ALMA 690 GHz observations of IRAS 16293-2422B: Infall in a highly
  optically-thick disk
  We present sensitive, high angular resolution ($\sim$ 0.2 arcsec)
submillimeter continuum and line observations of IRAS 16293-2422B made with the
Atacama Large Millimeter/Submillimeter Array (ALMA). The 0.45 mm continuum
observations reveal a single and very compact source associated with IRAS
16293-2422B. This submillimeter source has a deconvolved angular size of about
400 {\it milli-arcseconds} (50 AU), and does not show any inner structure
inside of this diameter. The H$^{13}$CN, HC$^{15}$N, and CH$_{3}$OH line
emission regions are about twice as large as the continuum emission and reveal
a pronounced inner depression or "hole" with a size comparable to that
estimated for the submillimeter continuum. We suggest that the presence of this
inner depression and the fact that we do not see inner structure (or a flat
structure) in the continuum is produced by very optically thick dust located in
the innermost parts of IRAS 16293-2422B. All three lines also show pronounced
inverse P-Cygni profiles with infall and dispersion velocities larger than
those recently reported from observations at lower frequencies, suggesting that
we are detecting faster, and more turbulent gas located closer to the central
object. Finally, we report a small east-west velocity gradient in IRAS
16293-2422B that suggests that its disk plane is likely located very close to
the plane of the sky.
