O. D. S., Bruno, G., Pagano, I., ... Zingales, T. (2024). CHEOPS observations of KELT-20 b/MASCARA-2 b: an aligned orbit and signs of variability from a reflective day side. Astronomy & Astrophysics, 683, Article A1. https://doi.org/10.1051/0004-6361/202347533

@article{2c562094ab624bdf81eb28951eb57fa0,

title = "CHEOPS observations of KELT-20 b/MASCARA-2 b: an aligned orbit and signs of variability from a reflective day side",

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 (ε = 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.",

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",

author = "V. Singh and G. Scandariato and Smith, {A. M. S.} and Cubillos, {P. E.} and M. Lendl and N. Billot and A. Fortier and D. Queloz and Sousa, {S. G.} and Sz Csizmadia and A. Brandeker and L. Carone and Wilson, {T. G.} and B. Akinsanmi and Patel, {J. A.} and A. Krenn and Demangeon, {O. D. S.} and G. Bruno and I. Pagano and Hooton, {M. J.} and J. Cabrera and Santos, {N. C.} and Y. Alibert and R. Alonso and J. Asquier and T. B{\'a}rczy and {Barrado Navascues}, D. and Barros, {S. C. C.} and W. Baumjohann and M. Beck and T. Beck and W. Benz and M. Bergomi and A. Bonfanti and X. Bonfils and L. Borsato and C. Broeg and S. Charnoz and Cameron, {A. Collier} and Davies, {M. B.} and M. Deleuil and A. Deline and L. Delrez and Demory, {B. -O.} and D. Ehrenreich and A. Erikson and L. Fossati and M. Fridlund and D. Gandolfi and M. Gillon and M. G{\"u}del and G{\"u}nther, {M. N.} and Harre, {J. V.} and A. Heitzmann and Ch Helling and S. Hoyer and Isaak, {K. G.} and Kiss, {L. L.} and Lam, {K. W. F.} and J. Laskar and {Lecavelier des Etangs}, A. and D. Magrin and Maxted, {P. F. L.} and H. Mischler and C. Mordasini and V. Nascimbeni and G. Olofsson and R. Ottensamer and E. Palle and G. Peter and G. Piotto and D. Pollacco and R. Ragazzoni and N. Rando and H. Rauer and I. Ribas and S. Salmon and D. S{\'e}gransan and Simon, {A. E.} and M. Stalport and M. Steinberger and Szab{\'o}, {Gy M.} and N. Thomas and S. Udry and B. Ulmer and {Van Grootel}, V. and J. Venturini and E. Villaver and Walton, {N. A.} and T. Zingales",

