The extreme T Tauri star RW Aur: Accretion and outflow variability

Abstract

We present an analysis of the classical T Tauri star RW Aur A, based on 77 echelle spectra obtained at Lick Observatory over a decade of observations. RW Aur, which has a higher than average mass accretion rate among T Tauri stars, exhibits permitted (Hα, Hβ, Ca II, He I, NaD) and forbidden ([OI]6300 Å) emission lines with strong variability. The permitted lines display multiple periodicities over the years, often with variable accretion (redshifted) and outflow (blueshifted) absorption components, implying that both processes are active and changing in this system. The broad components of the different emission lines exhibit correlated behavior, indicating a common origin for all of them. We compute simple magnetospheric accretion and disk-wind Hα, Hβ and NaD line profiles for RW Aur. The observed Balmer emission lines do not have magnetospheric accretion line profiles. Our modeling indicates that the wind contribution to these line profiles is very important and must be taken into account. Our results indicate that the Hα, Hβ and NaD observed line profiles of RW Aur are better reproduced by collimated disk-winds starting from a small region near the disk inner radius. Calculations were performed in a region extending out to 100 R*. Within this volume, extended winds originating over many stellar radii along the disk are not able to reproduce the three lines simultaneously. Strongly open-angled winds also generate profiles that do not look like the observed ones. We also see evidence that the outflow process is highly dynamic - the low- and high-velocity components of the [OI](6300 Å) line vary independently on timescales of days. The apparent disappearance from December 1999 to December 2000 of the [OI](6300 Å) low velocity component, which is thought to come from the disk-wind, shows that the the slow wind can exhibit dramatic variability on timescales of months (placing limits on how extended it can be). There is no comprehensive explanation yet for the behavior of RW Aur, which may in part be due to complications that would be introduced if it is actually a close binary. © ESO 2005.