CHEOPS precision phase curve of the Super-Earth 55 Cancri e^★

¹ Center for Space and Habitability, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
e-mail: morrisbrettm@gmail.com
² Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
³ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
⁴ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
⁵ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
⁶ Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
⁷ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁸ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹⁰ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
¹² Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹³ Depto. de Astrofísica, Centro de Astrobiologia (CSIC-INTA), ESAC campus, 28692 Villanueva de la Cãda (Madrid), Spain
¹⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁵ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁶ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁷ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁸ Admatis, Miskok, Hungary
¹⁹ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
²⁰ Université de Paris, Institut de physique du globe de Paris, CNRS, 75005 Paris, France
²¹ Lund Observatory, Dept. of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden
²² Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
²³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
²⁴ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125, Torino, Italy
²⁵ Center for Astronomy and Astrophysics, Technical University Berlin, Hardenberstrasse 36, 10623 Berlin, Germany
²⁶ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
²⁷ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
²⁸ IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
²⁹ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis blvd. Arago, 75014 Paris, France
³⁰ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³¹ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
³² Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
³³ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
³⁴ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
³⁵ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
³⁶ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³⁷ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
³⁸ ESTEC, European Space Agency, 2201AZ, Noordwijk, The Netherlands
³⁹ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
⁴⁰ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴¹ MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁴³ Ingenieurbüro Ulmer – Technische Informatik, Im Technologiepark 1, 15236 Frankfurt, Germany
⁴⁴ Airbus DS Spain
⁴⁵ Science and Operations Department – Science Division (SCI-SC), Directorate of Science, European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), The Netherlands
⁴⁶ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁴⁷ Sydney Institute for Astronomy, School of Physics A29, University of Sydney, NSW 2006, Australia
⁴⁸ Division Technique INSU, BP 330, 83507 La Seyne cedex, France

Received: 26 March 2021
Accepted: 11 June 2021

Abstract

Context. 55 Cnc e is a transiting super-Earth (radius 1.88 R_⊕ and mass 8 M_⊕) orbiting a G8V host star on a 17-h orbit. Spitzer observations of the planet’s phase curve at 4.5 μm revealed a time-varying occultation depth, and MOST optical observations are consistent with a time-varying phase curve amplitude and phase offset of maximum light. Both broadband and high-resolution spectroscopic analyses are consistent with either a high mean molecular weight atmosphere or no atmosphere for planet e. A long-term photometric monitoring campaign on an independent optical telescope is needed to probe the variability in this system.

Aims. We seek to measure the phase variations of 55 Cnc e with a broadband optical filter with the 30 cm effective aperture space telescope CHEOPS and explore how the precision photometry narrows down the range of possible scenarios.

Methods. We observed 55 Cnc for 1.6 orbital phases in March of 2020. We designed a phase curve detrending toolkit for CHEOPS photometry which allowed us to study the underlying flux variations in the 55 Cnc system.

Results. We detected a phase variation with a full-amplitude of 72 ± 7 ppm, but did not detect a significant secondary eclipse of the planet. The shape of the phase variation resembles that of a piecewise-Lambertian; however, the non-detection of the planetary secondary eclipse, and the large amplitude of the variations exclude reflection from the planetary surface as a possible origin of the observed phase variations. They are also likely incompatible with magnetospheric interactions between the star and planet, but may imply that circumplanetary or circumstellar material modulate the flux of the system.

Conclusions. This year, further precision photometry of 55 Cnc from CHEOPS will measure variations in the phase curve amplitude and shape over time.