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

Priyanka Cingirikonda, Marina Kounkel, Joseph Mullen

TL;DR

This study uses rapid rotators as proxies for binaries with intermediate separations to investigate how environment affects multiplicity. By combining TESS rotational periods, gyrochronology, and Gaia-based 3D density measurements across six young moving groups, the authors quantify how the rapid-rotator fraction varies with local density and age. They find a deficit of rapid rotators in dense regions for the youngest groups, suggesting fewer such binaries or early disruption in crowded environments, while older groups show a reversal consistent with mass segregation driving binaries toward denser cluster centers. The results imply environment- and age-dependent formation and dynamical processing of intermediate-separation binaries, though they remain preliminary and require follow-up confirmation of the binary nature of the rapid rotators.

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.

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

TL;DR

This study uses rapid rotators as proxies for binaries with intermediate separations to investigate how environment affects multiplicity. By combining TESS rotational periods, gyrochronology, and Gaia-based 3D density measurements across six young moving groups, the authors quantify how the rapid-rotator fraction varies with local density and age. They find a deficit of rapid rotators in dense regions for the youngest groups, suggesting fewer such binaries or early disruption in crowded environments, while older groups show a reversal consistent with mass segregation driving binaries toward denser cluster centers. The results imply environment- and age-dependent formation and dynamical processing of intermediate-separation binaries, though they remain preliminary and require follow-up confirmation of the binary nature of the rapid rotators.

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 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.
Paper Structure (10 sections, 3 figures)

This paper contains 10 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Data
  3. Initial selection
  4. Contamination
  5. Stellar density
  6. Results
  7. Discussion
  8. Implication on the initial likelihood of forming binaries with intermediate separations in different environments
  9. Evolution of the distribution of binaries with intermediate separations with age
  10. Conclusions

Figures (3)

  • Figure 1: Comparison of angular momentum difference of stars in Orion between the data and the model, highlighting the sources that have been previously identified as rapid rotators in this region.
  • Figure 2: Fraction of rapid rotators as function of fourth nearest neighbor distance in each of the moving groups used in the analysis. Smaller distance to the fourth nearest neighbor translate to higher density. The best fitted slope is shown with the dashed line. Only bins with at least 5 rapid rotators are shown. Red line shows the full sample, blue line shows only the sample where periods have been confirmed with TESS_localize. The plot shows younger populations having a more positive slope, i.e., more rapid rotators are found in the more diffuse regions. On the other hand, older populations have a more negative slope, i.e., more rapid rotators are found in denser parts of the population.
  • Figure 3: Evolution of slopes of the fraction of rapid rotators as a function of density shown in Figure \ref{['fig:fractions']} relative to the age of each population.