Ae / Be Stars

We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars in a search for the [O i] 6300.2 ˚ A line. The vast majority of the stars in our sample show narrow (FWHM < 100 km s −1) emission lines, centered on the stellar radial velocity. Some stars in our sample show double-peaked lines profiles, with peak-to-peak separations of ∼ 10 km s −1. The presence and strength of the [O i] line emission appears to be well correlated with the far-infrared energy distribution of each source: stars with a strong excess at 60 µm have in general stronger [O i] emission than stars with weaker 60 µm excesses. We interpret the [O i] 6300.2 ˚ A line profiles as arising in the surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars. 1 Observations High-resolution optical spectra of 49 Herbig Ae/Be stars were obtained with the Coudé Echelle Spectrograph (R = 130,000) on the ESO 3.6 m telescope, the Echelle spectrograph on the Mayall 4m telescope at KPNO (R = 30,000) and the Utrecht Echelle Spectrograph on the William Herschel Telescope (R = 45,000). The spectra were examined for the presence of the [O i] 6300.2 ˚ A line – the strongest forbidden emission line at optical wavelengths. We detect [O i] 6300.2 ˚ A in emission in 39 out of the 49 sources in our sample. The vast majority of these sources show narrow (FWHM < 100 km s −1) profiles, centered on the stellar radial velocity or slightly blue-shifted (centroid position up to −70 km s −1). In only three sources in which [O i] emission was detected, the feature is much broader (∼ 400 km s −1) and strongly blue-shifted (∼ −200 km s −1) with respect to the stellar radial velocity. A more careful inspection of the centroid velocities of the detected [O i] emission lines shows that the vast majority of Herbig Ae/Be stars have centroid velocities that are close to the stellar radial velocity. Nevertheless, there appears to be a small minority of Herbig stars that show slightly (up to −70 km s −1) blue-shifted centroid velocities as well (Fig. 2).