Evidence for an inner molecular disk around massive Young Stellar Objects

We present observations of CO overtone bandhead emission toward four massive Young Stellar Objects (spectral type O6-B5). The high signal-to-noise ratio K-band spectra were obtained with VLT-ISAAC at a resolution Deltav=30 km s(-1), sufficient to resolve the bandheads, but not the individual J-lines. We are able to explain the shape of the lines by assuming a simple isothermal Keplerian disk model seen at different inclinations. The gas temperature ranges from 1500 to 4500 K and the CO column density is between 0.1 and 4x10(21) cm(-2). The emission probably arises within the first few astronomical units of the disk, consistent with the high gas temperature. Our results indicate that molecules can survive close to a hot star and suggest that dense (n(H)>10(10) cm(-3)) inner disks may be relatively common at an advanced stage of high-mass star formation.