Letter to the Editor

Evidence for an inner molecular disk around massive Young Stellar Objects^*

Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: bik@science.uva.nl

Received: 27 May 2004
Accepted: 2 October 2004

Abstract

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  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  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 ( cm^-3) inner disks may be relatively common at an advanced stage of high-mass star formation.