11institutetext:  Universidade Federal do Rio de Janeiro - Observatório do
Valongo, Ladeira Pedro Antônio 43, CEP 20.080-090 Rio de Janeiro - RJ, Brazil
11email<EMAIL_ADDRESS>22institutetext:  Observatório Nacional/MCTI, R.
General José Cristino 77, CEP 20921-400 Rio de Janeiro - RJ, Brazil
33institutetext:  Laboratório Interinstitucional de e-Astronomia - LIneA, Rua
Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil 44institutetext:
INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania,
Italy 55institutetext:  Institute of Physics, Federal University of
Uberlândia, Uberlândia-MG, Brazil 66institutetext:  UNESP - São Paulo State
University, Grupo de Dinâmica Orbital e Planetologia, CEP 12516-410,
Guaratinguetá, SP, Brazil 77institutetext:  LESIA, Observatoire de Paris,
Université PSL, Sorbonne Université, Université de Paris, CNRS, 92190 Meudon,
France 88institutetext:  Physikalisches Institut, University of Bern,
Sidlerstrasse 5, 3012 Bern, Switzerland 99institutetext:  Center for Space and
Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern,
Switzerland 1010institutetext:  Institut Polytechnique des Sciences Avancées
IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
1111institutetext:  Institut de Mécanique Céleste et de Calcul des
Éphémérides, IMCCE, Observatoire de Paris, PSL Research University,
CNRS,Sorbonne Universités, UPMC Univ Paris 06, Univ. Lille, 77, Av. Denfert-
Rochereau, 75014 Paris, France 1212institutetext:  Astrophysics Group, Keele
University, Staffordshire, ST5 5BG, United Kingdom 1313institutetext:  Federal
University of Technology - Paraná (UTFPR / DAFIS), Rua Sete de Setembro, 3165,
CEP 80230-901, Curitiba, PR, Brazil 1414institutetext:  ETH Zurich, Department
of Physics, Wolfgang-Pauli-Strasse 2, CH-8093 Zurich, Switzerland
1515institutetext:  Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3
0HE, UK 1616institutetext:  Instituto de Astrofisica e Ciencias do Espaco,
Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
1717institutetext:  Instituto de Astrofísica de Andalucía, IAA-CSIC, Glorieta
de la Astronomía s/n, 18008 Granada, Spain 1818institutetext:  Department of
Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm,
Sweden 1919institutetext:  Centre for Exoplanet Science, SUPA School of
Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16
9SS, UK 2020institutetext:  Observatoire Astronomique de l’Université de
Genève, Chemin Pegasi 51, Versoix, Switzerland 2121institutetext:
Observatoire de la Côte d’Azur, Laboratoire Lagrange UMR7293 CNRS, Nice,
France 2222institutetext:  naXys, University of Namur, 8 Rempart de la Vierge,
Namur, B-5000, Belgium 2323institutetext:  Science and Operations Department -
Science Division (SCI-SC), Directorate of Science, European Space Agency
(ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1,
2201-AZ Noordwijk, The Netherlands 2424institutetext:  Reedy Creek
Observatory, Gold Coast, Queensland, Australia 2525institutetext:  Trans-
Tasman Occultation Alliance (TTOA), Wellington, PO Box 3181, New Zealand
2626institutetext:  Instituto de Astrofisica de Canarias, 38200 La Laguna,
Tenerife, Spain 2727institutetext:  Departamento de Astrofisica, Universidad
de La Laguna, 38206 La Laguna, Tenerife, Spain 2828institutetext:  Institut de
Ciencies de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193
Bellaterra, Spain 2929institutetext:  Institut d’Estudis Espacials de
Catalunya (IEEC), 08034 Barcelona, Spain 3030institutetext:  Admatis, 5. Kandó
Kálmán Street, 3534 Miskolc, Hungary 3131institutetext:  Depto. de
Astrofisica, Centro de Astrobiologia (CSIC-INTA), ESAC campus, 28692
Villanueva de la Cañada (Madrid), Spain 3232institutetext:  Departamento de
Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do
Campo Alegre, 4169-007 Porto, Portugal 3333institutetext:  Space Research
Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz,
Austria 3434institutetext:  Université Grenoble Alpes, CNRS, IPAG, 38000
Grenoble, France 3535institutetext:  Institute of Planetary Research, German
Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
3636institutetext:  Université de Paris, Institut de physique du globe de
Paris, CNRS, F-75005 Paris, France 3737institutetext:  Centre for Mathematical
Sciences, Lund University, Box 118, 221 00 Lund, Sweden 3838institutetext:
Aix Marseille Univ, CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388
Marseille, France 3939institutetext:  Astrobiology Research Unit, Université
de Liège, Allée du 6 Août 19C, B-4000 Liège, Belgium 4040institutetext:  Space
sciences, Technologies and Astrophysics Research (STAR) Institute, Université
de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium 4141institutetext:  Leiden
Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The
Netherlands 4242institutetext:  Department of Space, Earth and Environment,
Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala,
Sweden 4343institutetext:  Dipartimento di Fisica, Universita degli Studi di
Torino, via Pietro Giuria 1, I-10125, Torino, Italy 4444institutetext:
University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180
Vienna, Austria 4545institutetext:  Department of Physics, University of
Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom 4646institutetext:
Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121
Budapest, Konkoly Thege Miklós út 15-17, Hungary 4747institutetext:  ELTE
Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117
4848institutetext:  IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ.,
Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
4949institutetext:  Institut d’astrophysique de Paris, UMR7095 CNRS,
Université Pierre & Marie Curie, 98bis blvd. Arago, 75014 Paris, France
5050institutetext:  INAF, Osservatorio Astronomico di Padova, Vicolo
dell’Osservatorio 5, 35122 Padova, Italy 5151institutetext:  Department of
Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna,
Austria 5252institutetext:  Institute of Optical Sensor Systems, German
Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
5353institutetext:  Dipartimento di Fisica e Astronomia ”Galileo Galilei”,
Universita degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova,
Italy 5454institutetext:  ESTEC, European Space Agency, 2201AZ, Noordwijk, NL
5555institutetext:  Zentrum für Astronomie und Astrophysik, Technische
Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
5656institutetext:  Institut für Geologische Wissenschaften, Freie Universität
Berlin, 12249 Berlin, Germany 5757institutetext:  ELTE Eötvös Loránd
University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre h.
u. 112, Hungary 5858institutetext:  MTA-ELTE Exoplanet Research Group, 9700
Szombathely, Szent Imre h. u. 112, Hungary 5959institutetext:  Institute of
Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, United
Kingdom

