2004/02/10 by Gregory J. Herczeg, Brian E. Wood, Jeffrey L. Linsky +3
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Emission spectrum #Extinction (optical mineralogy) #Hubble space telescope #Line (geometry) #Opacity #Optics #Physics #Space Telescope Imaging Spectrograph #Spectral line #Spectrograph #Stars #Stellar, planetary, and galactic studies #T Tauri star #astro-ph
paper · pdf · doi:10.1086/383340
published as Astrophys.J. 607 (2004) 369-383 · Accepted by ApJ. 26 pages, 17 figures, 6 tables
arxiv created 2004/02/10 · openalex publication_date 2004/05/17 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We measure the temperature of warm gas at planet-forming radii in the disk around the classical T Tauri star (CTTS) TW Hya by modeling the H 2 fluorescence observed in Hubble Space Telescope Space Telescope Imaging Spectrograph and Far Ultraviolet Spectroscopic Explorer spectra. Strong Lyα emission irradiates a warm disk surface within 2 AU of the central star and pumps certain excited levels of H 2 . We simulate a one-dimensional plane-parallel atmosphere to estimate fluxes for the 140 observed H 2 emission lines and to reconstruct the Lyα emission profile incident upon the warm H 2 . The excitation of H 2 can be determined from relative line strengths by measuring self-absorption in lines with low-energy lower levels, or by reconstructing the Lyα profile incident upon the warm H 2 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 (H 2 ) = 18.5 , a temperature T = 2500 K, and a filling factor of H 2 , as seen by the source of Lyα emission, of 0.25 ± 0.08 (all 2 σ error bars). TW Hya produces approximately 10 -3 L ☉ in the FUV, about 85% of which is in the Lyα emission line. From the H I absorption observed in the Lyα emission, we infer that dust extinction in our line of sight to TW Hya is negligible.