Refining the Census of the Upper Scorpius Association with Gaia

TL;DR

This study refines the star and brown dwarf census of the Upper Scorpius association using Gaia data, spectroscopic verification, and disk analysis, providing updated membership, age, and disk fraction estimates.

Contribution

It updates the membership list of Upper Sco with Gaia astrometry, spectroscopic data, and disk analysis, and compares its age to other young associations.

Findings

Catalog of 1761 confirmed members.

Disk fraction increases with lower stellar mass.

Upper Sco is approximately half as old as beta Pic.

Abstract

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.