# A stellar occultation by the transneptunian object (50000) Quaoar observed
by CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.

B. E. Morgado ${}^{\href https://orcid.org/0000-0003-0088-1808}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. G.
Bruno ${}^{\href https://orcid.org/0000-0002-3288-0802}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. A. R. Gomes-Júnior
${}^{\href https://orcid.org/0000-0002-3362-2127}$ A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. I. Pagano ${}^{\href
https://orcid.org/0000-0001-9573-4928}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. B. Sicardy ${}^{\href
https://orcid.org/0000-0003-1995-0842}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. Fortier ${}^{\href
https://orcid.org/0000-0001-8450-3374}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. J. Desmars ${}^{\href
https://orcid.org/0000-0002-2193-8204}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. P. F. L. Maxted ${}^{\href
https://orcid.org/0000-0003-3794-1317}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. F. Braga-Ribas ${}^{\href
https://orcid.org/0000-0003-2311-2438}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Queloz ${}^{\href
https://orcid.org/0000-0002-3012-0316}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. S. G. Sousa ${}^{\href
https://orcid.org/0000-0001-9047-2965}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. J. L. Ortiz ${}^{\href
https://orcid.org/0000-0002-8690-2413}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. Brandeker ${}^{\href
https://orcid.org/0000-0002-7201-7536}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. Collier Cameron ${}^{\href
https://orcid.org/0000-0002-8863-7828}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. C. L. Pereira ${}^{\href
https://orcid.org/0000-0003-1000-8113}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. H. G. Florén A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. N.
Hara ${}^{\href https://orcid.org/0000-0001-9232-3314}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. D. Souami ${}^{\href
https://orcid.org/0000-0003-4058-0815}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. K. G. Isaak ${}^{\href
https://orcid.org/0000-0001-8585-1717}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. G. Olofsson ${}^{\href
https://orcid.org/0000-0003-3747-7120}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. P. Santos-Sanz ${}^{\href
https://orcid.org/0000-0002-1123-983X}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. T. G. Wilson ${}^{\href
https://orcid.org/0000-0001-8749-1962}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. J. Broughton A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. Y.
Alibert ${}^{\href https://orcid.org/0000-0002-4644-8818}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. R.
Alonso ${}^{\href https://orcid.org/0000-0001-8462-8126}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. G.
Anglada ${}^{\href https://orcid.org/0000-0002-3645-5977}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. T.
Bárczy ${}^{\href https://orcid.org/0000-0002-7822-4413}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. D.
Barrado ${}^{\href https://orcid.org/0000-0002-5971-9242}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. S.
C. C. Barros ${}^{\href https://orcid.org/0000-0003-2434-3625}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. W.
Baumjohann ${}^{\href https://orcid.org/0000-0001-6271-0110}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. M.
Beck ${}^{\href https://orcid.org/0000-0003-3926-0275}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. T. Beck A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. W.
Benz ${}^{\href https://orcid.org/0000-0001-7896-6479}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. N. Billot ${}^{\href
https://orcid.org/0000-0003-3429-3836}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. X. Bonfils ${}^{\href
https://orcid.org/0000-0001-9003-8894}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. C. Broeg ${}^{\href
https://orcid.org/0000-0001-5132-2614}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. J. Cabrera A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. S. Charnoz ${}^{\href
https://orcid.org/0000-0002-7442-491X}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. S. Csizmadia ${}^{\href
https://orcid.org/0000-0001-6803-9698}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. B. Davies ${}^{\href
https://orcid.org/0000-0001-6080-1190}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. Deleuil ${}^{\href
https://orcid.org/0000-0001-6036-0225}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. L. Delrez ${}^{\href
https://orcid.org/0000-0001-6108-4808}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. O. D. S. Demangeon ${}^{\href
https://orcid.org/0000-0001-7918-0355}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. B. O. Demory ${}^{\href
https://orcid.org/0000-0002-9355-5165}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Ehrenreich ${}^{\href
https://orcid.org/0000-0001-9704-5405}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. Erikson A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. L. Fossati ${}^{\href
https://orcid.org/0000-0003-4426-9530}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. Fridlund ${}^{\href
https://orcid.org/0000-0002-0855-8426}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Gandolfi ${}^{\href
https://orcid.org/0000-0001-8627-9628}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. Gillon ${}^{\href
https://orcid.org/0000-0003-1462-7739}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. Güdel A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. K. Heng ${}^{\href
https://orcid.org/0000-0003-1907-5910}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. S. Hoyer ${}^{\href
https://orcid.org/0000-0003-3477-2466}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. L. L. Kiss A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. J. Laskar ${}^{\href
https://orcid.org/0000-0003-2634-789X}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. Lecavelier des Etangs
${}^{\href https://orcid.org/0000-0002-5637-5253}$ A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. M. Lendl ${}^{\href
https://orcid.org/0000-0001-9699-1459}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. C. Lovis ${}^{\href
https://orcid.org/0000-0001-7120-5837}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Magrin ${}^{\href
https://orcid.org/0000-0003-0312-313X}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. L. Marafatto A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. V.
Nascimbeni ${}^{\href https://orcid.org/0000-0001-9770-1214}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. R.
Ottensamer ${}^{\href https://orcid.org/0000-0001-5684-5836}$ A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. E.
Pallé ${}^{\href https://orcid.org/0000-0003-0987-1593}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. G. Peter ${}^{\href
https://orcid.org/0000-0001-6101-2513}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Piazza A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. G. Piotto ${}^{\href
https://orcid.org/0000-0002-9937-6387}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Pollacco A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. R. Ragazzoni ${}^{\href
https://orcid.org/0000-0002-7697-5555}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. N. Rando A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. F. Ratti A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. H.
Rauer ${}^{\href https://orcid.org/0000-0002-6510-1828}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. C. Reimers ${}^{\href
https://orcid.org/0000-0002-2334-1620}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. I. Ribas ${}^{\href
https://orcid.org/0000-0002-6689-0312}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. N. C. Santos ${}^{\href
https://orcid.org/0000-0003-4422-2919}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. G. Scandariato ${}^{\href
https://orcid.org/0000-0003-2029-0626}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. D. Ségransan ${}^{\href
https://orcid.org/0000-0003-2355-8034}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. E. Simon ${}^{\href
https://orcid.org/0000-0001-9773-2600}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. A. M. S. Smith ${}^{\href
https://orcid.org/0000-0002-2386-4341}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. M. Steller ${}^{\href
https://orcid.org/0000-0003-2459-6155}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. G. M. Szabó A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. N. Thomas A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021. S.
Udry ${}^{\href https://orcid.org/0000-0001-7576-6236}$ A stellar occultation
by the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021.A stellar occultation by
the transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This
article uses data from CHEOPS programme CH_PR100021. V. Van Grootel ${}^{\href
https://orcid.org/0000-0003-2144-4316}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. N. A. Walton ${}^{\href
https://orcid.org/0000-0003-3983-8778}$ A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021.A stellar occultation by the
transneptunian object (50000) Quaoar observed by CHEOPS††thanks: This article
uses data from CHEOPS programme CH_PR100021. K. Westerdorff A stellar
occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.A
stellar occultation by the transneptunian object (50000) Quaoar observed by
CHEOPS††thanks: This article uses data from CHEOPS programme CH_PR100021.

