An Asymmetric Keplerian Disk Surrounding the O-type Protostar
  IRAS16547$-$4247
  During the last decades, a great interest has emerged to know if even the
most massive stars in our galaxy (namely the spectral O-type stars) are formed
in a similar manner as the low- and intermediate-mass stars, that is, through
the presence of accreting disks and powerful outflows. Here, using sensitive
observations of the Atacama Large Millimeter/Submillimeter Array (ALMA), we
report a resolved Keplerian disk (with fifteen synthesized beams across its
major axis) surrounding the deeply embedded O-type protostar IRAS16547$-$4247.
The disk shows some asymmetries that could arise because of the disk is
unstable and fragmenting or maybe because of different excitation conditions
within the disk. The enclosed mass estimated from the disk Keplerian radial
velocities is 25$\pm$3 M$_\odot$. The molecular disk is at the base of an
ionized thermal radio jet and is approximately perpendicular to the jet axis
orientation. We additionally find the existence of a binary system of compact
dusty objects at the center of the accreting disk, which indicates the possible
formation of an O-type star and a companion of lower mass. This is not
surprising due to the high binary fraction reported in massive stars.
Subtracting the contribution of the dusty disk plus the envelope and the
companion, we estimated a mass of 20 M$_\odot$ for the central star.
