Proper motions of Upper Sco T-type candidates

TL;DR

This study reevaluates five T-type candidate objects in Upper Scorpius using new photometry and proper motion data, challenging previous membership assumptions and suggesting a possible turnover in the mass function at very low masses.

Contribution

It provides updated measurements that question prior classifications and offers insights into the low-mass end of the Upper Sco mass function.

Findings

New data do not support previous membership claims.

Potential turnover in the mass function below 10^-4 Jupiter masses.

Implications depend on age and models used for Upper Sco.

Abstract

We present new z- and H-band photometry and proper motion measurements for the five candidate very-low-mass T-type objects we recently proposed to be members of the nearest OB association to the Sun, Upper Scorpius. These new data fail to corroborate our prior conclusions regarding their spectral types and affiliation with the Upper Scorpius population. We conclude that we may be in presence of a turnover in the mass function of Upper Sco taking place below 10-4 Jupiter masses, depending on the age assigned to Upper Sco and the models used.