(Received 09/06/2022; accepted 09/08/2022)

###### Abstract

Context. Stellar occultation is a powerful technique that allows the
determination of some physical parameters of the occulting object. The result
depends on the photometric accuracy, the temporal resolution, and the number
of chords obtained. Space telescopes can achieve high photometric accuracy as
they are not affected by atmospheric scintillation.

Aims. Using ESA’s CHEOPS space telescope, we observed a stellar occultation by
the transneptunian object (50000) Quaoar. We compare the obtained chord with
previous occultations by this object and determine its astrometry with sub-
milliarcsecond precision. Also, we determine upper limits to the presence of a
global methane atmosphere on the occulting body.

Methods. We predicted and observed a stellar occultation by Quaoar using the
CHEOPS space telescope. We measured the occultation light curve from this
dataset and determined the dis- and reappearance of the star behind the
occulting body. Furthermore, a ground-based telescope in Australia was used to
constrain Quaoar’s limb. Combined with results from previous works, these
measurements allowed us to obtain a precise position of Quaoar at the
occultation time.

Results. We present the results obtained from the first stellar occultation by
a transneptunian object (TNO) using a space telescope orbiting Earth; it was
the occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light
curve to obtain a surface pressure upper limit of 85 nbar for the detection of
a global methane atmosphere. Also, combining this observation with a ground-
based observation, we fitted Quaoar’s limb to determine its astrometric
position with an uncertainty below 1.0 mas.

Conclusions. This observation is the first of its kind, and it shall be
considered as a proof of concept of stellar occultation observations of
transneptunian objects with space telescopes orbiting Earth. Moreover, it
shows significant prospects for the James Webb Space Telescope.

###### Key Words.:

Methods: observational – Techniques: photometry – Occultations – Minor
planets, asteroids: individual: Quaoar

##  1 Introduction

Stellar occultations happen when a body passes in front of a star as viewed by
an observer. The detection of these events allow the determination of 2D
apparent sizes and shapes with kilometre uncertainties (Sicardy et al. 2011).
Also, with these events, we can probe the vicinity of the occulting object in
search for material, such as rings (Braga-Ribas et al. 2014; Ortiz et al.
2017), and even detect, characterise, or determine limits to atmospheres
(Marques Oliveira et al. 2022; Meza et al. 2019; Arimatsu et al. 2019; Ortiz
et al. 2012). From an astrometric point of view, these events can provide
highly accurate positions of the occulting object, with uncertainties of the
order of a few milliarcseconds (mas, Rommel et al. 2020).

