SIMBAD references

Gaia DR2 data are used to calculate the Oort constants and derive the Galactic rotational properties in this work. We choose the solar vicinity stars with a "clean" sample within 500 pc. The Oort constants are then fitted through the relation between the proper motions as a function of Galactic longitude l. A maximum likelihood method is adopted to obtain the Oort constants and the uncertainties are produced by a Markov Chain Monte Carlo technique with the sample. Our results for the Oort constants are A = 15.1 ± 0.1 km s^–1 kpc^–1, B = -13.4 ± 0.1 km s^–1 kpc^–1, C = -2.7 ± 0.1 km s^–1 kpc^–1, and K = -1.7 ± 0.2 km s^–1 kpc^–1 respectively. The nonzero values of C and K represent a nonaxisymmetric model for the Galaxy. According to our results, the angular velocity Ω=|A-B|=28.5±0.1kms^–1kpc^–1 and the circular velocity decreases in solar vicinity. The local radial velocity also decreases along the radial direction due to C + K being negative.