Analysis of HST Ultraviolet Spectra for T Tauri Stars: RU Lup

Abstract

The ultraviolet spectra of the star RU Lup obtained with the Hubble Space Telescope are analyzed. Emission lines are identified. The presence of absorption components with a nearly zero residual intensity in the MgII resonance doublet lines is indicative of mass outflow with a velocity V_infty = 300 km/s. These lines also exhibit a broad (1400 km/s at the base) component originating in the star itself. The profiles of the (optically thin) SiII and SiIII 1892 A lines for the first time unequivocally prove that these lines originate in an accretion shock wave rather than in the chromosphere, with the gas infall velocity being V_0 = 400 km/s. The intensity ratio of the CIV 1550 A and SiIV 1400 A resonance doublet components was found to be close to unity, suggesting a high accreted-gas density, lg N_0 > 12.5. Molecular H_2 Lyman lines formed in the stellar wind were detected. The HI L_alpha luminosity of RU Lup was found from their intensities to exceed 10% of L_bol. Radiation pressure in the L_alpha line on atomic hydrogen may play a significant role in the initial acceleration of stellar-wind matter, but the effect of L_alpha emission on the dynamics of molecular gas is negligible.