Recent analyses of the Gaia data have identified diffuse stellar populations surrounding nearby open clusters. It is important to verify that these "halos," "tails," and "strings" are of similar ages and compositions as stars in the denser part of the cluster. We present an analysis of NGC2516 (~150Myr), which has a classical tidal radius of 10pc and an apparent halo of stars spanning 500pc (20{deg} on-sky). Combining photometry from Gaia, rotation periods from TESS, and lithium measurements from Gaia-ESO and GALAH, we find that the halo of NGC2516 is the same age as the cluster's core. Two-thirds of kinematically selected halo members out to 250pc from the cluster center have rotation periods consistent with a gyrochronological age of 150Myr. A comparison sample of field stars shows no such trend. The lithium abundances of stars in the halo are higher than in the field and correlated with the stellar rotation rate and binarity fraction, as has been noted in other young open clusters. Broadly speaking, this work supports a new paradigm wherein the halos of open clusters are often more populous than their cores. We highlight implications for spectroscopic survey targeting, open cluster dispersal, and planet searches around young stars.

Cone search capability for table J/AJ/162/197/table1 (Rotation periods and lithium equivalent widths for 3298 candidate NGC2516 members)