Taurus and Upper Sco brown dwarfs phot. and masses

This corresponds to an overall binary fraction of 1.8^+2.6^_-1.3_% among low-mass brown dwarfs and free-floating planetary mass objects over the separation range >7au. Despite the limitations of small-number statistics and variations in spatial resolution and sensitivity, our results, combined with previous high-spatial-resolution surveys, suggest a notable difference in the multiplicity properties of objects below ~30-50Mjup between Upper Sco and Taurus.

In Taurus, a binary fraction of 5.6^+3.2^_-2.3_% is found for objects with masses below 30Mjup, and of 7.8^+3.0^_-2.4_% for objects with masses below 50Mjup, whereas no binary were found among 80 objects over the matching luminosity range in Upper Sco, corresponding to an upper limit of >=1.2%. This difference may point to intrinsically distinct formation conditions, with warmer parental molecular clouds originally present in Upper Sco potentially inhibiting fragmentation into the lowest-mass brown dwarfs and free-floating planets compared to cooler environments such as Taurus.