2005A&A...436..977C

We present the results of medium-resolution spectroscopy of five nearby Herbig Ae/Be stars at 4.7µm: 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 5σ upper limit of <10^–12cm^–2 to the column density of hot CO (T≃1500K) 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 ν=1-0 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 50AU of their disks.