Completing the Massive Star Population: Striking Into the Field

TL;DR

This review explores the origins, properties, and significance of field massive stars, highlighting their dual formation pathways and implications for star formation and stellar evolution theories.

Contribution

It provides a comprehensive analysis of the origins and characteristics of field massive stars, integrating observational data and surveys like RIOTS4.

Findings

Field massive stars originate both in situ and as runaways.

The properties of field and cluster massive stars are compared across the Magellanic Clouds and Galaxy.

Field massive stars constitute 20-25% of the high-mass stellar population.

Abstract

As a population, field massive stars are relatively enigmatic, and this review attempts to illuminate this sector of the high-mass stellar population, which comprises 20 - 25% of the massive stars in star-forming galaxies. The statistical properties of the field population are vital diagnostics of star formation theory, cluster dynamical evolution, and stellar evolution. We present evidence that field massive stars originate both in situ and as runaways from clusters, based on the clustering law, IMF, rotation velocities, and individual observed in situ candidate field stars. We compare the known properties of field and cluster massive stars from studies in the Magellanic Clouds and the Galaxy, including our RIOTS4 complete spectroscopic survey of SMC OB stars. In addition to the origin of the field massive stars, we discuss additional properties including binarity, runaway mechanisms, and some evolved spectral types.