Using rapid rotators as tracers of multiplicity statistics as a function of stellar density

TL;DR

This study investigates how the fraction of rapid rotators, often binaries, varies with stellar density in young and older stellar populations, revealing insights into binary formation and evolution.

Contribution

It introduces a novel analysis of rapid rotators as tracers of binary statistics across different stellar densities and ages, highlighting environmental effects on binary survival.

Findings

Deficit of rapid rotators in dense clusters like Orion Nebula.

Higher density regions in older populations have more rapid rotators.

Stellar interactions influence binary formation and dissolution.

Abstract

Recent works have identified that rapidly rotating stars are predominantly binaries with separations of a few to a few tenths of au. This is a crucial range of separation that is often inaccessible to searches of binary stars, providing a unique opportunity to examine their statistical properties. In particular, we have performed an analysis of rapid rotators in young moving groups. We examined their fraction as a function of the stellar density of the population in which they are found. We find that there is a deficit of rapid rotators in dense clusters such as the Orion Nebula in comparison to the more diffuse parts of the Orion Complex, as intracluster interactions with neighboring stars likely dissolve binaries with intermediate separations before they had a chance to fully form. In contrast, in older populations with an age of $\sim100$ Myr, mass segregation redistributes binaries relative to single stars, thus in such older regions, rapid rotators are predominantly found in the regions of higher stellar density. This work sheds light on both the conditions that lead to the formation of binary stars and their dynamical evolution.