A pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 characterized with CHEOPS
Authors: Wilson Thomas G , Goffo Elisa , Alibert Yann , Gandolfi Davide , Bonfanti Andrea , Persson Carina M , Collier Cameron Andrew , Fridlund Malcolm , Fossati Luca , Korth Judith , Benz Willy , Deline Adrien , Florén Hans-Gustav , Guterman Pascal , Adibekyan Vardan , Hooton Matthew J , Hoyer Sergio , Leleu Adrien , Mustill Alexander James , Salmon Sébastien , Sousa Sérgio G , Suarez Olga , Abe Lyu , Agabi Abdelkrim , Alonso Roi , Anglada Guillem , Asquier Joel , Bárczy Tamas , Barrado Navascues David , Barros Susana C C , Baumjohann Wolfgang , Beck Mathias , Beck Thomas , Billot Nicolas , Bonfils Xavier , Brandeker Alexis , Broeg Christopher , Bryant Edward M , Burleigh Matthew R , Buttu Marco , Cabrera Juan , Charnoz Sébastien , Ciardi David R , Cloutier Ryan , Cochran William D , Collins Karen A , Colón Knicole D , Crouzet Nicolas , Csizmadia Szilard , Davies Melvyn B , Deleuil Magali , Delrez Laetitia , Demangeon Olivier , Demory Brice-Olivier , Dragomir Diana , Dransfield Georgina , Ehrenreich David , Erikson Anders , Fortier Andrea , Gan Tianjun , Gill Samuel , Gillon Michaël , Gnilka Crystal L , Grieves Nolan , Grziwa Sascha , Güdel Manuel , Guillot Tristan , Haldemann Jonas , Heng Kevin , Horne Keith , Howell Steve B , Isaak Kate G , Jenkins Jon M , Jensen Eric L N , Kiss Laszlo , Lacedelli Gaia , Lam Kristine , Laskar Jacques , Latham David W , Lecavelier des Etangs Alain , Lendl Monika , Lester Kathryn V , Levine Alan M , Livingston John , Lovis Christophe , Luque Rafael , Magrin Demetrio , Marie-Sainte Wenceslas , Maxted Pierre F L , Mayo Andrew W , McLean Brian , Mecina Marko , Mékarnia Djamel , Nascimbeni Valerio , Nielsen Louise D , Olofsson Göran , Osborn Hugh P , Osborne Hannah L M , Ottensamer Roland , Pagano Isabella , Pallé Enric , Peter Gisbert , Piotto Giampaolo , Pollacco Don , Queloz Didier , Ragazzoni Roberto , Rando Nicola , Rauer Heike , Redfield Seth , Ribas Ignasi , Ricker George R , Rieder Martin , Santos Nuno C , Scandariato Gaetano , Schmider François-Xavier , Schwarz Richard P , Scott Nicholas J , Seager Sara , Ségransan Damien , Serrano Luisa Maria , Simon Attila E , Smith Alexis M S , Steller Manfred , Stockdale Chris , Szabó Gyula , Thomas Nicolas , Ting Eric B , Triaud Amaury H M J , Udry Stéphane , Van Eylen Vincent , Van Grootel Valérie , Vanderspek Roland K , Viotto Valentina , Walton Nicholas , Winn Joshua N 
Published: January 2022

ABSTRACT
We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine $T_{\rm eff, \star }=4734\pm 67\,\mathrm{ K}$, $R_{\star }=0.726\pm 0.007\, \mathrm{ R}_{\odot }$, and $M_{\star }=0.748\pm 0.032\, \mathrm{ M}_{\odot }$. We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 R⊕, and a mass of $M_{\rm b} = 13.5_{-1.8}^{+1.7}$ M⊕, whilst TOI-1064 c has an orbital period of $P_{\rm c} = 12.22657^{+0.00005}_{-0.00004}$ d, a radius of Rc = 2.65 ± 0.04 R⊕, and a 3σ upper mass limit of 8.5 M⊕. From the high-precision photometry we obtain radius uncertainties of ∼1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass–radius space, and it allow us to identify a trend in bulk density–stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.