Masses, revised radii, and a third planet candidate in the 'Inverted' planetary system around TOI-1266

Cloutier, Ryan; Greklek-McKeon, Michael; Wurmser, Serena; Cherubim, Collin; Gillis, Erik; Vanderburg, Andrew; Hadden, Sam; Cadieux, Charles; Artigau, Étienne; Vissapragada, Shreyas; Mortier, Annelies; López-Morales, Mercedes; Latham, David W.; Knutson, Heather; Haywood, Raphaëlle D.; Pallé, Enric; Doyon, René; Cook, Neil; Andreuzzi, Gloria; Cecconi, Massimo; Cosentino, Rosario; Ghedina, Adriano; Harutyunyan, Avet; Pinamonti, Matteo; Stalport, Manu; Damasso, Mario; Rescigno, Federica; Wilson, Thomas G.; Buchhave, Lars A.; Charbonneau, David; Cameron, Andrew Collier; Dumusque, Xavier; Lovis, Christophe; Mayor, Michel; Molinari, Emilio; Pepe, Francesco; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, Chris A.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

Advertised on:
1
2024
Number of authors
43
IAC number of authors
1
Citations
3
Refereed citations
2
Description
Is the population of close-in planets orbiting M dwarfs sculpted by thermally driven escape or is it a direct outcome of the planet formation process? A number of recent empirical results strongly suggest the latter. However, the unique architecture of the TOI-1266 system presents a challenge to models of planet formation and atmospheric escape given its seemingly 'inverted' architecture of a large sub-Neptune (Pb = 10.9 d, $R_{p,b}=2.62\pm 0.11\, \mathrm{R}_{\oplus }$) orbiting interior to that of the system's smaller planet (Pc = 18.8 d, $R_{p,c}=2.13\pm 0.12\, \mathrm{R}_{\oplus }$). Here, we present revised planetary radii based on new TESS and diffuser-assisted ground-based transit observations, and characterize both planetary masses using a set of 145 radial velocity measurements from HARPS-N ($M_{p,b}=4.23\pm 0.69\, \mathrm{M}_{\oplus }, M_{p,c}=2.88\pm 0.80\, \mathrm{M}_{\oplus }$). Our analysis also reveals a third planet candidate (Pd = 32.3 d, $M_{p,d}\sin {i} = 4.59^{+0.96}_{-0.94}\, \mathrm{M}_{\oplus }$), which if real, would form a chain of near 5:3 period ratios, although the system is likely not in a mean motion resonance. Our results indicate that TOI-1266 b and c are among the lowest density sub-Neptunes around M dwarfs and likely exhibit distinct bulk compositions of a gas-enveloped terrestrial (Xenv,b = 5.5 ± 0.7 per cent) and a water-rich world (WMFc = 59 ± 14 per cent), which is supported by hydrodynamic escape models. If distinct bulk compositions are confirmed through atmospheric characterization, the system's unique architecture would represent an interesting test case of inside-out sub-Neptune formation at pebble traps.