2026-07-28T22:34:27Zivo://CDS.VizieR/J/ApJ/950/922025-10-01T06:29:29ZJ.ApJIVOARadial velocities and V-band phot. of DI TauThe 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 20yr. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17yr, 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 (>~35yr) 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 (\bar{B}) for DI Tau A, of ~0.55kG, which is unusually low in the context of young active stars.multiple-starsvisible-astronomyspectroscopyinfrared-astronomyradial-velocityphotometrystellar-astronomyobservational-astronomyexoplanet-astronomyinterdisciplinary-astronomyhttps://dc.g-vo.org/rr/q/lp/custom/CDS.VizieR/J/ApJ/950/92https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/950/922023ApJ...950...92Thttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/950/92Tang S.-Y.Stahl A.G.Prato L.Schaefer G.H.Johns-Krull C.M.,Skiff B.A.Beichman C.A.Uyama T.CDS2025https://cds.unistra.fr/vizier-org/licences_vizier.htmlCDS support team <cds-question@unistra.fr>DatasetAstroObjectsastronomy