TOI-4860 b, a short-period giant planet transiting an M3.5 dwarf

Almenara, J. M.; Bonfils, X.; Bryant, E. M.; Jordán, A.; Hébrard, G.; Martioli, E.; Correia, A. C. M.; Astudillo-Defru, N.; Cadieux, C.; Arnold, L.; Artigau, É.; Bakos, G. Á.; Barros, S. C. C.; Bayliss, D.; Bouchy, F.; Boué, G.; Brahm, R.; Carmona, A.; Charbonneau, D.; Ciardi, D. R.; Cloutier, R.; Cointepas, M.; Cook, N. J.; Cowan, N. B.; Delfosse, X.; Dias do Nascimento, J.; Donati, J. -F.; Doyon, R.; Forveille, T.; Fouqué, P.; Gaidos, E.; Gilbert, E. A.; Gomes da Silva, J.; Hartman, J. D.; Hesse, K.; Hobson, M. J.; Jenkins, J. M.; Kiefer, F.; Kostov, V. B.; Laskar, J.; Lendl, M.; L'Heureux, A.; Martins, J. H. C.; Menou, K.; Moutou, C.; Murgas, F.; Polanski, A. S.; Rapetti, D.; Sedaghati, E.; Shang, H.
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Astronomy and Astrophysics

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We report the discovery and characterisation of a giant transiting planet orbiting a nearby M3.5V dwarf (d = 80.4pc, G = 15.1 mag, K=11.2mag, R* = 0.358 ± 0.015 R⊙, M* = 0.340 ± 0.009 M⊙). Using the photometric time series from TESS sectors 10, 36, 46, and 63 and near-infrared spectrophotometry from ExTrA, we measured a planetary radius of 0.77 ± 0.03 RJ and an orbital period of 1.52 days. With high-resolution spectroscopy taken by the CFHT/SPIRou and ESO/ESPRESSO spectrographs, we refined the host star parameters ([Fe/H] = 0.27 ± 0.12) and measured the mass of the planet (0.273 ± 0.006 MJ). Based on these measurements, TOI-4860 b joins the small set of massive planets (>80 ME) found around mid to late M dwarfs (<0.4 R⊙), providing both an interesting challenge to planet formation theory and a favourable target for further atmospheric studies with transmission spectroscopy. We identified an additional signal in the radial velocity data that we attribute to an eccentric planet candidate (e = 0.66 ± 0.09) with an orbital period of 427 ± 7 days and a minimum mass of 1.66 ± 0.26 MJ, but additional data would be needed to confirm this.