AAS Meeting #193 - Austin, Texas, January 1999
Session 105. Galaxy Kinematics and Dynamics
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[105.08] Can Round Star Clusters Form From Flattened Clouds?

S.D. Murray (LLNL), D.A. Raymondson (UC Davis), R.A. Urbanski (Las Positas College)

We report upon the results of N-body simulations of star formation resulting from mergers during the collapse of dynamically cold, flattened systems of cloudlets. Such evolution is expected to occur in several models of cluster star formation. As was found previously in the case of spherical systems, the resulting star clusters have half-mass radii which are significantly smaller than the initial values of the systems. Stars which form early in the collapse have large final radii, and retain a strong memory of the initial ellipticity of the system. Stars which form later have smaller final radii, and retain less memory. If we examine only those stars within the final half-mass radii of the models, we find that they follow a much less ellipsoidal distribution than do stars at larger radii. Their ellipticities, however, generally exceed those of young, dynamically unevolved massive star clusters in the LMC. The best comparisons with the observed ellipticities are found in models for which the initial minor-to-major axis ratios exceed \approx.2, kinetic-to-potential energy ratios exceed \approx0.1, covering factors, f\tau are below \approx0.2, or initial cloud masses Mi\ll MG, where MG is the critical mass for gravitational instability. All of these ranges of parameters tend to delay the onset of star formation until late in the collapse, when the system is less elliptical. Systems with Mi\ll MG tend to produce very flat stellar IMF's, much flatter than observed. Unless, therefore, f\tau\approx0.2 or below results from the fragmentation of the parent cloud, systems such as the young LMC clusters are unlikely to have formed from extremely flattened or dynamically cold initial conditions, even in the presence of dissipation during star formation.

The author(s) of this abstract have provided an email address for comments about the abstract: sdmurray@llnl.gov

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