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 $d<0.6\,\rm kpc$ and $|z|<0.1\,\rm kpc$, 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 $(U_\odot,V_\odot,W_\odot)=(11.69\pm0.68,
10.16\pm0.51, 7.67\pm0.10)\,\rm km\,s^{-1}$ and Oort constants
$A=16.31\pm0.89\,\rm km\,s^{-1}\,kpc^{-1}$, $B=-11.99\pm0.79\,\rm
km\,s^{-1}\,kpc^{-1}$, $C=-3.10\pm0.48\,\rm km\,s^{-1}\,kpc^{-1}$,
$K=-1.25\pm1.04\,\rm km\,s^{-1}\,kpc^{-1}$, respectively. $|K+C|>4\,\rm
km\,s^{-1}\,kpc^{-1}$ 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
$\Omega\,{\approx}\,A-B=28.30\pm1.19\,\rm km\,s^{-1}\,kpc^{-1}$. By using
A-type star sample of different volumes, we further try to evaluate the impacts
of the ridge pattern in $R$-$V_{\phi}$ 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.
