Wolf 327b: A new member of the pack of ultra-short-period super-Earths around M dwarfs

Murgas, F.; Pallé, E.; Orell-Miquel, J.; Carleo, I.; Peña-Moñino, L.; Pérez-Torres, M.; Watkins, C. N.; Jeffers, S. V.; Azzaro, M.; Barkaoui, K.; Belinski, A. A.; Caballero, J. A.; Charbonneau, D.; Cheryasov, D. V.; Ciardi, D. R.; Collins, K. A.; Cortés-Contreras, M.; de Leon, J.; Duque-Arribas, C.; Enoc, G.; Esparza-Borges, E.; Fukui, A.; Geraldía-González, S.; Gilbert, E. A.; Hatzes, A. P.; Hayashi, Y.; Henning, Th.; Herrero, E.; Jenkins, J. M.; Lillo-Box, J.; Lodieu, N.; Lund, M. B.; Luque, R.; Montes, D.; Nagel, E.; Narita, N.; Parviainen, H.; Polanski, A. S.; Reffert, S.; Schlecker, M.; Schöfer, P.; Schwarz, R. P.; Schweitzer, A.; Seager, S.; Stassun, K. G.; Tabernero, H. M.; Terada, Y.; Twicken, J. D.; Vanaverbeke, S.; Winn, J. N.; Zambelli, R.; Amado, P. J.; Quirrenbach, A.; Reiners, A.; Ribas, I.
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Astronomy and Astrophysics

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Planets with orbital periods shorter than 1 day are rare and have formation histories that are not completely understood. Small (Rp < 2 R⊕) ultra-short-period (USP) planets are highly irradiated, probably have rocky compositions with high bulk densities, and are often found in multi-planet systems. Additionally, USP planets found around small stars are excellent candidates for characterization using present-day instrumentation. Of the current full sample of approximately 5500 confirmed exoplanets, only 130 are USP planets and around 40 have mass and radius measurements. Wolf 327 (TOI-5747) is an M dwarf (R* = 0.406 ± 0.015 R⊙, M* = 0.405 ± 0.019 M⊙, Teff = 3542 ± 70 K, and V = 13 mag) located at a distance d = 28.5 pc. NASA's planet hunter satellite, TESS, detected transits in this star with a period of 0.573 day (13.7 h) and with a transit depth of 818 ppm. Ground-based follow-up photometry, high resolution imaging, and radial velocity (RV) measurements taken with the CARMENES spectrograph confirm the presence of this new USP planet. Wolf 327b is a super-Earth with a radius of Rp = 1.24 ± 0.06 R⊕ and a mass of Mp = 2.53 ± 0.46 M⊕, yielding a bulk density of 7.24 ± 1.66 g cm−3 and thus suggesting a rocky composition. Owing to its close proximity to its host star (a = 0.01 au), Wolf 327b has an equilibrium temperature of 996 ± 22 K. This planet has a mass and radius similar to K2-229b, a planet with an inferred Mercury-like internal composition. Planet interior models suggest that Wolf 327b has a large iron core, a small rocky mantle, and a negligible (if any) H/He atmosphere.

Radial velocity measurement table is available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr ( or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/684/A83