Rings and Radial Waves in the Disk of the Milky Way
  We show that in the anticenter region, between Galactic longitudes of
$110^\circ<l<229^\circ$, there is an oscillating asymmetry in the main sequence
star counts on either side of the Galactic plane using data from the Sloan
Digital Sky Survey. This asymmetry oscillates from more stars in the north at
distances of about 2 kpc from the Sun to more stars in the south at 4-6 kpc
from the Sun to more stars in the north at distances of 8-10 kpc from the Sun.
We also see evidence that there are more stars in the south at distances of
12-16 kpc from the Sun. The three more distant asymmetries form roughly
concentric rings around the Galactic center, opening in the direction of the
Milky Way's spiral arms. The northern ring, 9 kpc from the Sun, is easily
identified with the previously discovered Monoceros Ring. Parts of the southern
ring at 14 kpc from the Sun (which we call the TriAnd Ring) have previously
been identified as related to the Monoceros Ring and others have been called
the Triangulum Andromeda Overdensity. The two nearer oscillations are
approximated by a toy model in which the disk plane is offset by of the order
100 pc up and then down at different radii. We also show that the disk is not
azimuthally symmetric around the Galactic anticenter and that there could be a
correspondence between our observed oscillations and the spiral structure of
the Galaxy. Our observations suggest that the TriAnd and Monoceros Rings (which
extend to at least 25 kpc from the Galactic center) are primarily the result of
disk oscillations.
