Toby Rodel, Soléne Ulmer-Moll, S Gill, C A Watson, Yoshi Nike Emilia Eschen, Alix Violet Freckelton, A Mortier, Karen A Collins, Diana Dragomir, Z Essack, Brett Skinner, Niamh Mallaghan, P J Wheatley, David R. Anderson, Ioannis Apergis, Khalid Barkaoui, Matthew P. Battley, Daniel Bayliss, François Bouchy, Edward M. Bryant, M. R. Burleigh, Benjamin M J Cadell, Samuel Carlier, Yann Carteret, Sarah L Casewell, Alastair B Claringbold, Jean C Costes, Benjamin D R Davies, Lauren Doyle, Phil Evans, Jorge Fernández Fernández, E. Fontanet, Edward Gillen, Michael R Goad, G. M. Harvey, Faith Hawthorn, K. Hobbs, Melissa Hobson, Giovanni Isopi, J S Jenkins, Alicia Kendall, David Kipping, Monika Lendl, F. Mallia, Christopher Mann, J McCormac, Ernst de Mooij, M Moyano, A. Nigioni, Mohammad Odeh, V. M. Passegger, S Saha, Richard P Schwarz, Amber Sedgley, Avi Shporer, Abderahmane Soubkiou, Stéphane Udry, Dimitri Veras, Jean P Vignes, Steven Villanueva, J I Vines, R. G. West, T G Wilson, Hannah L. Worters, Mitchell E. Young, Aldo Zapparata
ABSTRACT We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081\pm 0.047$ RJ and a mass of $4.77_{-0.37}^{+0.39}$ MJ on a long-period ($180.52797\pm 0.00036$ d), moderately eccentric (e = $0.3086\pm 0.010$) orbit transiting a bright (V=$10.230\pm 0.020$ mag) metal rich ([Fe/H]=$0.33\pm 0.09$ ‘dex’) F6V–F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of 180.5 d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $457\pm 11$ K, NGTS-38 b joins a small but growing population of well characterized transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b’s bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.