Stellar cluster

R.D. Jeffries Lithium depletion in open clusters . In Stellar Clusters and Associations Convection, Rotation, and Dynamos, ASP Proceedings Vol. 198, ed. by R. Pallavicini, G. Micela, and S. Sciortino (ASP, San Francisco 2000) p.245... 

Multiple lines of evidence exist for a population of live radionuclides, such as 26Al or 60Fe, which were injected into the proto-solar cloud or disk prior to the formation of CAIs (e.g. Tachibana et al. 2006). Isotopic abundances suggest that the isotopes have originated in a supernova, possibly with a very massive star progenitor that also underwent a Wolf-Rayet phase (Bizzarro et al. 2007). If this interpretation is correct, the Sun must have formed in a very rich and dense stellar cluster, such as the Carina Nebula, very much unlike the Taurus or other low-mass star-forming regions. Luminous massive stars in such clusters may truncate or fully evaporate protoplanetary disks around other cluster members. Two key questions remain open. How close in time and space did the supernova explode... 

The density and temperature distribution of interstellar matter, contrary to its elemental composition, is strongly inhomogeneous. At least three different phases exist (e.g. Tielens 2005) (i) extended low-density bubbles of hot ionized gas (hot interstellar medium or HIM, mass fraction 0.003, volume fraction 0.5), resulting from series of SN explosions in mass-rich stellar clusters (ii) cold and dense clouds of neutral gas (cold and neutral interstellar medium or CNM, mass fraction 0.3, volume fraction 0.01), resulting from sweeping up of warm gas and (iii) a warm, either ionized or neutral, medium in between (warm interstellar medium or WIM, mass fraction 0.5, volume fraction 0.5). The essential properties of the three phases are indicated in Fig. 2.4. The coolest and most massive of the clouds are the molecular clouds (MC, mass fraction 0.2, volume fraction 0.0005), a separate component, that are the places of star formation, where new stars are formed as stellar clusters with total masses between about 200 and several 106 M0. 

Massive stars return mass into the HIM, because almost all massive stars in rich stellar clusters end their life within the super-bubble driven into the ISM by the SN explosions (e.g. Higdon Lingenfelter 2005). The expansion of the bubble is also largely responsible for the dispersion of the remaining part of the MC within which the cluster has formed. Due to their long lifetimes the mass return by low-and intermediate-mass stars occurs well after the dissolution of their parent stellar clusters. By that time they have become randomly distributed field stars. Because of the large volume-filling factors of HIM and WIM the mass return of these stars is to HIM and WIM, but not to CNM. 

Planetary systems are now generally believed to be by-products of the process of star formation. Star formation, therefore, is the natural starting point for discussions of planet formation. Almost all stars are born as members of stellar clusters that, in turn, are bom in molecular clouds. Formation of isolated stars seems to be possible according to observations, but this is a rare process. Whether the Sun and its associated planetary system formed in isolation or as member of a cluster is not known some indications hint to formation in a cluster (see Hester Desch 2005 Gounelle Meibom 2008 and Chapter 9, this volume). 

Summary of Spitzer Observations of Young Stellar Clusters... 

Key wordsi Star Formation - Stellar Clusters - Compact HU Regions... 

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