Bibcode
                                    
                            Osborn, H. P.; Nowak, G.; Hébrard, G.; Masseron, T.; Lillo-Box, J.; Pallé, E.; Bekkelien, A.; Florén, H. -G.; Guterman, P.; Simon, A. E.; Adibekyan, V.; Bieryla, A.; Borsato, L.; Brandeker, A.; Ciardi, D. R.; Collier Cameron, A.; Collins, K. A.; Egger, J. A.; Gandolfi, D.; Hooton, M. J.; Latham, D. W.; Lendl, M.; Matthews, E. C.; Tuson, A.; Ulmer-Moll, S.; Vanderburg, A.; Wilson, T. G.; Ziegler, C.; Alibert, Y.; Alonso, R.; Anglada, G.; Arnold, L.; Asquier, J.; Barrado y Navascues, D.; Baumjohann, W.; Beck, T.; Belinski, A. A.; Benz, W.; Biondi, F.; Boisse, I.; Bonfils, X.; Broeg, C.; Buchhave, L. A.; Bárczy, T.; Barros, S. C. C.; Cabrera, J.; Cardona Guillen, C.; Carleo, I.; Castro-González, A.; Charnoz, S.; Christiansen, J.; Cortes-Zuleta, P.; Csizmadia, S.; Dalal, S.; Davies, M. B.; Deleuil, M.; Delfosse, X.; Delrez, L.; Demory, B. -O.; Dunlavey, A. B.; Ehrenreich, D.; Erikson, A.; Fernandes, R. B.; Fortier, A.; Forveille, T.; Fossati, L.; Fridlund, M.; Gillon, M.; Goeke, R. F.; Goliguzova, M. V.; Gonzales, E. J.; Günther, M. N.; Güdel, M.; Heidari, N.; Henze, C. E.; Howell, S.; Hoyer, S.; Frey, J. I.; Isaak, K. G.; Jenkins, J. M.; Kiefer, F.; Kiss, L.; Korth, J.; Maxted, P. F. L.; Laskar, J.; Lecavelier des Etangs, A.; Lovis, C.; Lund, M. B.; Luque, R.; Magrin, D.; Almenara, J. M.; Martioli, E.; Mecina, M.; Medina, J. V.; Moldovan, D.; Morales-Calderón, M.; Morello, G.; Moutou, C.; Murgas, F.; Jensen, E. L. N. et al.
    Bibliographical reference
                                    Monthly Notices of the Royal Astronomical Society
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                        8
            
                        2023
            
  Citations
                                    20
                            Refereed citations
                                    18
                            Description
                                    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 $6.8\pm 1.4~{{\ \rm per\ cent}}$ 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 ($0.08^{+0.12}_{-0.05} M_\odot$) orbiting at $26.0^{+19.0}_{-11.0}$ 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 (Teq < 750 K) sub-Neptunes.
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