# Trojans in the Solar Neighborhood

## TL;DR

This paper investigates whether the Hercules stream in the solar neighborhood could be composed of stellar trojans captured at the L4 Lagrangian point of the galactic bar, using high-resolution N-body simulations to analyze their dynamics.

## Contribution

It demonstrates that stellar trojans at L4 can explain the Hercules stream's velocity asymmetry and provides testable predictions for Gaia data to confirm this origin.

## Key findings

- Trojans cause the velocity asymmetry in Hercules.
- Trojans are only temporarily captured at L4 before escaping.
- The Hercules stream's distribution can be explained by trojan dynamics.

## Abstract

About 20% of stars in the solar vicinity are in the Hercules stream, a bundle of stars that move together with a velocity distinct from the Sun. Its origin is still uncertain. Here, we explore the possibility that Hercules is made of trojans, stars captured at L4, one the Lagrangian points of the stellar bar. Using GALAKOS--a high-resolution N-body simulation of the Galactic disk--we follow the motions of stars in the co-rotating frame of the bar and confirm previous studies on Hercules being formed by stars in co-rotation resonance with the bar. Unlike previous work, we demonstrate that the retrograde nature of trojan orbits causes the asymmetry in the radial velocity distribution, typical of Hercules in the solar vicinity. We show that trojans remain at capture for only a finite amount of time, before escaping L4 without being captured again. We anticipate that in the kinematic plane the Hercules stream will de-populate along the bar major axis and be visible at azimuthal angles behind the solar vicinity with a peak towards L4. This test can exclude the OLR origin of the Hercules stream and be validated by Gaia DR3 and DR4.