The protoplanetary disc of HD 163296 as observed by ALMA
  HD 163296 is one of the few protoplanetary discs displaying rings in the dust
component. The present work uses ALMA observations of the 0.9 mm continuum
emission having significantly better spatial resolution (~8 au) than previously
available, providing new insight on the morphology of the dust disc and its
double ring structure. The disc is shown to be thin and its position angle and
inclination with respect to the sky plane are accurately measured as are the
locations and shapes that characterize the observed ring/gap structure.
Significant modulation of the intensity of the outer ring emission have been
revealed and discussed. In addition, earlier ALMA observations of the emission
of three molecular lines, CO(2-1), C18O(2-1), and DCO+(3-2), having a
resolution of ~70 au, are used to demonstrate the Keplerian motion of the gas,
found consistent with a central mass of 2.3 solar masses. An upper limit of ~9%
of the rotation velocity is placed on the in-fall velocity. The beam size is
shown to give the dominant contribution to the line widths, accounting for both
their absolute values and their dependence on the distance to the central star.
