Planets observed with CHEOPS

Author(s): M. Fridlund, I. Y. Georgieva, A. Bonfanti, Y. Alibert, C. M. Persson, D. Gandolfi, M. Beck, A. Deline, S. Hoyer, G. Olofsson, T. G. Wilson, O. Barragán, L. Fossati, A. J. Mustill, A. Brandeker, A. Hatzes, H. G. Florén, U. Simola, M. J. Hooton, R. Luque, S. G. Sousa, J. A. Egger, A. Antoniadis-Karnavas, S. Salmon, V. Adibekyan, R. Alonso, G. Anglada, T. Bárczy, D. Barrado Navascues, S. C.C. Barros, W. Baumjohann, T. Beck, W. Benz, X. Bonfils, C. Broeg, J. Cabrera, S. Charnoz, A. Collier Cameron, Sz Csizmadia, M. B. Davies, H. Deeg, M. Deleuil, L. Delrez, O. D.S. Demangeon, B. O. Demory, D. Ehrenreich, A. Erikson, M. Esposito, A. Fortier, M. Gillon, M. Güdel, K. Heng, K. G. Isaak, L. L. Kiss, J. Korth, J. Laskar, A. Lecavelier Des Etangs, M. Lendl, J. Livingston, C. Lovis, D. Magrin, P. F.L. Maxted, A. Muresan, V. Nascimbeni, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, S. Redfield, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, L. M. Serrano, A. E. Simon, A. M.S. Smith, M. Steller, Gy M. Szabó, N. Thomas, S. Udry, V. Van Eylen, V. Van Grootel, N. A. Walton
Abstract: Context. M-dwarf stars are the most common of potential exoplanet host stars in the Galaxy. It is therefore very important to understand planetary systems orbiting such stars and to determine the physical parameters of such planets with high precision. Also with the launch of the James Webb Space Telescope (JWST) the observation of atmospheric parameters of planets orbiting these stars has begun. It is therefore required to determine properties of potential targets. Aims. Two planets around the red dwarf TOI-776 were detected by TESS. The objective of our study was to use transit observations obtained by the CHEOPS space mission to improve the current precision of the planetary radii, as well as additional radial velocity (RV) data in order to improve mass estimates of the two planets. Using these quantities, we wanted to derive the bulk densities of those planets, improving the precision in earlier results, and use this information to put them in context of other exoplanetary systems involving very low mass stars. Methods. Utilizing new transit data from the CHEOPS satellite and its photometric telescope, we obtained very high precision planetary transit measurements. Interpretation of these provides updated planetary radii, along with other system parameters. A concurrent ESO large observing program using the high precision spectrograph HARPS has doubled the available radial velocity data. Calculating the power spectrum of a number of stellar activity indices we update the previously estimated stellar rotation period to a lower value. Results. The CHEOPS data provide precise transit depths of 909 and 1177 ppm translating into radii of R_b = 1.798_-0.077^+0.078 R_⊕ and R_c = 2.047_-0.078^+0.081 R_⊕, respectively. Our interpretation of the radial velocities and activity indicator time series data estimates a stellar rotation period for this early M dwarf of ~21.1 days. A further multi-dimensional Gaussian process approach confirm this new estimate. By performing a Skew-Normal (SN) fit onto the Cross Correlation Functions we extracted the RV data and the activity indicators to estimate the planetary masses, obtaining M_b = 5.0_-1.6^+1.6 M_⊕ and M_c = 6.9_-2.5^+2.6 M_⊕. Conclusions. We improve the precision in planetary radius for TOI-776 b and c by a factor of more than two. Our data and modelling give us parameters of both bodies consistent with mini-Neptunes, albeit with a relatively high density. The stellar activity of TOI-776 is found to have increased by a factor larger than 2 since the last set of observations.
Organisation(s): Department of Astrophysics
External organisation(s): Chalmers University of Technology, Leiden University, Österreichische Akademie der Wissenschaften (ÖAW), Universität Bern, University of Turin, Université de Genève, Aix-Marseille Université, Stockholm University, University of St. Andrews, University of Oxford, Lund Observatory, Thüringer Landessternwarte Tautenburg, 4Pharma Ltd, University of Cambridge, Instituto de Astrofísica de Andalucía (CSIC), University of Chicago, Universidade do Porto, Institute of Astrophysics of the Canary Islands, University of La Laguna, Spanish National Research Council (CSIC), Institute of Space Studies of Catalonia (IEEC), Admatis Ltd., European Space Astronomy Centre (ESA), University of Grenoble Alpes, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Université de Paris, Lund University, Université de Liège, University of Leicester, Science and Operations Department - Science Division (SCI-SC), Eötvös Loránd Research Network, Eötvös Loránd University Budapest, Université de recherche Paris Sciences et Lettres, Université Paris VI - Pierre-et-Marie-Curie, National Institutes of Natural Sciences (NINS), National Astronomical Observatory of Japan, University of Tokyo, Graduate University for Advanced Studies , Osservatorio Astronomico, Keele University, INAF-Osservatorio Astrofisico di Catania, University of Padova, University of Warwick, Eidgenössische Technische Hochschule Zürich, Technische Universität Berlin, Freie Universität Berlin (FU), Wesleyan University, University College London
Journal: Astronomy and Astrophysics
Volume: 684
No. of pages: 17
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202243838
Publication date: 04-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics, 103038 Space exploration
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/0672a1c7-adab-4068-b94b-b0bf70a55c6c

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