Are binary-star populations regionally different? --in memory of Sverre Aarseth--

TL;DR

This paper discusses modeling stellar populations in clusters and galaxies, emphasizing the importance of initial binary properties, their dynamical evolution, and how these influence observable differences across regions.

Contribution

It introduces a comprehensive approach using Nbody simulations to infer initial conditions of star clusters and predict stellar merger rates and observable properties.

Findings

Initial binary properties vary with star formation conditions

Dynamical processing explains observed population differences

Predictions include merger rates and extragalactic observables

Abstract

For synthesising star clusters and whole galaxies, stellar populations need to be modelled by a set of four functions that define their initial distribution of stellar masses and of the orbital properties of their binary-star populations. The initial binaries are dynamically processed in different embedded clusters explaining differences in the observed populations. The approach summarised here, for which the Aarseth Nbody codes have been instrumental, allows inference of the initial conditions of the globular cluster omega Cen and the quantification of the stellar merger rate as a function of stellar spectral type, of the role of multiples and mergers for the Cepheid population, and predictions of extragalactic observables. The observability of the four initial distribution functions and their physical and philosophical meaning are also briefly raised. Evidence for the variation of these functions on the physical conditions of star formation and future steps towards extensions to include higher-order multiple systems are touched upon.