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 5627 A-type stars with d < 0.6 kpc and vertical bar z vertical bar < 0.1 kpc, selected from the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) 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-circle dot, V-circle dot, W-circle dot) = (11.69 +/- 0.68, 10.16 +/- 0.51, 7.67 +/- 0.10) km s(-1) and Oort constants A = 16.31 +/- 0.89 km s(-1) kpc(-1), B = -11.99 +/- 0.79 km s(-1) kpc(-1), C = -3.10 +/- 0.48 km s(-1) kpc(-1), and K = -1.25 +/- 1.04 km s(-1) kpc(-1). vertical bar K + C vertical bar > 4kms(-1) kpc(-1) means that there is a radial velocity gradient in the extended local disc, implying that the local disc is in a non-asymmetric potential. Using the derived Oort constants, we derive the local angular velocity Omega approximate to A - B = 28.30 +/- 1.19 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 the R-V-phi plane on constraining the solar motions and Oort constants. As the volume becomes larger towards the anticentre direction, the values of A and B become larger (implying a steeper slope of the local rotation curve) and the value of V-circle dot becomes smaller probably caused by the ridge structure and its signal increasing with distance.