2001/10/18 by D. R. Ardila, G. Basri, Gibor Basri +5 · 3 citations
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Context (archaeology) #Emission spectrum #Excited state #Galaxy #Line (geometry) #Magnetosphere #Outflow #Physics #Plasma #Redshift #Spectral line #Stars #Stellar, planetary, and galactic studies #T Tauri star #astro-ph
paper · pdf · doi:10.1086/338223
67 pages, 19 figures, Accepted in ApJ
arxiv created 2001/10/18 · openalex publication_date 2002/02/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges 40 A wide centered on 1345, 1400, 1497, 1550, and 1900 A. These UV spectra show strong SiIV, and CIV emission, and large quantities of sharp (~40 km/s) H2 lines. All the H2 lines belong to the Lyman band and all the observed lines are single peaked and optically thin. The averages of all the H2 lines centroids for each star are negative which may indicate that they come from an outflow. We interpret the emission in H2 as being due to fluorescence, mostly by Lyalpha, and identify seven excitation routes within 4 A of that line. We obtain column densities (1012 to 1015 cm-2) and optical depths (~1 or less) for each exciting transition. We conclude that the populations are far from being in thermal equilibrium. We do not observe any lines excited from the far blue wing of Lyalpha, which implies that the molecular features are excited by an absorbed profile. SiIV and CIV (corrected for H2 emission) have widths of ~200 km/s, and an array of centroids (blueshifted lines, centered, redshifted). These characteristics are difficult to understand in the context of current models of the accretion shock. For DR Tau we observe transient strong blueshifted emission, perhaps the a result of reconnection events in the magnetosphere. We also see evidence of multiple emission regions for the hot lines. While CIV is optically thin in most stars in our sample, SiIV is not. However, CIV is a good predictor of SiIV and H2 emission. We conclude that most of the flux in the hot lines may be due to accretion processes, but the line profiles can have multiple and variable components.