TIME-VARIABILITY ANALYSIS OF THE H-ALPHA, HE-I AND NA-I D-LINES IN THE T-TAURI STAR LKH-ALPHA-264

We present a time-series analysis of quasi-simultaneous high-resolutio n profiles of the H alpha, He I (lambda 25876 Angstrom) and Na I D lin es for the highly active T Tauri star LkH alpha 264. Our data include repeated observations on time-scales ranging from approximately 1 d do wn to less than 1 h, at two different epochs. For the three lines we h ave analysed the time variability of the equivalent width and of the p rofile, using in this case both the normalized variance and correlatio n matrix analysis. The behaviours of the equivalent widths of the He I and Na I lines on time-scales of the order of 1 d were found to corre late well. The correlation is more conspicuous when the level of varia bility of the lines is more dramatic. We conclude that there is a comm on region of formation for these lines, very close to the star. Howeve r, the H alpha equivalent width follows such behaviour only when the H e I and Na I D lines are less variable. In terms of profile variations , He I and Na I differ from Her. The He I and Na I D variations occur coherently over the entire profile, independently of the time-scales, although there are indications that such behaviour may break down for time-scales shorter than approximate to 20 min. In contrast, the varia bility of H alpha occurs mainly on the blue side of the line. Variatio ns on short time-scales seem to be associated with a secondary blue em ission peak. Variations on time-scales of id are linked to two weak bl ueshifted absorptions. These absorptions occur in an outer region and their behaviour can be understood in terms of an optical depth effect. We conclude that the Hu line is formed in two distinct regions. The i nner region, which is not too distinct from the one producing the He I and Na I D lines, is highly sensitive to the level of activity. The o uter and more extended region dominates the contribution to the flux i n H alpha when the general level of stellar activity is high.