THE GAS-FLOWS OF SU-AURIGAE

Series of high-resolution echelle spectra of the T Tauri star SU Aurig ae were collected during 3 observing periods. Simultaneous photoelectr ic UBV photometry was made during one period. We have analysed selecte d spectral orders, covering the Balmer lines from H alpha to H delta, He I 5876 Angstrom, the Na I D lines and Ca II 8662 Angstrom in additi on to a number of photospheric absorption lines. We confirm and extend the results found in two similar studies by Giampapa et al. (1993) an d Johns & Basri (1995). Features which have been persistent over the y ears are the simultaneous occurrence of mass infall and outflow in the line-of-sight to the star. The outflow is seen as blueshifted absorpt ion components in H alpha and H beta, but not in the higher Balmer lin es. The inflow is most evident through the redshifted absorption compo nents in the differential profiles (SU Aur minus standard) of H beta a nd the higher Balmer lines, while there is also a redshifted absorptio n-like component superimposed on the red wing of the H alpha emission. This indicates an outflow of gas in the outer part of the circumstell ar envelope/wind of the star and a simultaneous inflow/accretion in th e innermost region of the envelope. No free-fall acceleration of the i nflowing gas was found from measured accretion component velocities fr om H alpha to H delta. We found variations of the inflow velocity with an amplitude of about 50 km/s on a time-scale of 3 days, similar to t he period found earlier in the intensity variations of H alpha and H b eta. There is a correlation between the variability of the He I 5876 A ngstrom absorption line intensity and the variability in intensity of the redshifted Balmer absorption lines. This indicates that the He I l ine formation is dependent on the accretion. We identify the periodic variations with modulation of the projected inflow velocity by the ste llar rotation and find that a model with magnetically channeled accret ion in a dipole field inclined to the axis of stellar rotation describ es the observations in a natural way. SU Am is seen almost edge on. Th e time-scale of variability in the Ha blueshifted absorptions at radia l velocities of -100 to -200 km/s is less than one day. This implies a stellar wind acceleration region within 3 stellar radii and we find t hat the wind decelerates outside this region. The process of outflow i s not steady but rather impulsive, which may result in the formation o f expanding shells. The traces of such decelerated shells at large dis tance from the star are observed as a more stable blueshifted absorpti on at about -50 km/s in the profiles of the H alpha and Na I D-lines. During one period we observed a very strong event of mass ejection whe re the material was seen to decelerate over 3 days. We have also made surface (Doppler) imaging of the stellar surface using photospheric Fe I line profiles, which are variable in intensity and indicate the pre sence of stellar surface temperature inhomogeneities. The simultaneous UBV photometry provides constraints on such modeling, although due to the lack of data we do not include the photometry in the temperature mapping procedure. However, the derived temperature map is consistent with the lack of rotationally modulated variability in the B-V photome try.