TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HD 15906

Author(s): A. Tuson, D. Queloz, H. P. Osborn, T. G. Wilson, M. J. Hooton, M. Beck, M. Lendl, G. Olofsson, A. Fortier, A. Bonfanti, A. Brandeker, L. A. Buchhave, A. Collier Cameron, D. R. Ciardi, K. A. Collins, D. Gandolfi, Z. Garai, S. Giacalone, J. Gomes da Silva, S. B. Howell, J. A. Patel, C. M. Persson, L. M. Serrano, S. G. Sousa, S. Ulmer-Moll, A. Vanderburg, C. Ziegler, Y. Alibert, R. Alonso, G. Anglada, T. Bárczy, D. Barrado Navascues, S. C.C. Barros, W. Baumjohann, T. Beck, W. Benz, N. Billot, X. Bonfils, L. Borsato, C. Broeg, J. Cabrera, S. Charnoz, D. M. Conti, Sz Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, L. Delrez, O. D.S. Demangeon, B. O. Demory, D. Dragomir, C. D. Dressing, D. Ehrenreich, A. Erikson, Z. Essack, J. Farinato, L. Fossati, M. Fridlund, E. Furlan, H. Gill, M. Gillon, C. L. Gnilka, E. Gonzales, M. Güdel, M. N. Günther, S. Hoyer, K. G. Isaak, J. M. Jenkins, L. L. Kiss, J. Laskar, D. W. Latham, N. Law, A. Lecavelier des Etangs, G. Lo Curto, C. Lovis, R. Luque, D. Magrin, A. W. Mann, P. F.L. Maxted, M. Mayor, S. McDermott, M. Mecina, C. Mordasini, A. Mortier, V. Nascimbeni, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, T. Pritchard, R. Ragazzoni, N. Rando, F. Ratti, H. Rauer, I. Ribas, G. R. Ricker, M. Rieder, N. C. Santos, A. B. Savel, G. Scandariato, R. P. Schwarz, S. Seager, D. Ségransan, A. Shporer, A. E. Simon, A. M.S. Smith, M. Steller, C. Stockdale, Gy M. Szabó, N. Thomas, G. Torres, R. Tronsgaard, S. Udry, B. Ulmer, V. Van Grootel, R. Vanderspek, J. Venturini, N. A. Walton, J. N. Winn, B. Wohler
Abstract: We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by ∼ 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 ± 0.08 R and a period of 10.924709 ± 0.000032 d, whilst HD 15906 c has a radius of 2.93⁺₋₀⁰₀₆⁰⁷ R and a period of 21.583298⁺₋₀⁰₀₀₀₀₅₅⁰⁰⁰⁰⁵² d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 ± 13 K and 532 ± 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm (700 K) sub-Neptune sized planets transiting a bright star (G ≤ 10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution.
Organisation(s): Department of Astrophysics
External organisation(s): University of Cambridge, Eidgenössische Technische Hochschule Zürich, Universität Bern, Massachusetts Institute of Technology, University of St. Andrews, Université de Genève, Stockholm University, Österreichische Akademie der Wissenschaften (ÖAW), Technical University of Denmark (DTU), National Aeronautics & Space Administration (NASA), Harvard-Smithsonian Center for Astrophysics, University of Turin, Slovak Academy of Sciences (SAS), Slovenian Academy of Sciences and Arts, Eötvös Loránd University Budapest, University of California, Berkeley, Universidade do Porto, Chalmers University of Technology, Stephen F. Austin State University, Institute of Astrophysics of the Canary Islands, University of La Laguna, Universitat Autònoma de Barcelona , Spanish National Research Council (CSIC), Institute of Space Studies of Catalonia (IEEC), Admatis Ltd., European Space Astronomy Centre (ESA), University of Grenoble Alpes, Osservatorio Astronomico, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Université de Paris, American Association of Variable Star Observers (AAVSO), INAF-Osservatorio Astrofisico di Torino, Lund University, Aix-Marseille Université, Université de Liège, University of New Mexico, Leiden University, University of California, Santa Cruz, Science and Operations Department - Science Division (SCI-SC), Eötvös Loránd Research Network, Université de recherche Paris Sciences et Lettres, University of North Carolina at Chapel Hill, Université Paris VI - Pierre-et-Marie-Curie, European Southern Observatory (Germany), University of Chicago, Keele University, Proto-Logic LLC, University of Birmingham, INAF-Osservatorio Astrofisico di Catania, University of Padova, University of Warwick, Technische Universität Berlin, Freie Universität Berlin (FU), University of Maryland, College Park, Hazelwood Observatory, Princeton University, SETI Institute
Journal: Monthly Notices of the Royal Astronomical Society
Volume: 523
Pages: 3090-3118
No. of pages: 29
ISSN: 0035-8711
DOI: https://doi.org/10.1093/mnras/stad1369
Publication date: 08-2023
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/4dcee8a6-0039-4008-ab29-f84bbb88a105

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