A Pan-STARRS + UKIDSS Search for Young, Wide Planetary-Mass Companions in Upper Scorpius

TL;DR

This study used combined optical and NIR data from Pan-STARRS 1 and UKIDSS to discover and analyze wide, young planetary-mass companions in Upper Scorpius, revealing their properties and frequency.

Contribution

It presents a deeper search method for wide substellar companions and reports new discoveries with detailed spectral and luminosity analysis.

Findings

Identified several new wide substellar companions in Upper Scorpius.

Found companions with masses around 15-60 Mjup and large separations up to 3200 AU.

Discovered companions are more luminous than expected, suggesting different formation or accretion histories.

Abstract

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 Mjup. Our search is ~4mag deeper than previous work based on 2MASS. We identified several candidates around known stellar members using a combination of color selection and spectral energy distribution fitting. Our followup 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 Mjup, indicating a frequency for such wide substellar companions of ~0.6+/-0.3%. Both USco1610-1913B and USco1612-1800B are more luminous than expected for their spectral type compared with known members of Upper Sco. HIP77900B has an extreme mass ratio (M2/M1~0.005) and an extreme separation of 3200 AU. USco1602-2401B also has a very large separation of 1000 AU. We have also confirmed a low-mass stellar companion, USco1610-2502B (730AU, 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.