The origin of blue straggler stars in star clusters

• Applicant: Professor Dr. Pavel Kroupa
• Subject Area: Astrophysics and Astronomy
• Term: from 2011 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 196496450

• Final Report Year: 2018

Final Report Abstract

With this project it has been shown for the first time that a fully-realistic young stellar population which is consistent with independent observational constraints (physical models of YMCs, very high birth binarity, canonical upper mass limit near 150 M⊙) naturally produces “monster stars” in massive star-burst clusters such as R136, as well as comparable field stars which are however ejected from such a cluster. It has also been shown for the first time that the IMF in R136 must have been slightly top-heavy, because the ejected massive stars need to be accounted for statistically. Calculations of globular clusters with primordial binaries have shed light on the possible emergence of a double blue straggler sequence, and its association with core collapse. With this project, Nbody models of star clusters have been pushed to new limits, and the unique Aarseth codes have been found to perform exceedingly well. The results have been published in a number of peer-reviewed research papers.

Publications

• 2012, A&A, 547, A23–A27, “On the true shape of the upper end of the stellar initial mass function. The case of R136”
  Banerjee, S., & Kroupa, P.
  
• 2012, ApJ, 746, 15–23, “Runaway Massive Stars from R136: VFTS 682 is Very Likely a Slow Runaway”
  Banerjee, S., Kroupa, P., & Oh, S.
  
• 2012, MNRAS, 426, 1416–1426, “The emergence of super-canonical stars in R136-type starburst clusters”
  Banerjee, S., Kroupa, P., & Oh, S.
  
• 2014, MNRAS, 437, 4000–4005, “R144: a very massive binary likely ejected from R136 through a binary-binary encounter”
  Oh, S., Kroupa, P., & Banerjee, S.