Trojans in the Solar Neighborhood

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.

Submitted to ApJ. Snapshots of the simulation and animations are available upon request

References in corpus (6)

• The Structure of the Milky Way's Bar Outside the Bulge
• On the ridges, undulations & streams in Gaia DR2: Linking the topography of phase-space to the orbital structure of an N-body bar
• Tracing the Hercules stream with Gaia and LAMOST: new evidence for a fast bar in the Milky Way
• Resonances in Barred Galaxies
• Tracing Hercules in Galactic azimuth with Gaia DR2
• Kinematic structures of the Solar neighbourhood revealed by Gaia DR1/TGAS and RAVE

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