# An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685

Bluhm, P.; Pallé, E.; Molaverdikhani, K.; Kemmer, J.; Hatzes, A. P.; Kossakowski, D.; Stock, S.; Caballero, J. A.; Lillo-Box, J.; Béjar, V. J. S.; Soto, M. G.; Amado, P. J.; Brown, P.; Cadieux, C.; Cloutier, R.; Collins, K. A.; Collins, K. I.; Cortés-Contreras, M.; Doyon, R.; Dreizler, S.; Espinoza, N.; Fukui, A.; González-Álvarez, E.; Henning, Th.; Horne, K.; Jeffers, S. V.; Jenkins, J. M.; Jensen, E. L. N.; Kaminski, A.; Kielkopf, J. F.; Kusakabe, N.; Kürster, M.; Lafrenière, D.; Luque, R.; Murgas, F.; Montes, D.; Morales, J. C.; Narita, N.; Passegger, V. M.; Quirrenbach, A.; Schöfer, P.; Reffert, S.; Reiners, A.; Ribas, I.; Ricker, G. R.; Seager, S.; Schweitzer, A.; Schwarz, R. P.; Tamura, M.; Trifonov, T.; Vanderspek, R.; Winn, J.; Zechmeister, M.; Zapatero Osorio, M. R.
Bibliographical reference

Astronomy and Astrophysics

6
2021
Description
Dynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of Pb = 0.6691403−0.0000021+0.0000023 d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of Mb = 3.78−0.63+0.63 M⊕, a radius of Rb = 1.70−0.07+0.07 R⊕, which together result in a bulk density of ρb = 4.21−0.82+0.95 g cm−3, and an equilibrium temperature of Teq = 1069−16+16 K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 [c], which has an orbital period of Pc = 9.02−0.12+0.10 d.
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