This Letter details the analysis of the stellar occultation by the large
transneptunian object (TNO; 50000) Quaoar on 2020 June 11. Quaoar belongs to
the dynamical class of Cubewanos. It has a semi-major axis of 43.51 au, an
orbital eccentricity of 0.035, and an inclination of 7.98 degrees. Quaoar was
discovered in 2002 by Brown & Trujillo (2004). These authors estimated
Quaoar’s diameter to be about 1260 $\pm$ 190 km based on Hubble Space
Telescope (HST) images. From previous stellar occultations, Braga-Ribas et al.
(2013) obtained an area equivalent diameter of 1110 $\pm$ 5.0 km under the
assumption that Quaoar is a Maclaurin spheroid. Also, thermal models based on
Herschel data obtained an area equivalent diameter of 1074 $\pm$ 38 km
(Fornasier et al. 2013).

In 2007, a small moon orbiting Quaoar was discovered (Brown & Suer 2007), and
was later named Weywot. This satellite orbits Quaoar with a semi-major axis of
$1.45\times 10^{4}$ km and a period of $12.047$ days. From its orbital motion,
the mass of Quaoar was estimated as $1.65\times 10^{21}$ kg (Fraser & Brown
2010; Fraser et al. 2013; Vachier et al. 2012).

The occultation reported in the present Letter was observable from Australia
and was detected by ESA’s CHaracterising ExOPlanet Satellite (CHEOPS, Benz et
al. 2020) space telescope111Webpage:
http://www.esa.int/Science_Exploration/Space_Science/Cheops. CHEOPS is a
mission dedicated to studying exoplanets using the transit technique. This
satellite was launched in December 2019, and is in a Sun-synchronous orbit,
about 700 km above Earth. It has a 32 cm diameter Ritchey-Chrétien telescope
(f/8) with a single, frame-transfer, back-illuminated CCD detector in its
focal plane. Its focal plane is defocussed to deliver a large point spread
function (PSF), where 90% of the stellar flux spreads within a radial aperture
of 16 pixels. The CCD detector has 1024 $\times$ 1024 pixels and a pixel pitch
of 13 $\mu$m. There is no filter in the optical path, resulting in a bandpass
between 0.33 and 1.10 microns. This system was designed to deliver photometric
measurements with high accuracy.

For the first time, we predicted and detected a stellar occultation by a TNO
as observed by a space telescope orbiting Earth. This achievement was made
possible thanks to the collaborative effort of the European Research Council
(ERC) Lucky Star project222Webpage: https://lesia.obspm.fr/lucky-
star/index.php and the ESA CHEOPS mission. Through this observation we are
able to probe the object’s vicinity, avoiding interference from Earth’s
atmosphere, detect a limit of a methane atmosphere around Quaoar, and
determine the astrometric position of this large TNO with an uncertainty at
the sub-mas level (less than 5 km at Quaoar’s distance).

section 2 contains details about the prediction and observation of the
occultation event. In section 3, we describe the analysis of the images,
determination of the light curve, and fitting the immersion (disappearance)
and emersion (reappearance) times. section 4 details the geometric
reconstruction of the event and a determination of Quaoar’s astrometric
position. Finally, our discussion and final remarks can be found in section 5.

##  2 Prediction and observation

The event presented here was predicted in the framework of the ERC Lucky Star
project. It uses the star’s position available in the Gaia catalogue (Gaia
Collaboration et al. 2016b, a, 2018). Quaoar’s ephemeris was pinned down to
the 5 mas accuracy level ($\sim$150 km at Quaoar’s distance), using the
Numerical Integration of the Motion of an Asteroid (nima, Desmars et al. 2015)
integrator fed by observations in the Minor Planet Center333Webpage:
https://www.minorplanetcenter.net/iau/mpc.html (MPC) database and
astrometrical positions derived from previous stellar occultations (Braga-
Ribas et al. 2019, 2013).

Table 1 contains some general information about the June 2020 occultation,
such as the Gaia Source ID of the occulted star, its G magnitude, and its
position at the occultation epoch considering the robust propagation as
suggested by Butkevich & Lindegren (2014), also considering the correct proper
motion as discussed by Cantat-Gaudin & Brandt (2021). In this table we also
added information about the occulting object, such as its positions in the
occultation instant and visual magnitude.

Table 1: Information about the occultation by Quaoar on 2020 June 11. Parameter | Value
---|---
GAIA EDR3 Source | 4146202445050212352
Star’s Mag G | 12.667 $\pm$ 0.003
Star’s RA |  -18 15 03.055795 $\pm$ 0.09 mas
Star’s Dec | -15 15 04.946070 $\pm$ 0.06 mas
Star’s diameter | 0.03 mas / 0.97 km
Occ. date and time | 2020-06-11 16:27:25.5 UTC
Quaoar’s RA(a) |  -18 15 03.0717 $\pm$ 7 mas
Quaoar’s Dec(a) | -15 15 04.9410 $\pm$ 3 mas
Quaoar’s distance(a) | 41.840957 au
Quaoar’s Mag V |  $\sim$18.9
Shadow’s velocity | -23.98 km/s
a The used Quaoar ephemeris was the nima_v14 available
at the ERC Lucky Star Webpage.

Figure 1 shows the prediction map for the occultation event. The red line on
the right side of the map shows the position of CHEOPS from 16:22 to 16:33
UTC, and the green segment shows when and where CHEOPS observed the
occultation (positive chord). The red dot represents the position of the
ground-based observer J. Broughton, in Mount Carbine, Australia (144∘ 52′
29.4′′ E, 16∘ 27′ 58.7′′ S), who observed the star under a clear sky with a
25-cm telescope, but did not see the expected occultation, thus it is a
negative chord.

