A Pan-STARRS1 Proper-Motion Survey for Young Brown Dwarfs in the Taurus and the Upper Scorpius Star-Forming Regions

Young brown dwarfs are of prime importance to investigate the universality of the initial mass function (IMF) and to understand the physical connections between substellar and planetary-mass objects. Pan-STARRS1 (PS1) 3π survey (δ ≥ -30^○) is finished and has obtained stacked images reaching down to the planetary regime (≤ 13 M_Jup) in nearby star-forming regions, thus providing an innovative tool to search for brown dwarfs. Using photometry and astrometry from PS1, WISE, 2MASS and UKIDSS, we are performing the widest and deepest brown dwarf survey in Taurus (≈370 deg², ∼1 Myr) and Upper Scorpius (USco, ≈450 deg², ∼10 Myr), which are among the closest star-forming regions. Our work is the first to measure proper motions, a robust proxy of membership, for Taurus and USco brown dwarf candidates over such large area and long time baseline (∼13 yr by combining PS1 and 2MASS). Our spectroscopic follow-up has found the lowest-mass objects in both regions (Taurus: ≈ 6 M_Jup USco: ≈ 14 M_Jup), and has yielded a success rates of ≈ 80% and ≈ 90% in Taurus and USco, respectively, far better than any previous searches (≤ 50%). Our newly confirmed members have already added ≈ 60% more brown dwarfs in USco and more than doubled the number of L-type members (≤ 20 M_Jup) in both regions. Upon completion, our discoveries will be a significant addition to the substellar regimes of the Taurus and the USco IMF and will provide more benchmarks to investigate the compositions of substellar and planetary atmospheres.