Analysis of HST ultraviolet spectra for T Tauri stars: DR Tau

We analyze the spectra of DR Tau in the wavelength range 1200 to 3100 Å obtained with the GHRS and STIS spectrographs from the Hubble Space Telescope. The profiles for the C IV 1550 and He II 1640 emission lines and for the absorption features of some lines indicate that matter falls to the star at a velocity ∼300 km s−1. At the same time, absorption features were detected in the blue wings of the N I, Mg I, Fe II, Mg II, C II, and Si II lines, suggesting mass outflow at a velocity up to 400 km s−1. The C II, Si II, and Al II intercombination lines exhibit symmetric profiles whose peaks have the same radial velocity as the star. This is also true for the emission features of the Fe II and H2 lines. We believe that stellar activity is attributable to disk accretion of circumstellar matter, with matter reaching the star mainly through the disk and the boundary layer. At the time of observations, the accretion luminosity was Lac ≃ 2L⊙ at an accretion rate ≃10−7M⊙ yr−1. Concurrently, a small (<10%) fraction of matter falls to the star along magnetospheric magnetic field lines from a height ∼R*. Within a region of size ≃3.5R*, the disk atmosphere has a thickness ∼0.1R* and a temperature ≃1.5 × 104 K. We assume that disk rotation in this region significantly differs from Keplerian rotation. The molecular hydrogen lines are formed in the disk at a distance <1.4 AU from the star. Accretion is accompanied by mass outflow from the accretion-disk surface. In a region of size <10R*, the wind gas has a temperature ∼7000 K, but at the same time, almost all iron is singly ionized by H I Lα photons from inner disk regions. Where the warm-wind velocity reaches ≃400 km s−1, the gas moves at an angle of no less than 30° to the disk plane. We found no evidence of regions with a temperature above 104 K in the wind and leave open the question of whether there is outflow in the H2 line formation region. According to our estimate, the star has the following set of parameters: M* ≃ 0.9M⊙, R* ≃ 1.8R⊙, L* ≃ 0.9L⊙, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$A_V \simeq 0\mathop .\limits^m 9$$ \end{document}. The inclination i of the disk axis to the line of sight cannot be very small; however, i≤60°.