Figure 1: Prediction map of the Quaoar event on 2020 June 11, the black arrow
on the lower left corner shows the direction of the shadow’s movement. The
blue lines stand for the shadow limits, and the black dots are the centre of
the shadow, separated by one minute, with the biggest one representing the
geocentric closest approach time. The red dot on the map represents the
position of the ground-based observer who participated in this campaign. The
red line on the right side of the map shows the projected position of CHEOPS
from 16:22 to 16:33 UTC, two consecutive red dots are separated by one minute
in time, and the red arrow emphasises the direction of motion. The green line
shows when and where CHEOPS obtained the positive chord.

The restituted CHEOPS ephemeris that was used contains its state vectors ($X$,
$Y$, $Z$, $\dot{X}$, $\dot{Y}$, and $\dot{Z}$) relative to the geocentre, with
axes in the ICRS, between 2020 June 11 06:51 UTC and 2020 June 12 23:56 UTC.
The observation was done between 15:47:55.069 and 16:46:05.024 UTC with an
exposure time of 3.0 seconds and a mean cycle of 3.024 seconds. It resulted in
1148 frames where the target star and the TNO were measured in the same
aperture. CHEOPS ephemeris and the observed data are available in its
archive444Webpage: https://cheops-archive.astro.unige.ch/archive_browser/.

##  3 Light curve analysis and times

CHEOPS was designed for exoplanet transit events, and the typical time
resolution is 30 – 60s, and a 200-pixel diameter sub-image was downloaded for
the photometry. However, to avoid saturation for brighter stars, shorter
exposure times can be chosen, and the images were stacked on board before
being downloaded. In addition, smaller images – called imagettes – with a size
of only 50 pixels in diameter, are provided for each exposure. Because of the
(deliberately) de-focussed image, this is just enough to allow for photometry
to enable high time resolution photometry. In the present case, the time
resolution is 3s, and the reduction steps are the following: bias subtraction,
flat-fielding, non-linearity correction, pointing jitter calculation, and
photometry.

First, the bias was determined from the overscan data provided with each sub-
image. The bias is stable, and no uncertainty was introduced by interpolation
to the 14 times more frequent imagettes. Then, we applied flat-fielding, which
depends on the wavelength due to CHEOPS’s broad spectral response. Therefore,
the applied flat field was weighted to match the spectral energy distribution
of the star (in the present case, the effective temperature was 5040 K).

The needed non-linearity correction is a minor correction based on pre-launch
measurements (Deline 2019; Deline et al. 2020; Futyan et al. 2020). For the
background subtraction, we need to consider that the imagettes are too small
to determine the background (basically the zodiacal light, but also the PSF
wings of field stars). For this reason, sub-images were used for background
calculation, and the background for each imagette was interpolated. The
pointing jitter was evaluated by tracking the position of one of the three
bright peaks in the PSF. The jitter amplitude was typically less than $\pm$
0.5 pixels.

Finally, the photometry was done considering that the Field of View (FoV)
around the target star is crowded. So, to minimise the contamination from
field stars, we used an aperture mimicking the PSF of the star rather than
using a standard circular aperture. The total number of pixels in this mask
was 852.

Observations made on ground by J. Broughton’s were analysed using the Platform
for Reduction of Astronomical Images Automatically (PRAIA, Assafin et al.
2011). The occulted star was measured with a circular aperture and nearby
stars were used as photometric calibrators to correct for sky fluctuations.

After normalising the light curve, we obtained the immersion and emersion
times using Stellar Occultation Reduction and Analysis (sora, Gomes-Júnior et
al. 2022)555Webpage: https://sora.readthedocs.io/. This software fits an
occultation model that considers a sharp-edge box model convolved with Fresnel
diffraction, the stellar diameter (projected at the body’s distance), CCD
bandwidth, and finite integration time. The light curves and the fitted models
are available in CDS.

Figure 2 contains the normalised light curves and the fitted models. The
obtained immersion and emersion times were 16:27:08.199 $\pm$ 0.020 and
16:27:43.556 $\pm$ 0.020, resulting in a chord duration of 35.357 $\pm$ 0.040
seconds. The minimum $\chi^{2}$ per degree of freedom obtained was 0.945.
CHEOPS light curve standard deviation outside the event was 0.76%. Usually,
only space telescopes can acquire such high photometric precision. Broughton’s
negative observation was separated into two blocks. The first was obtained
between 16:29:36.64 and 16:32:02.08 UTC, and the second between 16:32:16.77
and 16:33:02.05 UTC, both with exposures of 0.16 seconds. Broughton’s light
curve has a standard deviation of 14.74%. A fairer comparison can be made if
we stack Broughton’s light curve to have a similar exposure time as CHEOPS’
light curve (e.g. 3 seconds); for that, we stacked 19 data points
($19\leavevmode\nobreak\ \times\leavevmode\nobreak\ 0.16\leavevmode\nobreak\
s\leavevmode\nobreak\ =\leavevmode\nobreak\ 3.04\leavevmode\nobreak\ s$) and
achieved a standard deviation of 4.2%.

Figure 2: Normalised light curves on 2020 June 11 during the Quaoar’s stellar
occultation relative to the closest approach (CA) time for each observer. The
upper panel contains the CHEOPS light curve (black dots) and the fitted model
(red line), and the middle panel contains CHEOPS residuals, in the sense of
the observed flux minus the model. The bottom panel contains Broughton’s
negative light curve, where the grey line stands for the single images, and
the black line stands for the stack of 19 images, resulting in a better
signal-to-noise ratio.

