Hercules and Wolf 630 Stellar Streams and Galactic Bar Kinematics

TL;DR

This study analyzes stellar streams in the solar neighborhood to infer the Milky Way's bar properties, revealing the bar's pattern speed and orientation through resonant orbit modeling, supporting the bar's influence on local stellar kinematics.

Contribution

It introduces a method to determine Galactic bar characteristics independently from stellar streams by modeling resonant orbits, providing new constraints on the bar's pattern speed and angle.

Findings

Bar pattern speed is 45-55 km/s/kpc.

Bar angle is within 40-60 degrees.

Streams are likely shaped by the Galactic bar's long-term influence.

Abstract

We have identified the four most significant features in the UV velocity distribution of solar neighborhood stars: H1, H2 in the Hercules stream and W1, W2 in the Wolf 630 stream. We have formulated the problem of determining several characteristics of the central Galactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams are of a bar-induced dynamical nature. The problem has been solved by constructing 2:1 resonant orbits in the rotating bar frame for each star in these streams. Analysis of the resonant orbits found has shown that the bar pattern speed is 45-55 km/s/kpc, while the bar angle lies within the range 40-60 degrees. The results obtained are consistent with the view that the Hercules and Wolf 630 streams could be formed by a long-term influence of the Galactic bar leading to a characteristic bimodal splitting of the UV velocity plane.