A transit timing variation observed for the long-period extremely low density exoplanet HIP 41378f

Edward M. Bryant, Daniel Bayliss, Alexandre Santerne, Peter J. Wheatley, Valerio Nascimbeni, Elsa Ducrot, Artem Burdanov, Jack S. Acton, Douglas R. Alves, David R. Anderson, David J. Armstrong, Supachai Awiphan, Benjamin F. Cooke, Matthew R. Burleigh, Sarah L. Casewell, Laetitia Delrez, Brice-Olivier Demory, Philipp Eigmüller, Akihiko Fukui, Tianjun GanSamuel Gill, Michael Gillon, Michael R. Goad, Thiam-Guan Tan, Maximilian N. Günther, Bronwen Hardee, Beth A. Henderson, Emmanuel Jehin, James S. Jenkins, Molly Kosiarek, Monika Lendl, Maximiliano Moyano, Catriona A. Murray, Norio Narita, Prajwal Niraula, Caroline E. Odden, Enric Palle, Hannu Parviainen, Peter P. Pedersen, Francisco J. Pozuelos, Benjamin V. Rackham, Daniel Sebastian, Chris Stockdale, Rosanna H. Tilbrook, Samantha J. Thompson, Amaury H. M. J. Triaud, Stéphane Udry, Jose I. Vines, Richard G. West, Julien de Wit

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HIP 41378 f is a temperate 9.2 ± 0.1 R planet with period of 542.08 d and an extremely low density of 0.09 ± 0.02 g cm−3. It transits the bright star HIP 41378 (V=8.93),making it an exciting target for atmospheric characterization including transmission spectroscopy. HIP 41378 was monitored photometrically between the dates of 2019 November 19 and 28. We detected a transit of HIP 41378 f with NGTS, just the third transit ever detected for this planet, which confirms the orbital period. This is also the first ground-based detection of a transit of HIP 41378 f. Additional ground-based photometry was also obtained and used to constrain the time of the transit. The transit was measured to occur 1.50 h earlier than predicted. We use an analytic transit timing variation (TTV) model to show the observed TTV can be explained by interactions between HIP 41378 e and HIP 41378 f. Using our TTV model, we predict the epochs of future transits of HIP 41378 f, with derived transit centres of TC, 4 =2459 355.087+0.031−0.022
(2021 May) and TC, 5 =2459 897.078+0.114 −0.060 (2022 November).
Original languageEnglish
Pages (from-to)L45–L50
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Early online date16 Apr 2021
Publication statusPublished - Jun 2021


  • astro-ph.EP


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