The photometric accuracy obtained with CHEOPS for the occultation presented
here makes this light curve an interesting case study in searching for an
atmosphere around Quaoar. We determined an upper limit of a pure methane (CH4)
atmosphere using the ray-tracing method (Dias-Oliveira et al. 2015), the
obtained upper limit was 85 nbar. This large value is caused by the large
exposure time (3 seconds) and the fact that all the disappearance and
reappearance information happen during a single data point. Simulations where
the star disappearance happens in the limit between two data points shows that
we would have a detection limit of about 3 nbar in that scenario. The detailed
analysis can be found in Appendix A.

##  4 Geometric reconstruction of the event

The instants of disappearance and reappearance of the star behind the
occulting body are the moments where the line-of-sight observer star matches
the projected limb of the body. Therefore, the relative position between star
and body at these moments gives the bi-dimensional position ($f$, $g$) of the
limb relative to the body’s centre in a plane perpendicular to the line of
sight, the tangent plane. This projection was made with the sora package, and
it results in a chord’s size of 871.61 $\pm$ 0.99 km.

The obtained chord is compatible with the area equivalent diameter obtained by
stellar occultations (1110 km, Braga-Ribas et al. 2013) and with the diameter
derived from thermal data (1074 km, Fornasier et al. 2013). Each chord
extremity is a point at which we can fit the apparent shape of the occulting
object. As only one chord was recorded, we fitted the centre of the figure
($f_{0}$, $g_{0}$), allowing the shape to vary within the Maclaurin spheroid
solution proposed by Braga-Ribas et al. (2013), with an equatorial radius of
$581^{+12}_{-8}$ km, apparent oblateness varying between 0 and 0.114, and a
pole position angle between 0 and 180 degrees. This fit was done using sora,
with a method that is fully described in Gomes-Júnior et al. (2022). The
negative chord was used to eliminate solutions that would result in a positive
detection of the occultation by J. Broughton.

Figure 3 shows the best-fitted ellipses and their respective 1$\sigma$ region
as representatives of Quaoar’s limb. Two solutions can be obtained, one with
the centre north of the chord (at $f_{0}$ = $-$252 km and $g_{0}$ = $-$716 km,
in red), and the second with the centre to the south (at $f_{0}$ = $-$48 km
and $g_{0}$ = $+$81 km, in black). As can be seen in Table 1, the nima
software obtained an uncertainty of $\sim$212 km in RA and $\sim$90 km in
December for Quaoar ephemeris. Moreover, it is unlikely that the north
solution is the correct one as it is not consistent with the knowledge we have
about Quaoar’s orbit. Finally, we can shift the reference frame to the
geocentre and determine Quaoar’s astrometric geocentric position on 2020 June
11 at 16:27:25.500 UTC as

$\displaystyle RA$ $\displaystyle=$
$\displaystyle\phantom{-}18^{h}\leavevmode\nobreak\
15^{\prime}\leavevmode\nobreak\ 03^{\prime\prime}.0715863\pm
0.864\leavevmode\nobreak\ \textrm{mas},$ $\displaystyle DEC$ $\displaystyle=$
$\displaystyle-15^{\circ}\leavevmode\nobreak\ 15^{\prime}\leavevmode\nobreak\
04^{\prime\prime}.937760\leavevmode\nobreak\ \pm\leavevmode\nobreak\
0.729\leavevmode\nobreak\ \textrm{mas}.$

This position can be used to improve Quaoar’s ephemeris, which in turn helps
us to predict future, accurate stellar occultations for this object.

Figure 3: Best fitted limb to the CHEOPS chord (in blue) and ellipses within
their respective 1-$\sigma$ region. Two solutions can be obtained, one with
the centre north of the chord (in red), and another to the south (in black).
The black line stands for the preferred resulted central position of Quaoar
($f_{0},\leavevmode\nobreak\ g_{0}$) considering the centre to the south of
the chord. The red line is the unlikely northern solution. The solution in
black is the preferred solution as it agrees more with the expected orbit of
Quaoar based on the nima ephemeris and its uncertainty (yellow dashed region).
The green dashed line corresponds to the negative observation used to
eliminate some of the solutions that cross it (light grey ellipses).

As this was a single chord event, no further constraint on Quaoar’s shape was
obtained. However, the resulting pole position angle for Quaoar was restrained
to values between 14.2 $\pm$ 39.8 degrees due to J. Broughton’s negative
chord. This orientation is in agreement with Weywot’s orbital pole position
for the occultation date of $-$5.2 degrees, using the pole orientation
published by Vachier et al. (2012).

##  5 Discussion

Stellar occultations are transient events that allow us to obtain physical
parameters of the bodies in our Solar System. Networks of ground-based
telescopes have been used to observe such events and derive many relevant
results. Stellar occultations have also been observed by spacecrafts, such as
the Cassini mission (Li et al. 2014). However, these were mostly in loco
observations with events involving the objects the spacecrafts were visiting.

From space telescopes orbiting Earth, HST observed a stellar occultation by
Saturn and its rings in 1991, as shown in Elliot et al. (1993). Furthermore,
analysing HST Fine Guidance Sensors, two serendipitous occultations by small
Oort cloud objects were reported by Schlichting et al. (2009) and Schlichting
et al. (2012).

