2017ApJ...845..161A

We present high-resolution, spatially resolved, near-infrared spectroscopy and imaging of the two components of DF Tau, a young, low-mass, visual binary in the Taurus star-forming region. With these data, we provide a more precise orbital solution for the system, determine component spectral types, radial velocity, veiling and vsini values, and construct individual spectral energy distributions. We estimate the masses of both stars to be ∼0.6 M_☉. We find markedly different circumstellar properties for DF Tau A and B: evidence for a disk, such as near-infrared excess and accretion signatures, is clearly present for the primary, while it is absent for the secondary. Additionally, the vsini and rotation period measurements show that the secondary is rotating significantly more rapidly than the primary. We interpret these results in the framework of disk-locking and argue that DF Tau A is an example of disk-modulated rotation in a young system. The DF Tau system raises fundamental questions about our assumptions of universal disk formation and evolution.