Context. The NASA space telescope TESS is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. Aims. We aim to validate and characterize the new sub-Neptune sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 ± 0.02 pc, T e f f = 3373 ± 108 K) with an orbital period of 7.852 days. Methods. We use TESS data, ground-based multi-color photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01 and estimate the stellar and planetary parameters. We also conduct highresolution transmission spectroscopy to search for helium in its atmosphere. Results. We confirmed that TOI-2136.01 (now named as TOI-2136b) is a bona fide planet with a planetary radius of R p = 2.2 ± 0.07 R ⊕ and a mass of M p = 4.7 +3.1 −2.6 M ⊕ . We also search for helium 10830 Å absorption lines and place an upper limit on the equivalent width of < 7.8 mÅ (95% confidence) and on the absorption signal of < 1.44 % (95% confidence). Conclusions. TOI-2136b is a sub-Neptune transiting a nearby and bright star (J=10.8) and is a potential hycean planet, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets.

Context. Exoplanets with orbital periods of less than one day are know as Ultra-short period (USP) planets. They are relatively rare products of planetary formation and evolution processes, but especially favourable to current planet detection methods. At the time of writing, 120 USP planets have already been confirmed. Aims. We aim to confirm the planetary nature of two new transiting planet candidates announced by the NASA's Transiting Exoplanet Survey Satellite (TESS), registered as TESS Objects of Interest (TOIs) TOI-1442.01 and TOI-2445.01. Methods. We use the TESS data, ground-based photometric light-curves and Subaru/IRD spectrograph radial velocity (RV) measurements to validate both planetary candidates and to establish their physical properties. Results. TOI-1442 b is a hot super-Earth with an orbital period of P = 0.4090682 ± 0.0000004 d, a radius of R p = 1.27 +0.50 −0.44 R ⊕ , equilibrium temperature of T p,eq = 1359 +49−42 K, and a mass M p < 18M ⊕ at 3σ. TOI-2445 b is also a hot super-Earth/mini-Neptune with an orbital period of P = 0.3711286 ± 0.0000004 d, a radius of R p = 1.52 +1.20 −0.26 R ⊕ , equilibrium temperature of T p,eq = 1332 +61 −57 K, and a mass M p < 38M ⊕ at 3σ. Their physical properties align with current empirical trends and formation theories of USP planets. More RV measurements will be useful to constrain the planetary masses and mean densities, as well as the predicted presence of outer planetary companions.