Local Kinematics and the Local Standard of Rest

Local Kinematics and the Local Standard of Rest

18 December 2009 | Ralph Schönhrich, James Binney, Walter Dehnen
The authors re-examine the stellar kinematics of the Solar neighborhood, focusing on the Sun's velocity $\boldsymbol{v}_{\odot}$ relative to the Local Standard of Rest (LSR). They critique the classical method of determining the component $V_{\odot}$ in the direction of Galactic rotation, which relies on Strömberg's relation and assumes a linear relationship between mean heliocentric azimuthal velocity and velocity dispersion. This method is shown to be unreliable due to the metallicity gradient in the disc, which introduces a correlation between star color and radial gradients of properties. The authors use a chemodynamical model (Schönrich & Binney, 2009a) to fit the velocity distribution of stars in the Solar neighborhood, obtaining a new value for $(U, V, W)_{\odot} = (11.1_{-0.75}^{+0.69}, 12.24_{-0.47}^{+0.47}, 7.25_{-0.36}^{+0.37})$ km s$^{-1}$, with systematic uncertainties of $\sim (1, 2, 0.5)$ km s$^{-1}$. They find that $V_{\odot}$ is 7 km s$^{-1}$ larger than previously estimated, and this new value is insensitive to the metallicity gradient within the disc. The paper highlights the importance of considering the complex kinematics of stars near the Solar neighborhood, particularly in regions with significant age and metallicity gradients.The authors re-examine the stellar kinematics of the Solar neighborhood, focusing on the Sun's velocity $\boldsymbol{v}_{\odot}$ relative to the Local Standard of Rest (LSR). They critique the classical method of determining the component $V_{\odot}$ in the direction of Galactic rotation, which relies on Strömberg's relation and assumes a linear relationship between mean heliocentric azimuthal velocity and velocity dispersion. This method is shown to be unreliable due to the metallicity gradient in the disc, which introduces a correlation between star color and radial gradients of properties. The authors use a chemodynamical model (Schönrich & Binney, 2009a) to fit the velocity distribution of stars in the Solar neighborhood, obtaining a new value for $(U, V, W)_{\odot} = (11.1_{-0.75}^{+0.69}, 12.24_{-0.47}^{+0.47}, 7.25_{-0.36}^{+0.37})$ km s$^{-1}$, with systematic uncertainties of $\sim (1, 2, 0.5)$ km s$^{-1}$. They find that $V_{\odot}$ is 7 km s$^{-1}$ larger than previously estimated, and this new value is insensitive to the metallicity gradient within the disc. The paper highlights the importance of considering the complex kinematics of stars near the Solar neighborhood, particularly in regions with significant age and metallicity gradients.
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