We present Atacama Large Millimeter/submillimeter Array (ALMA) line and continuum observa- tions at 1.2mm with 0.3′′ resolution that uncover a Keplerian-like disk around the forming O-type star AFGL 4176. The continuum emission from the disk at 1.21mm (source mm1) has a deconvolved size of 870±110AU × 330±300AU and arises from a structure 8M⊙ in mass, calculated assuming a dust temperature of 190K. The first-moment maps, pixel-to-pixel line modeling, assuming local thermodynamic equilibrium (LTE), and position-velocity diagrams of the CH3CN J=13–12 K-line emission all show a velocity gradient along the major axis of the source, coupled with an increase in velocity at small radii, consistent with Keplerian-like rotation. The LTE line modeling shows that where CH3CN J=13–12 is excited, the temperatures in the disk range from 70 to at least 300K and that the H2 column density peaks at 2.8×1024 cm−2. In addition, we present Atacama Pathfinder Experiment (APEX) 12CO observations which show a large-scale outflow from AFGL 4176 perpen- dicular to the major axis of mm1, supporting the disk interpretation. Finally, we present a radiative transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and radius of 12M⊙ and 2000AU, that reproduces the line and continuum data, further supporting our conclusion that our observations have uncovered a Keplerian disk around an O-type star.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)