A photoevaporating rotating disk in the Cepheus A HW2 star cluster.
JIMENEZ-SERRA I., MARTIN-PINTADO J., RODRIGUEZ-FRANCO A., CHANDLER C., COMITO C. and SCHILKE P.
Abstract (from CDS):
We present VLA and PdBI subarcsecond images (∼0.15"-0.6") of the radio continuum emission at 7 mm and of the SO2J=192,18⟶183,15 and J=278,20⟶287,21 lines toward the Cep A HW2 region. The SO2 images reveal the presence of a hot core internally heated by an intermediate-mass protostar, and a circumstellar rotating disk around the HW2 radio jet of size 600x100 AU and mass ∼1 M☉. Keplerian rotation for the disk velocity gradient of ∼5 km/s requires a 9 M☉ central star, which cannot explain the total luminosity observed in the region. This may indicate that the disk does not rotate with a Keplerian law due to the extreme youth of this object. Our high-sensitivity radio continuum image at 7 mm shows, in addition to the ionized jet, an extended emission to the west (and marginally to the south) of the HW2 jet, filling the southwest cavity of the HW2 disk. From the morphology and location of this free-free continuum emission at centimeter and millimeter wavelengths (spectral index ∼0.4-1.5), we propose that the disk is photoevaporating due to the UV radiation from the central star. All this indicates that the Cep A HW2 region harbors a cluster of massive stars. Disk accretion seems to be the most plausible way to form massive stars in moderate density/luminosity clusters.