note = "Funding: V.Si., G.Sc., G.Br., I.Pa., L.Bo., V.Na., G.Pi., R.Ra., and T.Zi. acknowledge support from CHEOPS ASI-INAF agreement no. 2019-29-HH.0. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, program J4595-N. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). S.G.S. acknowledges support from FCT through FCT contract no. CEECIND/00826/2018 and POPH/FSE (EC). A.Br. was supported by the SNSA. L.Ca. and C.He. acknowledge support from the European Union H2020- MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON). T.Wi. acknowledges support from the UKSA and the University of Warwick. This work was supported by FCT – Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia through national funds and by FEDER through COMPETE2020 through the research grants UIDB/04434/2020, UIDP/04434/2020, 2022.06962.PTDC. O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. N.C.Sa. acknowledges funding by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Y.Al. acknowledges support from the Swiss National Science Foundation (SNSF) under grant 200020_192038. R.Al., D.Ba., E.Pa., and I.Ri. acknowledge financial support from the Agencia Estatal de Investigaci{\'o}n of the Ministerio de Ciencia e Innovaci{\'o}n MCIN/AEI/10.13039/501100011033 and the ERDF “A way of making Europe” through projects PID2019-107061GB-C61, PID2019-107061GB-C66, PID2021-125627OB-C31, and PID2021-125627OB-C32, from the Centre of Excellence “Severo Ochoa” award to the Instituto de Astrof{\'i}sica de Canarias (CEX2019-000920-S), from the Centre of Excellence “Mar{\'i}a de Maeztu” award to the Institut de Ci{\`e}ncies de l{\textquoteright}Espai (CEX2020-001058-M), and from the Generalitat de Catalunya/CERCA programme. S.C.C.B. acknowledges support from FCT through FCT contracts nr. IF/01312/2014/CP1215/CT0004. X.B., S.C., D.G., M.F. and J.L. acknowledge their role as ESA-appointed CHEOPS science team members. C.Br. and A.Si. acknowledge support from the Swiss Space Office through the ESA PRODEX program. A.C.C. acknowledges support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. This project was supported by the CNES. The Belgian participation to CHEOPS has been supported by the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Program, and by the University of Li{\`e}ge through an ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. L.D. is an F.R.S.-FNRS Postdoctoral Researcher. B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. This project has received funding from the European Research Council (ERC) under the European Union{\textquoteright}s Horizon 2020 research and innovation programme (project FOUR ACES. grant agreement no. 724427). It has also been carried out in the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). D.E. acknowledges financial support from the Swiss National Science Foundation for project 200021_200726. M.F. and C.M.P. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). D.G. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseousor rocky? Unveiling the nature of small worlds”. M.G. is an F.R.S.-FNRS Senior Research Associate. M.N.G. is the ESA CHEOPS Project Scientist and Mission Representative, and as such also responsible for the Guest Observers (GO) Programme. M.N.G. does not relay proprietary information between the GO and Guaranteed Time Observation (GTO) Programmes, and does not decide on the definition and target selection of the GTO Programme. S.H. gratefully acknowledges CNES funding through the grant 837319. K.G.I. is the ESA CHEOPS Project Scientist and is responsible for the ESA CHEOPS Guest Observers Programme. She does not participate in, or contribute to, the definition of the Guaranteed Time Programme of the CHEOPS mission through which observations described in this paper have been taken, nor to any aspect of target selection for the programme. K.W.F.L. was supported by Deutsche Forschungsgemeinschaft grants RA714/14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. This work was granted access to the HPC resources of MesoPSL financed by the Region Ile de France and the project Equip@Meso (reference ANR-10-EQPX29-01) of the programme Investissements d{\textquoteright}Avenir supervised by the Agence Nationale pour la Recherche. P.M. acknowledges support from STFC research grant number ST/M001040/1. Gy.M.Sz. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Experiment Agreement No. 4000137122, the Lend{\"u}let LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. V.V.G. is an F.R.S-FNRS Research Associate. N.A.W. acknowledges UKSA grant ST/R004838/1. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA{\textquoteright}s Science Mission Directorate.",

year = "2024",

month = mar,

doi = "10.1051/0004-6361/202347533",

language = "English",

volume = "683",

journal = "Astronomy & Astrophysics",

issn = "0004-6361",

publisher = "EDP SCIENCES S A",

}

Singh, V, Scandariato, G, Smith, AMS, Cubillos, PE, Lendl, M, Billot, N, Fortier, A, Queloz, D, Sousa, SG, Csizmadia, S, Brandeker, A, Carone, L, Wilson, TG, Akinsanmi, B, Patel, JA, Krenn, A, Demangeon, ODS, Bruno, G, Pagano, I, Hooton, MJ, Cabrera, J, Santos, NC, Alibert, Y, Alonso, R, Asquier, J, Bárczy, T, Barrado Navascues, D, Barros, SCC, Baumjohann, W, Beck, M, Beck, T, Benz, W, Bergomi, M, Bonfanti, A, Bonfils, X, Borsato, L, Broeg, C, Charnoz, S, Cameron, AC, Davies, MB, Deleuil, M, Deline, A, Delrez, L, Demory, B-O, Ehrenreich, D, Erikson, A, Fossati, L, Fridlund, M, Gandolfi, D, Gillon, M, Güdel, M, Günther, MN, Harre, JV, Heitzmann, A, Helling, C, Hoyer, S, Isaak, KG, Kiss, LL, Lam, KWF, Laskar, J, Lecavelier des Etangs, A, Magrin, D, Maxted, PFL, Mischler, H, Mordasini, C, Nascimbeni, V, Olofsson, G, Ottensamer, R, Palle, E, Peter, G, Piotto, G, Pollacco, D, Ragazzoni, R, Rando, N, Rauer, H, Ribas, I, Salmon, S, Ségransan, D, Simon, AE, Stalport, M, Steinberger, M, Szabó, GM, Thomas, N, Udry, S, Ulmer, B, Van Grootel, V, Venturini, J, Villaver, E, Walton, NA & Zingales, T 2024, 'CHEOPS observations of KELT-20 b/MASCARA-2 b: an aligned orbit and signs of variability from a reflective day side', Astronomy & Astrophysics, vol. 683, A1. https://doi.org/10.1051/0004-6361/202347533

