Evidence for CO depletion in the inner regions of gas-rich protoplanetary disks^*

¹ European Southern Observatory, Karl-Schwarzschild-Str.2, 85748 Garching bei München, Germany
² Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands e-mail: g.vanderplas@uva.nl
³ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁴ ISDC Data Centre for Astrophysics, Ch. d'Ecogia 16, 1290 Versoix, Switzerland
⁵ Observatoire de Genève, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
⁶ Institute for Astrophysics, Radbout University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received: 13 October 2008
Accepted: 17 April 2009

Abstract

Aims. We investigate the physical properties and spatial distribution of Carbon Monoxide (CO) gas in the disks around the Herbig Ae/Be stars HD 97048 and HD 100546.

Methods. Using high-spectral-resolution 4.588-4.715 μm spectra containing fundamental CO emission taken with CRIRES on the VLT, we probe the circumstellar gas and model the kinematics of the emission lines. By using spectro-astrometry on the spatially resolved targets, we constrain the physical size of the emitting regions in the disks.

Results. We resolve, spectrally and spatially, the emission of the ¹³CO v(1-0) vibrational band and the ¹²CO , , and  vibrational bands in both targets, as well as the ¹²CO  band in HD 100546. Modeling of the CO emission with a homogeneous disk in Keplerian motion, yields a best fit with an inner and outer radius of the CO emitting region of 11 and 100 AU for HD 97048. HD 100546 is not fit well with our model, but we derive a lower limit on the inner radius of 8 AU. The fact that gaseous [OI] emission was previously detected in both targets at significantly smaller radii suggests that CO may be effectively destroyed at small radii in the surface layers of these disks.