N-BODY SIMULATIONS

work of Nela Dvořáková, Daniela Korčáková , Pavel Kroupa & František Dinnbier

• dynamical evolution of the birth cluster leads to the creation of mergers
  ⇒ there is no need of the triple or multiple systems to create a merger

  The interaction of stars in the birth cluster may lead to the ejection of the binary from the cluster. Such binaries have large eccentricity and short semi-major axis. In such situation, the tidal forces circularize the orbit and as a consequence of the momentum conservation, the semi-major axis shrink.

• about 1.7% of stars are involved in mergers
• about 50% of mergers are B-type stars, that is equal to 12.5% of all B-type stars ⇒ it is pretty high chance to find more post-mergers among FS CMa stars
  Such large percentage of mergers in B-type group is a natural consequence of the initial mass function, initial distribution of the binary star parameters and the large range of masses of B-type stars.
  There are two distributions in the figure. The blue one are test calculations when the threshold between different binary star parameters is 2 M_⊙. This threshold is necessary to include, because low- and high- mass stars are formed differently.

  

• most merger events occur during the common envelope phase

  

• distribution of mergers according the individual spectral types

  

• comparison with the observations:

  

  We use the W component of the space velocity. Note, the distributions must be re-scaled, because there is only a few observed FS CMa stars with good quality spectra. We must remove the central part, the regions along the galactic plane, because of large extinction and therefore a lack of detected stars.

• some merger events occur out of the Milky Way ⇒ enrichment of the intergalactic matter