APOGEE strings: a fossil record of the gas kinematic structure

TL;DR

This study reveals that young stars in Orion A form elongated strings with similar velocities, indicating they retain the gas substructure from their birth environment, bridging stellar and gas kinematics.

Contribution

It introduces the identification of stellar strings with low velocity dispersion, linking stellar kinematic substructure to the parental gas structures in Orion A.

Findings

37 stellar groups identified with similar RVs

Stars form elongated chains of 1-1.5 pc length

Stellar kinematics mirror gas substructure

Abstract

We compare APOGEE radial velocities (RVs) of young stars in the Orion A cloud with CO line gas emission and find a correlation between the two at large-scales, in agreement with previous studies. However, at smaller scales we find evidence for the presence of substructure in the stellar velocity field. Using a Friends-of-Friends approach we identify 37 stellar groups with almost identical RVs. These groups are not randomly distributed but form elongated chains or strings of stars with five or more members with low velocity dispersion, across lengths of 1-1.5~pc. The similarity between the kinematic properties of the APOGEE strings and the internal velocity field of the chains of dense cores and fibers recently identified in the dense ISM is striking and suggests that for most of the Orion A cloud, young stars keep memory of the parental gas substructure where they originated.