Short-term variability of photospheric lines in the pre-main sequence Herbig Ae star AB Aurigae

During the multi-site MUSICOS 92 campaign, the pre-main sequence Herbig Ae star AB Aur was monitored primarily in the He I 5876 Angstrom line, but two of the telescopes were equipped with cross-dispersed echelle spectrographs. The wide spectral domain covered by these instruments allows us to study simultaneously the variability of many photospheric lines. These data are supplemented with additional observations obtained at Observatoire de Haute-Provence 2 years later. We find that the photospheric lines of AB Aur have variable profiles, and that distortions cross the line profiles from blue to red, on a time scale of a few hours. These distortions tend to extend significantly blueward of the projected rotation velocity boundary of the line. This implies that localized outflows with velocities of the order of 100 kms(-1) must be present in the photosphere and affect photospheric line formation. The photosphere of AB Aur may be affected by azimuthal structures creating the observed variability through the effect of stellar rotation, as are the overlying chromosphere and wind, although more data are needed to establish this point unambiguously.