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

Abstract

We 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 set the task of determining a number of characteristics of the central Galactic bar independently by analyzing each of the identified features under the assumption that the Hercules and Wolf 630 streams have a bar-induced dynamical nature. We solve the problem by constructing 2 : 1 resonant orbits in the rotating bar frame for each star in these streams. Our analysis of the resonant orbits found has shown that the bar pattern speed Ωb lies within the range 45–52 km s−1 kpc−1 with a mean of 48.1±1.0 km s−1 kpc−1, while the bar angle θb is within the range 35° – 65° with a mean of 50 ± 4°. 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.

Keywords

• stars: kinematics and dynamics
• galaxy: fundamental parameters
• galaxy: kinematics and dynamics
• solar neighborhood
• stellar streams: individual (hercules stream, wolf 630 stream)