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Abstract The stellar companion to the weak-line T Tauri star DI Tau A was first discovered by the lunar occultation technique in 1989 and was subsequently confirmed by a speckle imaging observation in 1991. It has not been detected since, despite being targeted by five different studies that used a variety of methods and spanned more than 20 yr. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17 yr, new adaptive optics observations from Keck II, and a variety of other data from the literature, we derive a preliminary orbital solution for the system that effectively explains the detection and (almost all of the) non-detection history of DI Tau B. We estimate the dynamical masses of both components, finding that the large mass difference (q∼ 0.17) and long orbital period (≳35 yr) make the DI Tau system a noteworthy and valuable addition to studies of stellar evolution and pre-main-sequence models. With a long orbital period and a small flux ratio (f2/f1) between DI Tau A and B, additional measurements are needed for a better comparison between these observational results and pre-main-sequence models. Finally, we report an average surface magnetic field strength ( $\overline{B}$) for DI Tau A, of ∼0.55 kG, which is unusually low in the context of young active stars. 

Abstract Mature super-Earths and sub-Neptunes are predicted to be ≃ Jovian radius when younger than 10 Myr. Thus, we expect to find 5–15R_⊕planets around young stars even if their older counterparts harbor none. We report the discovery and validation of TOI 1227b, a 0.85 ± 0.05R_J(9.5R_⊕) planet transiting a very-low-mass star (0.170 ± 0.015M_⊙) every 27.4 days. TOI 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the Lower Centaurus Crux OB association, which we designate the Musca group. We derive an age of 11 ± 2 Myr for Musca, based on lithium, rotation, and the color–magnitude diagram of Musca members. The TESS data and ground-based follow-up show a deep (2.5%) transit. We use multiwavelength transit observations and radial velocities from the IGRINS spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5M_J. Because such large planets are exceptionally rare around mature low-mass stars, we suggest that TOI 1227b is still contracting and will eventually turn into one of the more common <5R_⊕planets.