New Parallaxes for the Upper Scorpius OB Association

TL;DR

This study provides new parallax measurements for 52 stars in Upper Scorpius, revealing age differences related to circumstellar disks and exploring the group's formation history with kinematic data.

Contribution

It offers the first set of parallaxes for low-mass stars in Upper Scorpius and analyzes their ages and kinematics to understand star formation and evolution.

Findings

Stars without disks are younger (~4.9 Myr) than those with disks (~8.2 Myr).

Kinematic traceback is limited by measurement uncertainties, affecting age estimates.

Age differences suggest evolutionary effects influence apparent stellar ages.

Abstract

Upper Scorpius is a subgroup of the nearest OB association, Scorpius--Centaurus. Its young age makes it an important association to study star and planet formation. We present parallaxes to 52 low mass stars in Upper Scorpius, 28 of which have full kinematics. We measure ages of the individual stars by combining our measured parallaxes with pre-main sequence evolutionary tracks. We find there is a significant difference in the ages of stars with and without circumstellar disks. The stars without disks have a mean age of 4.9+/-0.8 Myr and those with disks have an older mean age of 8.2+/-0.9 Myr. This somewhat counterintuitive result suggests that evolutionary effects in young stars can dominate their apparent ages. We also attempt to use the 28 stars with full kinematics (i.e.\ proper motion, radial velocity, and parallax) to trace the stars back in time to their original birthplace to obtain a trackback age. We find, as expected given large measurement uncertainties on available radial velocity measurements, that measurement uncertainties alone cause the group to diverge after a few Myr.