H-ALPHA EMISSION IN PRE-MAIN-SEQUENCE STARS .1. AN ATLAS OF LINE-PROFILES

We present an atlas of very high resolution (R similar to 50000) H alp ha line profiles of 63 pre-main sequence stars, divided among 43 T Tau ri stars, 18 Herbig Ae/Be stars, and 2 FU Orionis objects. Her emissio n is the most common and prominent spectroscopic feature of pre-main s equence stars, and although it is optically very thick it is still the most frequently modelled emission line in young stars. In T Tauri sta rs the principal models involve magnetically driven winds, and more re cently the role of infalling magnetospheric material has been explored . For Herbig Ae/Be stars a variety of models have been proposed, curre nt emphasis is directed towards obscuration by clumpy circumstellar di sk structures. In order to provide constraints on such models, we have made a statistical analysis of the 63 high resolution profiles. We he re ignore the considerable variability of the H alpha emission, which is discussed in detail in a second paper. Most of our observed lines s how complex profiles due to an interplay between emission and absorpti on features, and we suggest a two-dimensional classification scheme to describe these line profiles, based on the relative height of a secon dary peak to the primary peak, as well as whether the absorption is bl ue- or red-shifted. Among T Tauri stars, 25% have symmetric profiles, 49% have blueshifted absorption dips, and 5% have P Cygni profiles; th e remaining 21% show a variety of redshifted absorptions. For Herbig A e/Be stars symmetric lines are quite rare (11%), indeed almost all of these stars have deep and prominent central absorptions. We have measu red the extent of the line wings for all of our stars at the I-max/40 level, and find that almost all have very extended wings, with typical extents of +/-350 km/s, but in high S/N spectra the wings can be trac ed to lower intensities, and velocities as high as +/-900 km/s have be en observed. Pronounced asymmetries of these extended wings are found for many stars, suggesting the possibility that the highest velocity m aterial could be non-uniformly distributed. The equivalent widths of t he Bo emission in our sample of stars span two orders of magnitude, wi th a distribution that increases with decreasing equivalent width.