The Flare and Warp of the Young Stellar Disk traced with LAMOST DR5
  OB-type stars
  We present analysis of the spatial density structure for the outer disk from
8$-$14 \,kpc with the LAMOST DR5 13534 OB-type stars and observe similar
flaring on north and south sides of the disk implying that the flaring
structure is symmetrical about the Galactic plane, for which the scale height
at different Galactocentric distance is from 0.14 to 0.5 \,kpc. By using the
average slope to characterize the flaring strength we find that the thickness
of the OB stellar disk is similar but flaring is slightly stronger compared to
the thin disk as traced by red giant branch stars, possibly implying that
secular evolution is not the main contributor to the flaring but perturbation
scenarios such as interactions with passing dwarf galaxies should be more
possible. When comparing the scale height of OB stellar disk of the north and
south sides with the gas disk, the former one is slightly thicker than the
later one by $\approx$ 33 and 9 \,pc, meaning that one could tentatively use
young OB-type stars to trace the gas properties. Meanwhile, we unravel that the
radial scale length of the young OB stellar disk is 1.17 $\pm$ 0.05 \,kpc,
which is shorter than that of the gas disk, confirming that the gas disk is
more extended than stellar disk. What is more, by considering the mid-plane
displacements ($Z_{0}$) in our density model we find that almost all of $Z_{0}$
are within 100 \,pc with the increasing trend as Galactocentric distance
increases.
