Flare and Warp of Galactic Disk with OB Stars from Gaia DR2

The OB stars are selected from the Gaia DR2 catalog to explore the flare and warp of the Galactic disk in this work. The Gaia and 2MASS photometric information is adopted as the criteria to choose the sample stars. We model the Galactic disk stellar distribution in this work taking the flare and warp into consideration. The parameters in the flare and warp model are acquired directly by fitting the stars with the stellar distribution function of the disk. We obtain that the scale length of the Galactic disk in space density is 2.10 +/- 0.01 kpc. We find that the disk scale height increases with Galactic radius via fitting our sample stars perpendicular to the Galactic plane. The scale height of OB stars increases more moderately than old stellar populations in the disk. It is also concluded that the inner disk is flat and begins to warp at about 9 kpc away from Galactic center. The warp amplitude of OB stars is similar to pulsars and slowly increases along the Galactic radius.