Hydrogen Line Study of Stellar Associations and Clusters

This paper describes the results of recent investigations at Harvard College Observatory on the interstellar structure around a number of stellar associations and clusters. The results were obtained from analyses of the 21-cm profiles of neutral hydrogen in these systems using the 24-foot and 60-foot radio telescopes at the Agassiz Station of Harvard College Observatory. Investigations of the associations Orion I and Orion II showed expansion of neutral hydrogen around these associations. Preliminary results of studies of other associations Lacerta, Cygnus II, Cygnus VI, NGC 2244, and NGC 2264 are described. Observations of hydrogen content of some galactic clusters were found to show a strong age effect. The significance of the above results for studies of stellar evolution is discussed.