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arXiv · 2210.10909

TOI-3884 b: A rare 6-R$_{\oplus}$ planet that transits a low-mass star with a giant and likely polar spot

J. M. Almenara·X. Bonfils·T. Forveille·N. Astudillo-Defru·D. R. Ciardi·R. P. Schwarz·K. A. Collins·M. Cointepas·M. B. Lund·F. Bouchy·D. Charbonneau·R. F. Díaz·X. Delfosse·R. C. Kidwell·M. Kunimoto·D. W. Latham·J. J. Lissauer·F. Murgas·G. Ricker·S. Seager·M. Vezie·D. Watanabe
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Abstract

The Transiting Exoplanet Survey Satellite mission identified a deep and asymmetric transit-like signal with a periodicity of 4.5 days orbiting the M4 dwarf star TOI-3884. The signal has been confirmed by follow-up observations collected by the ExTrA facility and Las Cumbres Observatory Global Telescope, which reveal that the transit is chromatic. The light curves are well modelled by a host star having a large polar spot transited by a 6-R$_{\oplus}$ planet. We validate the planet with seeing-limited photometry, high-resolution imaging, and radial velocities. TOI-3884 b, with a radius of $6.00 \pm 0.18$ R$_{\oplus}$, is the first sub-Saturn planet transiting a mid-M dwarf. Owing to the host star's brightness and small size, it has one of the largest transmission spectroscopy metrics for this planet size and becomes a top target for atmospheric characterisation with the James Webb Space Telescope and ground-based telescopes.

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J. M. Almenara, X. Bonfils, T. Forveille, N. Astudillo-Defru, D. R. Ciardi, R. P. Schwarz, K. A. Collins, M. Cointepas, M. B. Lund, F. Bouchy, D. Charbonneau, R. F. Díaz, X. Delfosse, R. C. Kidwell, M. Kunimoto, D. W. Latham, J. J. Lissauer, F. Murgas, G. Ricker, S. Seager, M. Vezie, D. Watanabe. 2022-10-19. TOI-3884 b: A rare 6-R$_{\oplus}$ planet that transits a low-mass star with a giant and likely polar spot. https://doi.org/10.1051/0004-6361/202244791

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