A SYNOPTIC STUDY OF H-ALPHA LINE-PROFILE VARIABILITY IN THE T-TAURI STAR SU AURIGAE

We present a catalog of 106 high spectral resolution observations of t he Ha line profile in the T Tauri star SU Aurigae, obtained during the period from 1986 October through 1990 November. The spectra were acqu ired during joint synoptic programs to observe selected T Tauri stars using the Hamilton Echelle Spectrometer of the Lick Observatory and th e solar-stellar spectrograph at the McMath telescope of the National S olar Observatory on Kitt Peak. A restricted set of Mg II h and k line profiles was also obtained in a coordinated program involving the Inte rnational Ultraviolet Explorer (IUE) satellite observatory and the McM ath solar-stellar facility. Striking variability is evident on a night ly basis. A key result is that the relative intensity in the blue wing of Ha spanning a range of velocities near - 150 km s-1 is modulated a t a period of 2.98 +/- 0.4 days. We identify the 2.98 day period with the rotation period of the star. We also find that the occurrence of t he periodic modulation of the mass outflow is episodic and most eviden t during a 2 week sequence of nightly observations. We find two other intervals where the periodic spectroscopic variability is likely prese nt, although at a lower level of significance. The variability is othe rwise stochastic in nature. The Mg II resonance lines exhibit clear va riability that is most pronounced in the blue wing of the k line. A co mparison of the Mg II k line profile with Ha profiles obtained nearly simultaneously yields no apparent correlation between the variable fea tures in each line. The profile shapes of the Mg II h and k lines are generally indicative of formation in a wind. An analysis of the princi pal features that appear in the Halpha profile set suggests that the l ine is composed of contributions from an enhanced chromosphere; a rela tively slow moving, dense, optically thick component of a stellar wind formed relatively close to the star; and an optically thin, high-velo city, expanding stellar wind located further away from the star. An in vestigation of possible correlations among the principal features in t he series of Halpha profiles suggests that as the density in the wind increases, the wind may become more unstable to large turbulence. This may lead to a reduction in the wind bulk velocity, thus regulating th e mass-loss rate. We also find that the position of the main absorptio n feature which is always present in the Halpha profiles is not correl ated with its depth, indicating that optical depth and wind velocity a re not correlated in the denser portions of the wind.