Local Stellar Kinematics and Oort Constants from the LAMOST A-type Stars

Abstract

We estimate the solar peculiar velocities and Oort constants using a sample of 5,627 A-type stars with $d<0.6\mathrm{kpc}$ and $|z|<0.1\mathrm{kpc}$, selected from the LAMOST surveys. The radial and tangential velocities of these A-type stars are fitted by using a non-axisymmetric model. The best-fitting result yields the solar peculiar velocities $(U_{\odot },V_{\odot },W_{\odot })=(11.69\pm 0.68,10.16\pm 0.51,7.67\pm 0.10)\mathrm{km}{\mathrm{s}}^{-1}$ and Oort constants $A=16.31\pm 0.89\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$, $B=-11.99\pm 0.79\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$, $C=-3.10\pm 0.48\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$, $K=-1.25\pm 1.04\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$, respectively. $|K+C|>4\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$ means that there is a radial velocity gradient in the extended local disk, implying the local disk is in a non-asymmetric potential. Using the derived Oort constants, we derive the local angular velocity $\Omega \approx A-B=28.30\pm 1.19\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$. By using A-type star sample of different volumes, we further try to evaluate the impacts of the ridge pattern in $R$-$V_{\varphi }$ plane on constraining the solar motions and Oort constants. As the volume becomes larger toward the anti-center direction, the values of $A$ and $B$ become larger (implying a steeper slope of the local rotation curve) and the value of $V_{\odot }$ becomes smaller probably caused by the ridge structure and its signal increasing with distance.

10 pages, 10 figures, accepted for publication in MNRAS

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