An Asymmetric Keplerian Disk Surrounding the O-type Protostar IRAS 16547−4247

Abstract

Abstract For the past few decades, there has been great interest in determining 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, we report a resolved Keplerian disk (with 15 synthesized beams across its major axis) surrounding the deeply embedded O-type protostar IRAS 16547−4247. The disk shows some asymmetries that could arise because the disk is unstable and fragmenting or because of different excitation conditions within the disk. The enclosed mass estimated from the disk Keplerian radial velocities is 25 ± 3 M ⊙. 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 ⊙ for the central star.