The Far-Ultraviolet Spectra of TW Hydrae. II. Models of H2 Fluorescence in a Disk

By G. Herczeg, B. Wood, J. Linsky, J. Valenti, C. Johns–Krull. 2004

172 citations recorded by the source corpus.

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 H2 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 H2. We simulate a one-dimensional plane-parallel atmosphere to estimate fluxes for the 140 observed H2 emission lines and to reconstruct the Lyα 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 Lyα 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, a temperature T = 2500 K, and a filling factor of H2, 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8719fdf4c591540f7a25ee24b437620e18fabca7

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. D. Wilner
2. S. Andrews
3. Fred C. Adams
4. G. Herczeg
5. A. Hughes
6. E. Bergin
7. D. Hollenbach
8. U. Gorti

Citations in the corpus

• PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR (2008, background): “…and scaling with mass. FUV luminosities of stars are observationally well studied (e.g., IUE, Valenti et al. 2003; FUSE, Bergin et al. 2003; Herczeg et al. 2004) and theoretically believed to arise due to both activity in the chromosphere and accretion hot spots on the surface of the star.”
• The Sun in Time: Activity and Environment (2007, background): “…radial velocities, an origin of the fluorescence in a hydrogenic surface layer of the inner accretion disk at temperatures of 2000– 3500K is likely (Herczeg et al., 2002, 2004) although significantly blueshifted H2 emission points to outflow-related fluorescence in some systems (Brown et al.,…”
• EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, methodology): “For the input stellar UV field, we adopt the observed spectrum of TW Hya (Figure 2; Herczeg et al. 2002, 2004).”
• Turbulence in the TW Hya Disk (2018, result): “This accretion limit is also consistent with the measured accretion rate onto the star (2×10−9 M yr−1; Alencar & Batalha 2002; Herczeg et al. 2004; Ingleby et al. 2013).”
• Young Stars Near the Sun (2004, background): “A model of the H2 fluorescence suggests that the emitting molecules reside in a warm (∼2500 K) surface layer of the disk within ∼2 AU of TW Hya (Herczeg et al. 2004).”
• Heating Protoplanetary Disk Atmospheres (2004, background): “Recent studies have begun to investigate the role of Ly photons in the surface excitation of the inner disk (Herczeg et al. 2002, 2004), as well as in the chemistry of the outer disk (Bergin et al. 2003).”
• THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS (2012, background): “H2 fluorescence lines are also powerful diagnostics of the molecular surface layers of protoplanetary disks over a similar range of temperatures (Herczeg et al. 2004; France et al. 2012b).”
• TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR (2009, background): “FUV FUV luminosities of stars are well-studied observationally (e.g., IUE, Valenti et al. 2003; FUSE, Bergin et al. 2003, Herczeg et al. 2004) and theoretically believed to arise due to both activity in the chromosphere and accretion hotspots on the surface of the star.”
• UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs (2008, background): “For TW Hya, X-ray and UV lines account for ∼ 30 − 45% of the total accretion flux, most of which is in H I Lyα, but most have fluxes that when summed are likely < 20% of the accretion flux (Kastner et al. 2002; Herczeg et al. 2004).”