Determining the Galactic Bar Parameters based on the Hercules and Wolf 630 Stellar Streams

TL;DR

This study analyzes stellar streams in the solar neighborhood to determine the Galactic bar's pattern speed and orientation by modeling resonant orbits, suggesting a common bar-induced origin for the streams.

Contribution

It introduces a method to estimate Galactic bar parameters independently from stellar streams using resonant orbit analysis, providing new constraints on the bar's properties.

Findings

Bar pattern speed is 45-52 km/s/kpc, mean 48.1 km/s/kpc.

Bar angle is 35-65 degrees, mean 50 degrees.

Streams likely formed by long-term bar influence causing UV velocity splitting.

Abstract

We have identified the four most significant features in the UV velocity distribution of solar neighborhood stars: H1,H2 and W1,W2 in the Hercules and Wolf 630 streams respectively. We have put the task of determining number of characteristics of the central Galactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams have 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 \Omega_b lies within the range 45-52 km/s/kpc with a mean of 48.1+/-1.0 km/s/kpc, while the bar angle \theta_b is within the range 35-65 degrees with a mean of 50+/-4 degrees. The results obtained are consistent with the view that the Hercules and Wolf 630 streams could be formed by a single mechanism associated with the fact that a long-term influence of the Galactic bar led to a characteristic bimodal splitting of the UV velocity plane.