Evidence for a hot dust-free inner disk around 51 Oph

Free access article

Issue		A&A Volume 430, Number 3, February II 2005


Page(s)		L61 - L64
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200400132

A&A 430, L61-L64 (2005)
DOI: 10.1051/0004-6361:200400132

Letter

Evidence for a hot dust-free inner disk around 51 Oph

W.-F. Thi¹, B. van Dalen¹, A. Bik^{1, 2} and L. B. F. M. Waters^{1, 3}

¹ Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Kruislaan 403 1098 SJ Amsterdam, The Netherlands
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
³ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium

(Received 29 September 2004 / Accepted 19 December 2004)

Abstract
We report on the observation of CO bandhead emission around 51 Oph ( $\Delta v=2$ ). A high resolving power ( $R\simeq10\,000$ ) spectrum was obtained with the infrared spectrometer ISAAC mounted on VLT-ANTU. Modeling of the profile suggests that the hot ( $T_{\rm gas}= 2000{-}4000$ K) and dense ( n_H>10¹⁰ cm ^-3) molecular material as probed by the CO bandhead is located in the inner AU of a Keplerian disk viewed almost edge-on. Combined with the observation of cooler gas ( $T_{\rm gas}= 500{-}900$ K) by ISO-SWS and the lack of cold material, our data suggest that the disk around 51 Oph is essentially warm and small. We demonstrate the presence of a dust-free inner disk that extents from the inner truncation radius until the dust sublimation radius. The disk around 51 Oph may be in a rare transition state toward a small debris disk object.

Key words: stars: formation -- accretion disks -- planetary systems: protoplanetary disks

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