Kinematics of Stars Ejected from Young Clusters in N-body

SimulationsChristina Schoettler

Supervisor: Dr Richard Parker The University of Sheffield, UK

cschoettler1@sheffield.ac.uk

1. The initial conditions

1. Initial substructureHighly substructured Smooth, sphere-like

1. Initial substructureHighly substructured Smooth, sphere-like

1. Initial virial ratio

• Subvirial (‘cool’)αvir = 0.1

• Virial (‘tepid’)αvir = 0.5

1. The initial conditions - summarised• 2 levels of initial substructures (fractal method: Goodwin & Whitworth 2004)

• 2 initial virial ratios• 20 simulations each with 1000 stars per cluster • Maschberger IMF (Maschberger 2013)

• Initial radius = 1 pc• 10 Myr evolution• No primordial binaries, gas or stellar evolution

• Starlab N-body integrator kira (Portegies Zwart et al. 2001)

(for dynamical evolution, see also Parker et al. 2014, Parker & Wright 2016)

2. Ejected/unbound fraction

2. Initially subvirial clustersHighly substructured Smooth, sphere-like

2. Initially subvirial clustersHighly substructured Smooth, sphere-like

2. Initially virialised clustersHighly substructured Smooth, sphere-like

3. Proper motion of ejected\unbound stars at 5 Myr

3. Proper motion of ejected/unbound starsHighly substructured Smooth, sphere-like

3. Proper motion of ejected/unbound starsSmooth, sphere-likeHighly substructured

3. Proper motion of ejected/unbound starsSmooth, sphere-likeHighly substructured

3. Runaway stars (> 30 km/s)?

3. Walkaway stars (>10 km/s)?

Conclusions• Changing initial virial ratio and substructure has an effect on ejection/unbound

fractions resulting low-mass and high-mass star fractions are not the same

• Median velocities (proper motion) of ejected/unbound stars are higher in initially substructured clusters and highest when clusters are also initially subvirial (Allison 2012) these clusters also produce the fastest stars

• Ejected/unbound low-mass stars have lower median velocities compared to high-mass stars all-throughout the simulation

• All 4 ‘runaway’ stars (>30 km/s) are low-mass; 2 high-mass ‘walkaways’ at >10 km/s, accompanied by a large number of low-mass ‘walkaways’