For the first time, we report on the detection of a stellar occultation by a
minor body as the primary target of the observation of a space telescope
orbiting Earth. We obtained a non-diametrical chord of 871.61 $\pm$ 0.99 km
for the TNO Quaoar, consistent with its previously published size. As a
result, we detected limits of a global methane atmosphere around Quaoar.
Finally, we obtained an astrometric position with an uncertainty better than 1
mas.

It is important to highlight that more ground-based stations could observe
this occultation. Combining space- and ground-based observation can provide
more constraints for the limb fitting and improve the result. Also, ground-
based observations will detect chords that are usually parallel to each other,
while the orientation of a space telescope will differ, which can be useful in
the limb fitting as shown in Figure 3. Finally, functions in the sora package
can be used to prepare automatic prediction pipelines based on the ephemeris
of the space telescope and occulting objects, as presented in Appendix B.

The space observation of the Quaoar occultation presented in this paper is the
first of its kind, and it serves as a proof of concept for future campaigns.
Space telescopes and CubeSat telescopes can be used in conjunction with
ground-based stations to detect stellar occultations. Space telescopes are not
affected by weather and they extend the range of the Earth where an
occultation can be observed. They can also help overcome the circumstances
where the shadow would mostly cross the ocean and limited ground-based
observations can be made, thus increasing the number of events observed. It is
important to highlight that CHEOPS’s diameter is modest, but it allows for a
photometric accuracy equivalent to what ground-based telescopes with much
larger apertures would obtain.

Moreover, as discussed by Santos-Sanz et al. (2016), the prospect for the
James Webb Space Telescope (JWST666Webpage:
https://jwst.nasa.gov/content/webbLaunch/index.html) is impressive. JWST’s
large primary mirror (6.5 metres in diameter) with a temporal sampling of 20
frames per second will allow for the precise characterisation of material
around the small bodies in our Solar System using stellar occultations, which
would include detecting faint rings and thin atmospheres within the occulting
bodies.

###### Acknowledgements.

This work was carried out within the “Lucky Star” umbrella that agglomerates
the efforts of the Paris, Granada and Rio teams, which is funded by the
European Research Council under the European Community’s H2020 (ERC Grant
Agreement No. 669416). CHEOPS is an ESA mission in partnership with
Switzerland with important contributions to the payload and the ground segment
from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain,
Sweden, and the United Kingdom. The CHEOPS Consortium would like to gratefully
acknowledge the support received by all the agencies, offices, universities,
and industries involved. Their flexibility and willingness to explore new
approaches were essential to the success of this mission. This research made
use of sora, a python package for stellar occultations reduction and analysis,
developed with the support of ERC Lucky Star and LIneA/Brazil, within the
collaboration of Rio-Paris-Granada teams. This work has made use of data from
the European Space Agency (ESA) mission Gaia
(https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and
Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). This study was financed
in part by the National Institute of Science and Technology of the e-Universe
project (INCT do e-Universo, CNPq grant 465376/2014-2). The following authors
acknowledge the respective i) CNPq grants: BEM 150612/2020-6; FB-R
314772/2020-0; ii) CAPES/Cofecub grant: BEM 394/2016-05. ii) FAPESP grants:
ARGJr 2018/11239-8; GBr, VNa, IPa, GPi, RRa, and GSc acknowledge support from
CHEOPS ASI-INAF agreement n. 2019-29-HH.0. ABr was supported by the SNSA. ACC
acknowledges support from STFC consolidated grant numbers ST/R000824/1 and
ST/V000861/1, and UKSA grant number ST/R003203/1. KGI 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. ACC and TW acknowledge support from STFC consolidated grant
numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. YA
and MJH acknowledge the support of the Swiss National Fund under grant
200020_172746. We acknowledge support from the Spanish Ministry of Science and
Innovation and the European Regional Development Fund through grants
ESP2016-80435-C2-1-R, ESP2016-80435-C2-2-R, PGC2018-098153-B-C33,
PGC2018-098153-B-C31, ESP2017-87676-C5-1-R, MDM-2017-0737 Unidad de Excelencia
Maria de Maeztu-Centro de Astrobiología (INTA-CSIC), as well as the support
of the Generalitat de Catalunya/CERCA programme. The MOC activities have been
supported by the ESA contract No. 4000124370. S.C.C.B. acknowledges support
from FCT through FCT contracts nr. IF/01312/2014/CP1215/CT0004. XB, SC, DG, MF
and JL acknowledge their role as ESA-appointed CHEOPS science team members.
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. This work was
supported by FCT - Fundação para a Ciência e a Tecnologia through national
funds and by FEDER through COMPETE2020 - Programa Operacional Competitividade
e Internacionalizacão by these grants: UID/FIS/04434/2019, UIDB/04434/2020,
UIDP/04434/2020, PTDC/FIS-AST/32113/2017 & POCI-01-0145-FEDER- 032113,
PTDC/FIS-AST/28953/2017 & POCI-01-0145-FEDER-028953, PTDC/FIS-AST/28987/2017 &
POCI-01-0145-FEDER-028987, O.D.S.D. is supported in the form of work contract
(DL 57/2016/CP1364/CT0004) funded by national funds through FCT. P.S-S.
acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00
“LEO-SBNAF” (MCIU/AEI/FEDER, UE). P.S-S. and J.L.O. acknowledge financial
support from the State Agency for Research of the Spanish MCIU through the
“Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de
Andalucía (SEV-2017-0709), they also acknowledge the financial support by the
Spanish grants AYA-2017-84637-R and PID2020-112789GB-I00, and the Proyectos de
Excelencia de la Junta de Andalucía 2012-FQM1776 and PY20-01309. B.-O.D.
acknowledges support from the Swiss National Science Foundation
(PP00P2-190080). 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). DE
acknowledges financial support from the Swiss National Science Foundation for
project 200021_200726. MF and CMP gratefully acknowledge the support of the
Swedish National Space Agency (DNR 65/19, 174/18). DG gratefully acknowledges
financial support from the CRT foundation under Grant No. 2018.2323 “Gaseous
or rocky? Unveiling the nature of small worlds”. M.G. is an F.R.S.-FNRS Senior
Research Associate. SH gratefully acknowledges CNES funding through the grant
837319. 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-EQPX-29-01) of the programme Investissements d’Avenir supervised by the
Agence Nationale pour la Recherche. ML acknowledges support of the Swiss
National Science Foundation under grant number PCEFP2_194576. PM acknowledges
support from STFC research grant number ST/M001040/1. This work was also
partially supported by a grant from the Simons Foundation (PI Queloz, grant
number 327127). IRI acknowledges support from the Spanish Ministry of Science
and Innovation and the European Regional Development Fund through grant
PGC2018-098153-B- C33, as well as the support of the Generalitat de
Catalunya/CERCA programme. S.G.S. acknowledge support from FCT through FCT
contract nr. CEECIND/00826/2018 and POPH/FSE (EC). GyMSz acknowledges the
support of the Hungarian National Research, Development and Innovation Office
(NKFIH) grant K-125015, a 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. VVG. is an F.R.S-FNRS Research Associate.
NAW acknowledges UKSA grant ST/R004838/1.

