On the Efficiency of Field Star Capture by Star Clusters

An exciting recent finding regarding scaling relations among globular clusters is the so-called `blue tilt': clusters of the blue sub-population follow a trend of redder colour with increasing luminosity. In this contribution we estimate by means of collisional N-body simulations to which extent this trend can be explained by field star capture occurring over a Hubble time. We investigate star clusters with 10³ to 10⁶ stars. We find that the ratio between captured field stars and total number of clusters stars is very low (≲ 10⁻⁴), even for co-rotation of the star cluster in a cold disk. This holds for star clusters in the mass range of both open clusters and globular clusters. Therefore, field star capture is not a probable mechanism for creating the colour-magnitude trend of metal-poor globular clusters.