Refining the Census of the Upper Scorpius Association with Gaia
  We have refined the census of stars and brown dwarfs in the Upper Sco
association (~10 Myr, ~145 pc) by 1) updating the selection of candidate
members from our previous survey to include the high-precision astrometry from
the second data release of Gaia, 2) obtaining spectra of a few hundred
candidate members to measure their spectral types and verify their youth, and
3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward
Upper Sco that show evidence of youth in this work and previous studies. We
arrive at a catalog of 1761 objects that are adopted as members of Upper Sco.
The distribution of spectral types among the adopted members is similar to
those in other nearby star-forming regions, indicating a similar initial mass
function. In previous studies, we have compiled mid-infrared photometry from
WISE and the Spitzer Space Telescope for members of Upper Sco and used those
data to identify the stars that show evidence of circumstellar disks; we
present the same analysis for our new catalog of members. As in earlier work,
we find that the fraction of members with disks increases with lower stellar
masses, ranging from <=10% for >1 Msun to ~22% for 0.01-0.3 Msun. Finally, we
have estimated the relative ages of Upper Sco and other young associations
using their sequences of low-mass stars in M(G_RP) versus G_BP-G_RP. This
comparison indicates that Upper Sco is a factor of two younger than the beta
Pic association (21-24 Myr) according to both non-magnetic and magnetic
evolutionary models.
