An M dwarf accompanied by a close-in giant orbiter with SPECULOOS
Triaud, Amaury H. M. J.; Tamura, Motohide; Hirano, Teruyuki; Collins, Karen A.; Seager, Sara; Winn, Joshua N.; Caldwell, Douglas A.; Burgasser, Adam J.; Barkaoui, Khalid; Dransfield, Georgina; Fukui, Akihiko; Narita, Norio; Rackham, Benjamin V.; Gillon, Michaël; de Wit, Julien; Delrez, Laetitia; Ducrot, Elsa; Levine, Alan M.; Pozuelos, Francisco J.; Jehin, Emmanuël; Queloz, Didier; Kawauchi, Kiyoe; Pallé, Enric; Kotani, Takayuki; Benkhaldoun, Zouhair; Ikoma, Masahiro; Pedersen, Peter P.; Mori, Mayuko; Watanabe, Noriharu; Ghachoui, Mourad; Timmermans, Mathilde; Kagetani, Taiki; Hooton, Matthew J.; Sebastian, Daniel; Baycroft, Thomas; Davis, Yasmin T.; Demory, Brice-Oliver; Muñoz, Clàudia Jano; García, Lionel J.; Chew, Yilen Gómez Maqueo; Scutt, Owen J.; Thompson, Samantha; Zúñiga-Fernández, Sebastián
United Kingdom, Japan, Belgium, Spain, United States, Morocco, Switzerland, France, Mexico
Abstract
In the last decade, a dozen close-in giant planets have been discovered orbiting stars with spectral types ranging from M0 to M4, a mystery since known formation pathways do not predict the existence of such systems. Here, we confirm TOI-4860 b, a Jupiter-sized planet orbiting an M4.5 host, a star at the transition between fully and partially convective interiors. First identified with TESS data, we validate the transiting companion's planetary nature through multicolour photometry from the TRAPPIST-South/North, SPECULOOS, and MuSCAT3 facilities. Our analysis yields a radius of $0.76\pm 0.02~\rm R_{Jup}$ for the planet, a mass of $0.34~\rm M_\odot$ for the star, and an orbital period of $1.52~\rm d$. Using the newly commissioned SPIRIT InGaAs camera at the SPECULOOS-South Observatory, we collect infrared photometry in zYJ that spans the time of secondary eclipse. These observations do not detect a secondary eclipse, placing an upper limit on the brightness of the companion. The planetary nature of the companion is further confirmed through high-resolution spectroscopy obtained with the IRD spectrograph at Subaru Telescope, from which we measure a mass of $0.67\pm 0.14~\rm M_{Jup}$. Based on its overall density, TOI-4860 b appears to be rich in heavy elements, like its host star.