Wolf 327b: A new member of the pack of ultra-short-period super-Earths around M dwarfs
F. Murgas, Ε. Πάλλη, J. Orell-Miquel, I. Carleo, L. Peña-Moñino, M. Á. Pérez-Torres, Cristilyn N. Watkins, S. V. Jeffers, M. Azzaro, Khalid Barkaoui, A. Belinski, J. A. Caballero, D. Charbonneau, D. Cheryasov, David R. Ciardi, Karen A. Collins, M. Cortés‐Contreras, Jerome de Leon, C. Duque-Arribas, G. Enoc, E. Esparza-Borges, Akihiko Fukui, S. Geraldía-González, Emily A. Gilbert, A. P. Hatzes, Yoshikatsu Hayashi, Th. Henning, E. Herrero, Jon M. Jenkins, J. Lillo-Box, N. Lodieu, Michael B. Lund, R. Luque, D. Montes, E. Nagel, Norio Narita, H. Parviainen, Alex S. Polanski, S. Reffert, Martin Schlecker, P. Schöfer, Richard P. Schwarz, A. Schweitzer, Sara Seager, Keivan G. Stassun, H. M. Tabernero, Yuka Terada, Joseph D. Twicken, S. Vanaverbeke, Joshua N. Winn, Roberto Zambelli, P. J. Amado, A. Quirrenbach, A. Reiners, I. Ribas
Abstract
Planets with orbital periods shorter than 1 day are rare and have formation histories that are not completely understood. Small ( R p < 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 ⊙ , T eff = 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 R p = 1.24 ± 0.06 R ⊕ and a mass of M p = 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.