Measuring Turbulence with Young Stars in the Orion Complex
  Stars form in molecular clouds in the interstellar medium (ISM) with a
turbulent kinematic state. Newborn stars therefore should retain the turbulent
kinematics of their natal clouds. Gaia DR2 and APOGEE-2 surveys in combination
provide three-dimensional (3D) positions and 3D velocities of young stars in
the Orion Molecular Cloud Complex. Using the full 6D measurements, we compute
the velocity structure functions (VSFs) of the stars in six different groups
within the Orion Complex. We find that the motions of stars in all diffuse
groups exhibit strong characteristics of turbulence. Their first-order VSFs
have a power-law exponent ranging from $\sim0.2-0.5$ on scales of a few to a
few tens of pc, generally consistent with Larson's relation. On the other hand,
dense star clusters, such as the Orion Nebula Cluster (ONC), have experienced
rapid dynamical relaxation, and have lost the memory of the initial turbulent
kinematics. The VSFs of several individual groups and the whole Complex all
show features supporting local energy injection from supernovae. The measured
strength of turbulence depends on the location relative to the supernova
epicenters and the formation history of the groups. Our detection of turbulence
traced by young stars introduces a new method of probing the turbulent
kinematics of the ISM. Unlike previous gas-based studies with only projected
measurements accessible to observations, we utilize the full 6D information of
stars, presenting a more complete picture of the 3D interstellar turbulence.
