Ruprecht 147 members & rot. data for 5 other cl.

These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure P_rot_ for 58 dwarf members of the 2.7Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries.

Combined with the Kepler P_rot_ data for the approximately coeval cluster NGC6819 (30 stars with M*>0.85M_{sun}_), our new measurements more than double the number of ~2.5Gyr benchmark rotators and extend this sample down to ~0.55M_{sun}_. The slowly rotating sequence for this joint sample appears relatively flat (22{+/-}2days) compared to sequences for younger clusters. This sequence also intersects the Kepler intermediate-period gap, demonstrating that this gap was not created by a lull in star formation.