HAMILTON ECHELLE SPECTRA OF YOUNG STARS .2. TIME-SERIES ANALYSIS OF H-ALPHA VARIATIONS

We present the results of time series analysis on the Hα profile variations in 7 T Tauri stars (TTS). All stars show strong line profile variability. Included in the data are 37 almost fully contiguous nights of profile data on 5 TTS. For these stars (T Tau, RY Tau, DF Tau, DR Tau, and RW Aur) our temporal sampling is adequate to look for periodicities. We detect periodic variations on the red side of the profile near the peak of the line in two of our stars (7.3 days in DF Tau and 5.1 days in DR Tau). The periods recovered and the location in the line profiles displaying the periodicity do not provide the convincing support for magnetocentrifugally controlled accretion and wind generation which SU Aur exhibited. The other stars show no evidence for periodic profile behavior. Correlation analysis shows that the blue-shifted absorption component of the line profile visible in most of these stars varies on a longer time scale and is basically uncorrelated with the rest of the line profiles. We interpret this as evidence for this feature forming far from the star and that the velocity of this feature indicates the terminal velocity of the flow from TTS seen in Hα, which is substantially below escape velocity. We find that TTS Hα profile variations are not due to global changes in the physical parameters of the wind and accretion flows surrounding these stars but instead represent smaller-scale stochastic variability. Changes in the profiles tend to occur in discrete velocity patches rather than across the whole line. Over most of the profile the time scale for this tends to be less than two days. While of the general nature of a "stochastic wind," the variations differ substantially in detail from a model which has been proposed for this. A new result is the common appearance of variance peaks on the red side of Hα as well. These peaks are likely indirect evidence of variable accretion seen in this line, which rarely shows overt red-shifted absorption. © 1995 American Astronomical Society.