TY - JOUR

T1 - CHEOPS observations of KELT-20 b/MASCARA-2 b

T2 - an aligned orbit and signs of variability from a reflective day side

AU - Singh, V.

AU - Scandariato, G.

AU - Smith, A. M. S.

AU - Cubillos, P. E.

AU - Lendl, M.

AU - Billot, N.

AU - Fortier, A.

AU - Queloz, D.

AU - Sousa, S. G.

AU - Csizmadia, Sz

AU - Brandeker, A.

AU - Carone, L.

AU - Wilson, T. G.

AU - Akinsanmi, B.

AU - Patel, J. A.

AU - Krenn, A.

AU - Demangeon, O. D. S.

AU - Bruno, G.

AU - Pagano, I.

AU - Hooton, M. J.

AU - Cabrera, J.

AU - Santos, N. C.

AU - Alibert, Y.

AU - Alonso, R.

AU - Asquier, J.

AU - Bárczy, T.

AU - Barrado Navascues, D.

AU - Barros, S. C. C.

AU - Baumjohann, W.

AU - Beck, M.

AU - Beck, T.

AU - Benz, W.

AU - Bergomi, M.

AU - Bonfanti, A.

AU - Bonfils, X.

AU - Borsato, L.

AU - Broeg, C.

AU - Charnoz, S.

AU - Cameron, A. Collier

AU - Davies, M. B.

AU - Deleuil, M.

AU - Deline, A.

AU - Delrez, L.

AU - Demory, B. -O.

AU - Ehrenreich, D.

AU - Erikson, A.

AU - Fossati, L.

AU - Fridlund, M.

AU - Gandolfi, D.

AU - Gillon, M.

AU - Güdel, M.

AU - Günther, M. N.

AU - Harre, J. V.

AU - Heitzmann, A.

AU - Helling, Ch

AU - Hoyer, S.

AU - Isaak, K. G.

AU - Kiss, L. L.

AU - Lam, K. W. F.

AU - Laskar, J.

AU - Lecavelier des Etangs, A.

AU - Magrin, D.

AU - Maxted, P. F. L.

AU - Mischler, H.

AU - Mordasini, C.

AU - Nascimbeni, V.

AU - Olofsson, G.

AU - Ottensamer, R.

AU - Palle, E.

AU - Peter, G.

AU - Piotto, G.

AU - Pollacco, D.

AU - Ragazzoni, R.

AU - Rando, N.

AU - Rauer, H.

AU - Ribas, I.

AU - Salmon, S.

AU - Ségransan, D.

AU - Simon, A. E.

AU - Stalport, M.

AU - Steinberger, M.

AU - Szabó, Gy M.

AU - Thomas, N.

AU - Udry, S.

AU - Ulmer, B.

AU - Van Grootel, V.

AU - Venturini, J.

AU - Villaver, E.

AU - Walton, N. A.

AU - Zingales, T.

