  This paper presents an investigation of the outer disk structure by using
data from a recent release of the 2 micron sky survey (2MASS).
  This 2MASS data show unambiguously that the stellar disk thickens with
increasing distance from the Sun. In one of the field (longitude l$=$240) there
is also strong evidence of an assymetry associated with the Galactic warp. This
flaring and warping of the stellar disk is very similar to the features
observed in the HI disk. The thickening of the stellar disk explains the drop
in density observed near the Galactic plane: stars located at lower
  Galactic latitudes are re-distributed to higher latitudes. It is no longer
necessary to introduce a disk cut-off to explain the drop in density. It is
also not clear how this flaring disk is distinct from the thick disk in the
outer disk region. At least, for lines of sight in the direction of the outer
disk, the thickening of the disk is sufficient to account for the excess in
star counts attributed by some models to the thick disk.

Astrophysics