Low Mass Stars as Tracers of Star and Cluster Formation

Abstract We review the use of young low mass stars and protostars, or stellar objects (YSOs), as tracers star formation. Observations molecular clouds at visible, infrared, radio X-ray wavelengths can identify characterize YSOs populating these clouds, with ability to detect deeply embedded all evolutionary stages. Surveys Spitzer, Herschel, XMM-Newton Chandra space telescopes have measured spatial distribution within a number nearby (<2.5 kpc) showing surface densities varying by more than three orders magnitude. These surveys been used measure spatially formation rates efficiencies when combined maps gas, led discovery star-forming relations clouds. YSO also structures, ages, histories clusters, they illuminate relationship clusters networks filaments, hubs ridges in from which form. Measurements proper motions radial velocities trace evolving kinematics phases through gas dispersal, providing insights into factors that shape bound clusters. On 100 pc scales encompass entire complexes, Gaia is mapping associations dispersed their natal exist alongside reveal complex structures associations, show evidence for supernova driven expansions. Remnants now identified Gaia, traces persist few hundred million years.