The Far-Ultraviolet Spectrum of TW Hydrae. I. Observations of H2 Fluorescence

By G. Herczeg, J. Linsky, J. Valenti, C. Johns–Krull, B. Wood. 2002

179 citations recorded by the source corpus.

We observed the classical T Tauri star TW Hya with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST) using the E140M grating, from 1150 to 1700 Å, with the E230M grating, from 2200 to 2900 Å, and with the Far Ultraviolet Spectroscopic Explorer from 900 to 1180 Å. Emission in 146 Lyman-band H2 lines, representing 19 progressions, dominates the spectral region from 1250 to 1650 Å. The total H2 emission line flux is 1.94 × 10-12 ergs cm-2 s-1, which corresponds to 1.90 × 10-4 L☉ at TW Hya's distance of 56 pc. A broad stellar Lyα line photoexcites the H2 from excited rovibrational levels of the ground electronic state to excited electronic states. The C II λ1335 doublet, C III λ1175 multiplet, and C IV λ1550 doublet also electronically excite H2. The velocity shift of the H2 lines is consistent with the photospheric radial velocity of TW Hya, and the emission is not spatially extended beyond the 0.″05 resolution of HST. The H2 lines have an intrinsic FWHM of 11.91 ± 0.16 km s-1. One H2 line is significantly weaker than predicted by this model because of C II wind absorption. We also do not observe any H2 absorption against the stellar Lyα profile. From these results we conclude that the H2 emission is more consistent with an origin in a disk rather than in an outflow or circumstellar shell. We also analyze the hot accretion region lines (e.g., C IV, Si IV, O VI) of TW Hya, which are formed at the accretion shock, and discuss some reasons why Si lines appear significantly weaker than other TR region lines.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e5850f9255b74f8e2f80e309d902735a7172b03f

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Citations in the corpus

Heating Protoplanetary Disk Atmospheres (2004, methodology): “Thus, the TW Hya system poses interesting future challenges for our model and suggests the need for a more self-consistent density structure and potentially new heating and ionization sources.”
Young Stars Near the Sun (2004, background): “Also, H2 fluorescent UV emission in Lyman band transitions has been seen by HST/STIS, but in this case the excited electronic state is pumped mainly by H2 transitions coincident with Lyα (Herczeg et al. 2002).”
Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546 (2016, background): “…of the UV spectrum of gas accreting onto TW Hya have found the [C iv]/[Si iv] ratio to be about an order of magnitude higher than in most other T Tauri stars, possibly owing to the accretion of silicon-poor (carbon-rich) material (e.g. Ardila et al. 2002; Herczeg et al. 2002; Ardila et al. 2013).”
The Sun in Time: Activity and Environment (2007, background): “…unresolved FUV fluorescence lines of H2 have been detected from several CTTS (Brown et al., 1981; Valenti et al., 2000; Ardila et al., 2002; Herczeg et al., 2002, 2006), but usually not from WTTS (Valenti et al., 2000); this emission is reprocessed stellar Lyα emission most intensely…”
Probing T Tauri Accretion and Outflow with 1 Micron Spectroscopy (2006, background): “…and broad emission sometimes accompanied by redshifted absorption below the continuum and/or narrow centered emission, are attributed to formation in magnetospheric funnel flows and accretion shocks on the stellar surface (Edwards et al. 1994; Muzerolle et al. 2001; Herczeg et al. 2002, 2005).”
Gas in the Terrestrial Planet Region of Disks: CO Fundamental Emission from T Tauri Stars (2003, background): “For example, the H2 emission from DF Tau has an FWHMof 25 km s 1 (Herczeg et al. 2002), much narrower than the 70 km s 1 width found for the CO fundamental lines from this source.”
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).”