Mapping the Northern Galactic Disk Warp with Classical Cepheids
  We present an updated three dimensional map of the Milky Way based on a
sample of 2431 classical Cepheid variable stars, supplemented with about 200
newly detected classical Cepheids from the OGLE survey. The new objects were
discovered as a result of a dedicated observing campaign of the ~280 square
degree extension of the OGLE footprint of the Galactic disk during 2018-2019
observing seasons. These regions cover the main part of the northern Galactic
warp that has been deficient in Cepheids so far. We use direct distances to the
sample of over 2390 classical Cepheids to model the distribution of the young
stellar population in the Milky Way and recalculate the parameters of the
Galactic disk warp. Our data show that its northern part is very prominent and
its amplitude is ~10% larger than that of the southern part. By combining Gaia
astrometric data with the Galactic rotation curve and distances to Cepheids
from our sample, we construct a map of the vertical component of the velocity
vector for all Cepheids in the Milky Way disk. We find large-scale vertical
motions with amplitudes of 10-20 km/s, such that Cepheids located in the
northern warp exhibit large positive vertical velocity (toward the north
Galactic pole), whereas those in the southern warp - negative vertical velocity
(toward the south Galactic pole).
