Gaps and Rings in an ALMA Survey of Disks in the Taurus Star-forming
  Region
  Rings are the most frequently revealed substructure in ALMA dust observations
of protoplanetary disks, but their origin is still hotly debated. In this
paper, we identify dust substructures in 12 disks and measure their properties
to investigate how they form. This subsample of disks is selected from a
high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus
star-forming region, which was designed to cover a wide range of sub-mm
brightness and to be unbiased to previously known substructures. While
axisymmetric rings and gaps are common within our sample, spiral patterns and
high contrast azimuthal asymmetries are not detected. Fits of disk models to
the visibilities lead to estimates of the location and shape of gaps and rings,
the flux in each disk component, and the size of the disk. The dust
substructures occur across a wide range of stellar mass and disk brightness.
Disks with multiple rings tend to be more massive and more extended. The
correlation between gap locations and widths, the intensity contrast between
rings and gaps, and the separations of rings and gaps could all be explained if
most gaps are opened by low-mass planets (super-Earths and Neptunes) in the
condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not
well correlated with the expected locations of CO and N$_2$ ice lines, so
condensation fronts are unlikely to be a universal mechanism to create gaps and
rings, though they may play a role in some cases.
