Evidence for an inner molecular disk around massive Young Stellar Objects

Free access article

Issue		A&A Volume 427, Number 3, December I 2004


Page(s)		L13 - L16
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200400088

A&A 427, L13-L16 (2004)
DOI: 10.1051/0004-6361:200400088

Letter

Evidence for an inner molecular disk around massive Young Stellar Objects

A. Bik and W. F. Thi

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 $\Delta v = 30$ 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 $4 \times 10^{21}$ 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 ( $n_{\rm H}>10^{10}$ cm ^-3) inner disks may be relatively common at an advanced stage of high-mass star formation.

Key words: stars: early-type, formation -- circumstellar matter -- molecular processes -- line: profiles

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