Two warm Neptunes transiting HIP 9618 revealed by TESS and Cheops

Author(s)

H. P. Osborn, G. Nowak, G. Hébrard, T. Masseron, J. Lillo-Box, E. Pallé, A. Bekkelien, H. G. Florén, P. Guterman, A. E. Simon, V. Adibekyan, A. Bieryla, L. Borsato, A. Brandeker, D. R. Ciardi, A. Collier Cameron, K. A. Collins, J. A. Egger, D. Gandolfi, M. J. Hooton, D. W. Latham, M. Lendl, E. C. Matthews, A. Tuson, S. Ulmer-Moll, A. Vanderburg, T. G. Wilson, C. Ziegler, Y. Alibert, R. Alonso, G. Anglada, L. Arnold, J. Asquier, D. Barrado y Navascues, W. Baumjohann, T. Beck, A. A. Belinski, W. Benz, F. Biondi, I. Boisse, X. Bonfils, C. Broeg, L. A. Buchhave, T. Bárczy, S. C.C. Barros, J. Cabrera, C. Cardona Guillen, I. Carleo, A. Castro-González, S. Charnoz, J. Christiansen, P. Cortes-Zuleta, S. Csizmadia, S. Dalal, M. B. Davies, M. Deleuil, X. Delfosse, L. Delrez, B. O. Demory, A. B. Dunlavey, D. Ehrenreich, A. Erikson, R. B. Fernandes, A. Fortier, T. Forveille, L. Fossati, M. Fridlund, M. Gillon, R. F. Goeke, M. V. Goliguzova, E. J. Gonzales, M. N. Günther, M. Güdel, N. Heidari, C. E. Henze, S. Howell, S. Hoyer, J. I. Frey, K. G. Isaak, J. M. Jenkins, F. Kiefer, L. Kiss, J. Korth, P. F.L. Maxted, J. Laskar, A. Lecavelier des Etangs, C. Lovis, M. B. Lund, R. Luque, D. Magrin, J. M. Almenara, E. Martioli, M. Mecina, J. V. Medina, D. Moldovan, M. Morales-Calderón, G. Morello, C. Moutou, F. Murgas, E. L.N. Jensen, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, G. Ricker, O. D.S. Demangeon, A. M.S. Smith, N. Santos, G. Scandariato, S. Seager, S. G. Sousa, M. Steller, G. M. Szabó, D. Ségransan, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, R. Vanderspek, N. Walton, J. N. Winn

Abstract

HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of 3.9 ± 0.044 R (HIP 9618 b) and 3.343 ± 0.039 R (HIP 9618 c). While the 20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M for HIP 9618 b, which, according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of <18M. Follow-up and archival RV measurements also reveal a clear long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion (0.08⁺₋₀⁰₀₅¹²M_☉) orbiting at 26.0⁺₋₁₁¹⁹₀⁰ au. This detection makes HIP 9618 one of only five bright (K < 8 mag) transiting multiplanet systems known to host a planet with P > 50 d, opening the door for the atmospheric characterization of warm (T_eq < 750 K) sub-Neptunes.

Organisation(s)

Department of Astrophysics

External organisation(s)

Universität Bern, Massachusetts Institute of Technology, Nicolaus Copernicus University, Institute of Astrophysics of the Canary Islands, University of La Laguna, Université Paris VI - Pierre-et-Marie-Curie, European Space Astronomy Centre (ESA), Université de Genève, Stockholm University, Aix-Marseille Université, Universidade do Porto, Harvard-Smithsonian Center for Astrophysics, Osservatorio Astronomico, National Aeronautics & Space Administration (NASA), University of St. Andrews, Università degli Studi di Torino, University of Cambridge, Max-Planck-Institut für Astronomie, Stephen F. Austin State University, Universitat Autònoma de Barcelona , Spanish National Research Council (CSIC), Institute of Space Studies of Catalonia (IEEC), Centre National De La Recherche Scientifique (CNRS), Science and Operations Department - Science Division (SCI-SC), Österreichische Akademie der Wissenschaften (ÖAW), Anuchin Research Institute and Museum of Anthropology, Max-Planck-Institut für extraterrestrische Physik, University of Grenoble Alpes, Technical University of Denmark (DTU), Admatis Ltd., Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Université de Paris, Lund University, Université de Liège, University of Arizona, Leiden University, Chalmers University of Technology, University of California, Santa Cruz, Université de recherche Paris Sciences et Lettres, Eötvös Loránd Research Network, Eötvös Loránd University Budapest, Lund Observatory, Keele University, University of Chicago, Laboratório Nacional de Astrofísica, Space Telescope Science Institute, Google, University of Toulouse, Swarthmore College, INAF-Osservatorio Astrofisico di Catania, University of Padova, University of Warwick, Eidgenössische Technische Hochschule Zürich, Technische Universität Berlin, Freie Universität Berlin (FU), Princeton University

Journal

Monthly Notices of the Royal Astronomical Society

Volume

523

Pages

3069-3089

No. of pages

21

ISSN

0035-8711

DOI

https://doi.org/10.1093/mnras/stad1319

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/58be0431-c8bd-478f-ae63-878de539beb2