Letter to the Editor

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

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 (). A high resolving power () spectrum was obtained with the infrared spectrometer ISAAC mounted on . Modeling of the profile suggests that the hot ( K) and dense ( 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 ( 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.