Kinematics of the circumstellar gas around UXOR stars

This thesis presents the results of a high spectral resolution study of the circumstellar (CS) gas around the intermediate mass, pre-main sequence UXOR stars BF Ori, SV Cep, UX Ori, WW Vul and XY Per. The results are based on a set of 38 echelle spectra covering the spectral range 3800-5900 Angstroms, monitoring the stars on time scales of months, days and hours. All spectra show a large number of Balmer and metallic lines with variable blueshifted and redshifted absorption features superimposed to the photospheric stellar spectra. Synthetic Kurucz models are used to estimate rotational velocities, effective temperatures and gravities of the stars. The best photospheric models are subtracted from each observed spectrum to determine the variable absorption features due to the circumstellar gas; those features are characterized, via multigaussian fitting, in terms of their velocity, v, dispersion velocity, Delta_v, and residual absorption, R_max. The absorption components detected in each spectrum can be grouped by their similar radial velocities and are interpreted as the signature of the dynamical evolution of gaseous clumps. Most of the events undergo accelerations/decelerations at a rate of tenths of ms-2. The typical timescale for the duration of the events is a few days. The dispersion velocity and the relative absorption strength of the features do not show drastic changes during the lifetime of the events, which suggests that they are gaseous blobs preserving their geometrical and physical identity. See full abstract in the document