A Pan-Starrs + Ukidss Search for Young, Wide Planetary-Mass Companions in Upper Scorpius

We have combined optical and NIR photometry from Pan-STARRS 1 and UKIDSS to search the young (5–10 Myr) star-forming region of Upper Scorpius for wide (≈400–4000 AU) substellar companions down to ∼5 M Jup . Our search is ≈4 mag deeper than previous work based on the Two Micron All Sky Survey. We identified several candidates around known stellar members using a combination of color selection and spectral energy distribution fitting. Our follow-up spectroscopy has identified two new companions as well as confirmed two companions previously identified from photometry, with spectral types of M7.5–M9 and masses of ∼15–60 M Jup , indicating a frequency for such wide substellar companions of ∼0.6% ± 0.3%. Both USco 1610−1913B and USco 1612−1800B are more luminous than expected for their spectral type compared with known members of Upper Sco. HIP 77900B has an extreme mass ratio ( M 2 / M 1 ≈ 0.005) and an extreme separation of 3200 AU. USco 1602−2401B also has a very large separation of 1000 AU. We have also confirmed a low-mass stellar companion, USco 1610−2502B (730 AU, M5.5). Our substellar companions appear both non-coeval with their primary stars according to evolutionary models and, as a group, are systematically more luminous than the Upper Sco cluster sequence. One possible reason for these luminosity discrepancies could be different formation processes or accretion histories for these objects.