2004A&A...427L..13B

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 Δv=30km/s, 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 4500K and the CO column density is between 0.1 and 4x10²¹cm^–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>10¹⁰cm^–3) inner disks may be relatively common at an advanced stage of high-mass star formation.