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

We estimate the solar peculiar velocities and Oort constants using a sample of 5,627 A-type stars with $d<0.6\mathrm{k}\mathrm{p}\mathrm{c}$ and $\mathrm{\mid }z\mathrm{\mid }<0.1\mathrm{k}\mathrm{p}\mathrm{c}$, 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 $(U_\odot,V_\odot,W_\odot)=(11.69\pm0.68, 10.16\pm0.51, 7.67\pm0.10),\rm km,s^{-1}$andOortconstants$A=16.31\pm0.89,\rm km,s^{-1},kpc^{-1}$,$B=-11.99\pm0.79,\rm km,s^{-1},kpc^{-1}$,$C=-3.10\pm0.48,\rm km,s^{-1},kpc^{-1}$,$K=-1.25\pm1.04,\rm km,s^{-1},kpc^{-1}$,respectively\mathrm{.}$|K+C|>4,\rm km,s^{-1},kpc^{-1}$ 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 $\mathrm{\Omega }\approx A-B=28.30\pm 1.19\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}\mathrm{k}\mathrm{p}{\mathrm{c}}^{-1}$. 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.