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The Far-Ultraviolet Spectra of TW Hya. II. Models of H2 Fluorescence in a Disk | Gregory J. Herczeg
; Brian E. Wood
; Jeffrey L. Linsky
; Jeff A. Valenti
; Chris M. Johns-Krull
; | Date: |
10 Feb 2004 | Journal: | Astrophys.J. 607 (2004) 369-383 | Subject: | astro-ph | Abstract: | We measure the temperature of warm gas at planet-forming radii in the disk around the classical T Tauri star (CTTS) TW Hya by modelling the H2 fluorescence observed in HST/STIS and FUSE spectra. Strong Ly-alpha emission irradiates a warm disk surface within 2 AU of the central star and pumps certain excited levels of H2. We simulate a 1D plane-parallel atmosphere to estimate fluxes for the 140 observed H2 emission lines and to reconstruct the Ly-alpha emission profile incident upon the warm H2. The excitation of H2 can be determined from relative line strengths by measuring self-absorption in lines with low-energy lower levels, or by reconstructing the Ly-alpha profile incident upon the warm H2 using the total flux from a single upper level and the opacity in the pumping transition. Based on those diagnostics, we estimate that the warm disk surface has a column density of log N(H2)=18.5^{+1.2}_{-0.8}, a temperature T=2500^{+700}_{-500} K, and a filling factor of H2, as seen by the source of Ly-alpha emission, of 0.25pm0.08 (all 2-sigma error bars). TW Hya produces approximately 10^{-3} L_odot in the FUV, about 85% of which is in the Ly-alpha emission line. From the H I absorption observed in the Ly-alpha emission, we infer that dust extinction in our line of sight to TW Hya is negligible. | Source: | arXiv, astro-ph/0402238 | Services: | Forum | Review | PDF | Favorites |
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