High-resolution Ultraviolet Radiation Fields of Classical T Tauri Stars

Abstract

The far-ultraviolet (FUV; 912--1700 Å) radiation field from accreting central stars in Classical T Tauri systems influences the disk chemistry during the period of giant planet formation. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly$\alpha$ emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly$\alpha$ line profiles and remove atomic and molecular disk emission (from H${}_2$ and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly$\alpha$, \ion{N}{5}, \ion{C}{4}, \ion{He}{2}) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical Classical T Tauri Star FUV radiation field at 1 AU from the central star is $\sim$ 10${}^7$ times the average interstellar radiation field. The Ly$\alpha$ emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly$\alpha$ flux are strongly correlated with \ion{C}{4} flux, suggesting that accretion processes dominate the production of both of these components. On average, only $\sim$ 0.5% of the total FUV flux is emitted between the Lyman limit (912 Å) and the H${}_2$ (0 -- 0) absorption band at 1110 Å. The total and component-level high-resolution radiation fields are made publicly available in machine-readable format.

22 pages, 15 figures. Accepted to ApJ. On-line data at http://cos.colorado.edu/~kevinf/ctts_fuvfield.html

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