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2000ApJ...540..255P - Astrophys. J., 540, 255-270 (2000/September-1)
Accelerating star formation in clusters and associations.
PALLA F. and STAHLER S.W.
Abstract (from CDS):
Our investigation corroborates and extends our previous results on the Orion Nebula Cluster. In all cases, we find that star formation began at a relatively low level some 107 yr in the past and has more recently undergone a steep acceleration. This acceleration, which lasts several million years, is usually continuing through the present epoch. The one clear exception is the OB association Upper Scorpius, where the formation rate climbed upward, peaked, and has now died off. Significantly, this is also the only region of our list that has been largely stripped of molecular gas.
The acceleration represents a true physical phenomenon that cannot be explained away by incompleteness of the samples; nor is the pattern of stellar births significantly affected by observational errors or the presence of unresolved binaries. We speculate that increasing star formation activity arises from contraction of the parent cloud. Despite the short timescale for acceleration, the cloud is likely to evolve quasi-statically. Star formation itself appears to be a critical phenomenon, occurring only in locations exceeding some threshold density. The cloud's contraction must reverse itself, and the remnant gas dissipate, in less than 107 yr, even for aggregates containing no massive stars. In this case, molecular outflows from the stars themselves presumably accomplish the task, but the actual dispersal mechanism is still unclear.
Abstract Copyright: ∼
Journal keyword(s): open clusters and associations: individual (Chamaeleon, IC 348, Lupus, NGC 2264, Orion Nebula Cluster, ρ Ophiuchi, Taurus-Auriga, Upper Scorpius) - Stars: Evolution - Stars: Formation - Stars: Pre-Main-Sequence
CDS comments: p. 264, 265 : W178 = NGC 2264 178
Simbad objects: 44
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