Three short-period Earth-sized planets around M dwarfs discovered by TESS: TOI-5720 b, TOI-6008 b, and TOI-6086 b

One of the main goals of the NASA Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of Earth-like planets around nearby M-dwarf stars. We present the discovery and validation of three new short-period Earth-sized planets orbiting nearby M dwarfs: TOI-5720 b, TOI-6008 b, and TOI-6086 b. We combined TESS data, ground-based multicolor light curves, ground-based optical and near-infrared spectroscopy, and Subaru/IRD radial velocity data to validate the planetary candidates and constrain the physical parameters of the systems. In addition, we used archival images, high-resolution imaging, and statistical validation techniques to support the planetary validation. TOI-5720 b is an Earth-sized planet with a radius of R_p = 1.09 ± 0.07 R_⊕. It orbits a nearby (36 pc) M 2.5 host with an orbital period of P = 1.4344555 ± 0.0000036 days. It has an equilibrium temperature of T_eq = 708 ± 19 K (assuming a null albedo) and an incident flux of S_p = 41.7 ± 4.5 S_⊕. TOI-6008 b is a short-period planet of P = 0.8574347 ± 0.0000424 day. It has a radius of R_p = 1.03 ± 0.05 R_⊕, an equilibrium temperature of T_eq = 707 ± 19 K, and an incident flux of S_p = 41.5 ± 4.5 S_⊕. The host star (TOI-6008) is a nearby (23 pc) M 5 with an effective temperature of T_eff = 3075 ± 75 K. Based on the radial velocity measurements collected with Subaru/IRD, we set a 3σ upper limit of M_p < 4 M_⊕, thus ruling out a star or brown dwarf as the transiting companion. TOI-6086 b orbits its nearby (32 pc) M 3 host star (T_eff = 3200 ± 75 K) every 1.3888725 ± 0.0000827 days and has a radius of R_p = 1.18 ± 0.07 R_⊕, an equilibrium temperature of T_eq = 634 ± 16 K, and an incident flux of S_p = 26.8 ± 2.7 S_⊕. Additional high-precision radial velocity measurements are needed to derive the planetary masses and bulk densities and to search for additional planets in the systems. Moreover, short-period Earth-sized planets orbiting around nearby M dwarfs are suitable targets for an atmospheric characterization with the James Webb Space Telescope through transmission and emission spectroscopy and phase-curve photometry.