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##  Appendix A Quaoar’s atmospheric limit based on CHEOPS data

Using CHEOPS data for the 11 June 2020 occultation, we determined an upper
limit of Quaoar’s atmosphere. The model assumed was a pure methane (CH4)
atmosphere with a temperature gradient at the surface of $(dT/dz)_{\sf
surface}\leavevmode\nobreak\ =\leavevmode\nobreak\ 5.7$ K km-1, and an
isothermal upper branch at 102 K which is reached in about 10 km, see Figure
4. The tested model is consistent with the ones used in Braga-Ribas et al.
(2013) and Arimatsu et al. (2019). Quaoar was considered to be a sphere with a
radius of 555 km; any departure from that should be negligible at this level
of estimation.

Figure 4: Assumed temperature profile in Kelvin over radial distance in
kilometres of a pure methane (CH4) atmosphere.

A ray-tracing method (See Dias-Oliveira et al. (2015) and references therein)
was used to compute synthetic light curves convoluted with the instrumental
response (exposure time of 3 seconds). We varied the surface pressure
($P_{surface}$, in nbar) and the closest approach (CA, in kilometres) between
the star’s and Quaoar’s central position, and we performed Chi-squared
($\chi^{2}$) statistical tests to check the detection limit of a potential
methane atmosphere.

Figure 5: Chi-squared per degree of freedom ($\chi^{2}_{pdf}$) map vs. surface
pressure and CA distance. The inner dashed (resp. outer solid) green level
curve is the 1$\sigma$ (resp. 3$\sigma$) domain.

This analysis resulted in a surface pressure between 15 and 85 nbars for the
1$\sigma$ confidence level, and values between 0 and 95 nbars for 3$\sigma$.
So no significant value was obtained and only the 85 nbar as an upper limit
should be considered. Nonetheless, this limit is larger than the upper limits
determined by Braga-Ribas et al. (2013) of 20 nbar, and by Arimatsu et al.
(2019) of 6 nbar. This is caused by the large exposure time (3 seconds, about
75 km in radial distance in the sky plane) and the fact that all the
disappearance and reappearance information occurred within one exposure, so
the various models (with different pressure) are all contained in that
exposure. That makes the discrimination between pressures ineffective.

As a test, we simulated data where the star disappearance and reappearance
happens just at the limit between two exposures (the best case). This
simulation resulted in an upper limit of only 3 nbar, assuming the same model.
Is important to highlight that a smaller spatial resolution (e.g. smaller
temporal resolution, smaller event velocity, or grazing occultations) would
imply an even better result due to the photometric accuracy.

##  Appendix B Prediction of stellar occultations for CHEOPS

With the success achieved in observing the stellar occultation by Quaoar, we
predicted events to be observed by CHEOPS in the next months. We were granted
time to observe five stellar occultations by objects in the outer Solar
System. That was done in the context of the third Announcement of Opportunity.
The occultation prediction maps are shown in Figure 6-10. The path of CHEOPS
on space is given as the circle around Earth. Given the uncertainty as to the
exact position of CHEOPS at the occultation epoch, the predictions were made
by computing the probability of CHEOPS to observe the event, considering its
orbit is kept in a polar orbit with a movement just above the terminator of
the Earth, and fixing its orbital velocity. Ground-based campaigns are being
organised, and observations are planned to be made from Earth to complement
CHEOPS’ observation.

Figure 6: Prediction map of a stellar occultation by Triton on 2022 October
06. The path of CHEOPS is shown as the circle just above the Earth, with an
arrow indicating its sense of motion. Figure 7: Similar to Figure 6, but for
the occultation by Quaoar on 2023 May 10. Figure 8: Similar to Figure 6, but
for the occultation by Quaoar on 2023 May 26. Figure 9: Similar to Figure 6,
but for the occultation by 2002 MS4 on 2023 July 03. Figure 10: Similar to
Figure 6, but for the occultation by Quaoar on 2023 September 10.