On a Formation Scenario of Star Clusters |
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Authors: | Christian Theis |
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Institution: | 1. Institut f. Theoretische Physik und Astrophysik, Universit?t Kiel, 24098, Kiel, Germany
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Abstract: | Most formation scenarios of globular clusters assume a molecular cloud as the progenitor of the stellar system. However, it
is still unclear, how this cloud is transformed into a star cluster, i.e. how the destructive processes related to gas removal
or low star formation effiency can be avoided. Here a scheme of supernova (SN) induced cluster formation is studied. According
to this scenario an expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in
star formation in the shell. Provided the stellar shell expands sufficiently slow, its self-gravity stops the expansion and
the shell recollapses, by this forming a stellar system. I present N-body simulations of collapsing shells which move in a
galactic potential on circular and elliptic orbits. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters over a large range of galactocentric distances. Outside this range single stellar systems
are formed, whereas at small galactocentric distances the shells are tidally disrupted. In that case many small fragments
formed during the collapse survive as single bound entities. About 1/3 of the twin cluster systems formed on circular orbits
merge within 400 Myr. On elliptic orbits the merger rate reduces to less than 4%. Thus, there could be a significant number
of twin clusters even in our Galaxy, which, however, might be undetected as twins due to a large phase shift on their common
orbit.
This revised version was published online in September 2006 with corrections to the Cover Date. |
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Keywords: | globular cluster stellar dynamics |
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