High-Resolution Studies of the Inner Circumstellar Disks of Herbig Ae/Be Stars

This thesis uses high-resolution spectroscopic data in the optical and near-infrared from the HARPS-N and GIANO instruments of a large sample of Herbig Ae/Be stars to study the inner circumstellar disk around these stars. In the first project, the optical and near-infrared HI lines of the star HD 141569 are analysed. Across all studied series, the lines show prominent, symmetric double peaks, indicative of an origin in a Keplerian pattern close to the surface of the inner disk or at the base of a disk wind. Modelling of the line profiles shows that the emission emerges very close to the central star, extending not much further out than 10 stellar radii, and reaching very close to the star. In addition, the results suggest that the lines are optically thin apart of the Halpha line close to the star. This suggests that accretion takes place in a transition zone between magnetospheric and boundary layer accretion. The second project concerns the forbidden optical emission lines of a sample of 25 Herbig Ae/Be stars. Most of their line profiles comprise a single body of emission with often prominent double peaks and velocities that are consistent with the stellar velocity. This shape also suggests an origin close to the surface of the disk, or from the base of a disk wind. The shape and detection statistic of the studied lines differ significantly from those observed towards T Tauri stars, the low-mass counterparts of Herbig Ae/Be stars. The modelling of the [OI] 6300 line profiles of ten stars shows that the emission stems from a wide range of radii, ranging from a fraction of an au for HD 141569, to over 100 au for MWC 297. It rules out an origin in a pure photoevaporative wind for most stars, and suggests an origin in a hybrid disk wind for most stars of the sample. The results for the [OI] 5577, [SII] 4068, and [SII] 6730 emission lines, the latter two only observed for the Be star HD 45677, reinforce the conclusion of an origin close to the surface of the disk.