N1 - Funding: V.Si., G.Sc., G.Br., I.Pa., L.Bo., V.Na., G.Pi., R.Ra., and T.Zi. acknowledge support from CHEOPS ASI-INAF agreement no. 2019-29-HH.0. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, program J4595-N. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). S.G.S. acknowledges support from FCT through FCT contract no. CEECIND/00826/2018 and POPH/FSE (EC). A.Br. was supported by the SNSA. L.Ca. and C.He. acknowledge support from the European Union H2020- MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON). T.Wi. acknowledges support from the UKSA and the University of Warwick. This work was supported by FCT – Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020 through the research grants UIDB/04434/2020, UIDP/04434/2020, 2022.06962.PTDC. O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. N.C.Sa. acknowledges funding by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Y.Al. acknowledges support from the Swiss National Science Foundation (SNSF) under grant 200020_192038. R.Al., D.Ba., E.Pa., and I.Ri. acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 and the ERDF “A way of making Europe” through projects PID2019-107061GB-C61, PID2019-107061GB-C66, PID2021-125627OB-C31, and PID2021-125627OB-C32, from the Centre of Excellence “Severo Ochoa” award to the Instituto de Astrofísica de Canarias (CEX2019-000920-S), from the Centre of Excellence “María de Maeztu” award to the Institut de Ciències de l’Espai (CEX2020-001058-M), and from the Generalitat de Catalunya/CERCA programme. S.C.C.B. acknowledges support from FCT through FCT contracts nr. IF/01312/2014/CP1215/CT0004. X.B., S.C., D.G., M.F. and J.L. acknowledge their role as ESA-appointed CHEOPS science team members. C.Br. and A.Si. acknowledge support from the Swiss Space Office through the ESA PRODEX program. A.C.C. acknowledges support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. This project was supported by the CNES. The Belgian participation to CHEOPS has been supported by the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Program, and by the University of Liège through an ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. L.D. is an F.R.S.-FNRS Postdoctoral Researcher. B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (project FOUR ACES. grant agreement no. 724427). It has also been carried out in the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). D.E. acknowledges financial support from the Swiss National Science Foundation for project 200021_200726. M.F. and C.M.P. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). D.G. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseousor rocky? Unveiling the nature of small worlds”. M.G. is an F.R.S.-FNRS Senior Research Associate. M.N.G. is the ESA CHEOPS Project Scientist and Mission Representative, and as such also responsible for the Guest Observers (GO) Programme. M.N.G. does not relay proprietary information between the GO and Guaranteed Time Observation (GTO) Programmes, and does not decide on the definition and target selection of the GTO Programme. S.H. gratefully acknowledges CNES funding through the grant 837319. K.G.I. is the ESA CHEOPS Project Scientist and is responsible for the ESA CHEOPS Guest Observers Programme. She does not participate in, or contribute to, the definition of the Guaranteed Time Programme of the CHEOPS mission through which observations described in this paper have been taken, nor to any aspect of target selection for the programme. K.W.F.L. was supported by Deutsche Forschungsgemeinschaft grants RA714/14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. This work was granted access to the HPC resources of MesoPSL financed by the Region Ile de France and the project Equip@Meso (reference ANR-10-EQPX29-01) of the programme Investissements d’Avenir supervised by the Agence Nationale pour la Recherche. P.M. acknowledges support from STFC research grant number ST/M001040/1. Gy.M.Sz. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Experiment Agreement No. 4000137122, the Lendület LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. V.V.G. is an F.R.S-FNRS Research Associate. N.A.W. acknowledges UKSA grant ST/R004838/1. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA’s Science Mission Directorate.

PY - 2024/3

Y1 - 2024/3

N2 - 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 (ε = 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.

AB - 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 (ε = 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.

KW - Planets and satellites: atmospheres

KW - Planets and satellites: gaseous planets

KW - Planets and satellites: individual: KELT-20 b

KW - Planets and satellites: individual: MASCARA-2 b

KW - Techniques: photometric

U2 - 10.1051/0004-6361/202347533

DO - 10.1051/0004-6361/202347533

M3 - Article

AN - SCOPUS:85186624090

SN - 0004-6361

VL - 683

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A1

ER -

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

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AO2 - Professor Andrew Cameron: Project AO2 - Andrew Cameron

Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021

Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation

Datasets

KELT-20b/MASCARA-2b CHEOPS light curve

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