Outflows of Massive Stars in Cluster

Massive stars often tend to be in cluster when they form in molecular clouds, and bipolar molecular outflows occur during the forming process of stars. On the basis of newly observed bipolar molecular outflows associated with massive stars, three properties are proposed to statistically identify massive stars whether in cluster or not as the driving engines of the flows. For clustering massive stars with some exceptions, their outflow collimation factors are generally poor and less than two, and the correlations of the flow momentum rate and the mass flow rate with the central source bolometric luminosity deviate the ones for selected well-resolved 16 flows.