Constraining the Galactic Bar and Spiral Pattern Speeds with the Hyades Tidal Stream

Abstract We present a suite of direct N -body simulations of the Hyades open cluster and its tidal stream in a Milky Way potential that includes a rotating bar and spiral arms. Using the high-resolution code PETAR and an AGAMA -based multicomponent Galactic model, we vary the bar and spiral pattern speeds (Ω b , Ω s ) on a discrete grid and quantify the resulting changes in stream orientation, length, and internal density structure. We compare the simulations to Gaia EDR3 using the convergent point and compact convergent point methods, followed by an adaptive three-dimensional nearest-neighbor matching in Cartesian space ( x , y , z ). The Gaia candidate members exhibit a pronounced longitudinal density peak at Y rot ≈ 0.1 kpc in a stream-aligned coordinate system. Models with Ω s = 22.5 km s −1 kpc −1 and Ω b ≃ 40–45 km s −1 kpc −1 best reproduce this feature, while models with a faster bar fail to match the observed density structure. These models are consistent with recent constraints favoring a relatively slow Galactic bar, and they illustrate how nearby open-cluster streams can provide an independent, local constraint on nonaxisymmetric Galactic dynamics.