2026ApJ...997..323G

We have acquired high-resolution optical spectroscopy for a sample of T Tauri stars (TTSs) in open clusters using Hydra on the WIYN 3.5 m telescope, and present projected rotational velocities (v sin i values) for 54 stars in IC 5070 and 99 stars in IC 348. We combine these with published values for stellar temperature, luminosity, rotation period, circumstellar disk status, and binarity; we are predominantly interested in how the last two factors may affect the rotation speeds of the stars. We find evidence to support theories that interaction with circumstellar disks may slow the rotation of TTSs compared to class III stars in both clusters. We also identify a higher fraction of slow-rotating class III stars in IC 348 compared to other clusters; we suggest that some fraction of these may be stars that recently lost their disks. We find that a higher fraction of binary stars are rapid rotators compared to single stars, although not to a statistically significant degree. We also combine our v sin i measurements with rotation periods to estimate projected stellar radii, which we compare to predictions from stellar evolution models using a maximum-likelihood method. We continue to show that models with increasing starspot coverage reduce radius inflation and align better with published age estimates than models without starspots.