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MODEST Working Group 1: 

Star Formation

 Model of Turbulent Molecular Cloud Fragmentation

 

In order to follow the evolution of a dense stellar system, one has to know (or choose) the initial conditions of that system. Traditionally, the starting points have been Plummer or King models, i.e. systems which include only zero-age main sequence stars evenly distributed throughout the cluster, and no gas, star formation, or  proto-stellar disks. However, we know that most of these assumptions are at best simple and at worst downright wrong.

Modern star formation theory considers supersonic interstellar turbulence, ubiquitously observed in star forming molecular clouds, as controlling agent for stellar birth. In this picture, essentially all properties of nascent star clusters depend on the interplay between gravity the turbulent velocity field. Inefficient, isolated star formation will occur in regions which are supported by turbulence carrying most of its energy on very small scales.  Clusters of stars build up in molecular cloud regions where self-gravity overwhelms turbulence, either because such regions are compressed by a large-scale shock, or because interstellar turbulence is not replenished and decays on short timescales. Rich star clusters, thus, are expected to form highly-substructured and with dynamical interactions between protostars becoming common. This modifies the mass accretion rates, leads to mass segregation, and influences the resulting IMF, all with important consequences for the subsequent evolution of the cluster.

A full understanding of star cluster evolution needs to take the formation processes into account. A complete and comprehensive numerical description of star cluster evolution, therefore, requires the combination with (or at least input from) realistic gasdynamical models of molecular cloud fragmentation and star cluster build-up.
 

 WG1 can contribute to the following list of topics:
 
Transition from Hydrodynamics to Stellardynamics - embedded evolution 
  (accretion, gas dominated stellardynamics)
- gas removal (timescale)
- feedback processes (winds, outflows, UV radiation, etc.)
Substructure of young clusters - are embedded clusters substructured?
- to what degree?
- how quickly is substructure erased?
Primordial binaries - fraction of primordial binaries 
  (mass ratios, eccentricities, semimajor axes)
- and higher-order systems (transition to substructure)
PMS tracks - stellar radii (needed for collisions)
- evolutionary track (for feedback timing)

 
 
Groups working on these problems
(incomplete list, theorists only) 		 - M. Bate (Exeter, UK)
- I. Bonnell (St. Andrews, UK)
- A. Burkert (Munich, D)
- C. Clarke (Cambridge, UK)		 - R. Klessen (Potsdam, D)
- P. Kroupa (Kiel, D)
- R. Spurzem (Heidelberg, D)
- A. Whitworth (Cardiff, UK) 

 
WG1 contact: Ralf Klessen  (rklessen@aip.de)   Pavel Kroupa (pavel@astrophysik.uni-kiel.de)