Upper limits on CO 4.7 μm emission from disks around five Herbig Ae/Be stars

¹ European Southern Observatory, Karl Schwarzschild Strasse 2 , 75748 Garching bei München, Germany e-mail: acarmona@eso.org
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received: 25 January 2005
Accepted: 14 March 2005

Abstract

We present the results of medium-resolution spectroscopy of five nearby Herbig Ae/Be stars at 4.7 μm: UX Ori, HD 34282, HD 50138, V380 Ori, HK Ori. The goal was to search for CO fundamental ro-vibrational emission. None of the targets show CO features, either in absorption nor in emission. We derive a upper limit of <10^-12 cm^-2 to the column density of hot CO ( K) in the sources. These upper limits are considerably lower than the values of Herbig Ae/Be stars for which warm and hot CO emission has been reported. The non-detection of CO  emission in these five targets suggest that Herbig Ae/Be stars are not a homogeneous group with respect to the structure of the gaseous disk and/or the amount of CO in the inner 50 AU of their disks.