The decay of OB-star cores of ONC-type star clusters

• Applicant: Professor Dr. Pavel Kroupa
• Subject Area: Astrophysics and Astronomy
• Term: from 2007 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 44929370

The distribution of massive stars, clustered or in the field, imposes constraints on their formation and on the evolution of galaxies. Inspecting the status of the nearest massive-star forming site, the Trapezium in the Orion Nebula cluster (ONC) and the OB population of the ONC, two discrepancies arise: i) The Trapezium at the centre of the ONC, which today contains 4 OB star-systems, is expected to have totally dynamically decayed by now — it should not exist anymore ii) Given the total mass of the ONC. about 40 OB stars are expected to have formed in it but only ten are observed. These problems have been studied using an OB-star core model consisting of 40 OB stars having an initial spatial extent like the Trapezium (Pflamm-Altenburg & Kroupa, 2006). Although this model is based on some simplifications (no surrounding cluster potential, no relaxation with low-mass stars, no primordial binaries and no physical collisions) it confirms that only 25 % of all formed OB stars remain in the ONC after 1 Myr. The majority are shot-out from the ONC core through strong dynamical encounters.Primordial binaries axe, however, expected to increase the OB-star deficit even more once they are included in the modelling. It is the aim of this project to improve and to extend the existing OB-core model of the ONC by including primordial binaries, two-body relaxation between OB-core stars and low-mass cluster stars, the gravitational potential created by the remaining stars and physical collisions, and to compare the obtained numerical data on the wide-scale OB-star distribution with data from OB-star catalogues.

• DFG Programme: Research Grants