OB Stars in Stochastic Regimes

TL;DR

This paper investigates the statistical properties of OB stars in sparse clusters, providing evidence that the maximum stellar mass is largely independent of the cluster mass, which informs the understanding of the stellar initial mass function.

Contribution

It offers new statistical analysis of OB stars in sparse clusters, supporting the idea that the upper stellar mass limit is constant across different cluster masses.

Findings

Observed OB star counts are consistent with a constant upper-mass limit.

Sparse OB clusters align with Monte Carlo simulations of cluster populations.

Maximum stellar mass appears largely independent of cluster mass.

Abstract

The highest-mass stars have the lowest frequency in the stellar IMF, and they are also the most easily observed stars. Thus, the counting statistics for OB stars provide important tests for the fundamental nature and quantitative parameters of the IMF. We first examine some local statistics for the stellar upper-mass limit itself. Then, we examine the parameter space and statistics for extremely sparse clusters that contain OB stars, in the SMC. We find that thus far, these locally observed counting statistics are consistent with a constant stellar upper-mass limit. The sparse OB star clusters easily fall within the parameter space of Monte Carlo simulations of cluster populations. If the observed objects are representative of their cluster birth masses, their existence implies that the maximum stellar mass is largely independent of the parent cluster mass.