Evidence for Accretion: High-Resolution X-Ray Spectroscopy of the Classical T Tauri Star TW Hydrae

By J. Kastner, D. Huenemoerder, N. Schulz, C. Canizares, D. Weintraub. 2001

319 citations recorded by the source corpus.

We present high-resolution X-ray spectra of the X-ray-bright classical T Tauri star, TW Hydrae, covering the wavelength range of 1.5-25 Å. The differential emission measure derived from fluxes of temperature-sensitive emission lines shows a plasma with a sharply peaked temperature distribution, peaking at log T = 6.5. Abundance anomalies are apparent, with iron very deficient relative to oxygen, while neon is enhanced relative to oxygen. Density-sensitive line ratios of Ne IX and O VII indicate densities near log ne = 13. A flare with rapid (~1 ks) rise time was detected during our 48 ks observation; however, based on analysis of the emission-line spectrum during quiescent and flaring states, the derived plasma parameters do not seem strongly time-dependent. The inferred plasma temperature distribution and densities are consistent with a model in which the bulk of the X-ray emission from TW Hya is generated via mass accretion from its circumstellar disk. Assuming that accretion powers the X-ray emission, our results for log ne suggest an accretion rate of ~10-8 M☉ yr-1.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/48a99f80e5a0a743323e6c4ffcf728c7947b9a2d

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In Astronomy and Astrophysics

1. M. Gudel
2. K. Luhman
3. L. Hillenbrand
4. D. Wilner
5. S. Andrews
6. Eric Mamajek
7. G. Herczeg
8. Simon Bruderer

Citations in the corpus

• The Far-Ultraviolet Spectrum of TW Hydrae. I. Observations of H2 Fluorescence (2002, methodology): “TW Hya is a strong X-ray source, with LX 4 10 4 L as measured with Chandra by Kastner et al. (2002).”
• Accretion onto Pre-Main-Sequence Stars (2016, background): “Nonthermal ionization by stellar and accretion-driven X-rays and FUV radiation, and possibly also cosmic rays, may also allow an active MRI to develop at radii of 30 AU, although a recent ALMA study suggests that any turbulence in the outer disk may be quite weak (Flaherty et al. 2015).”
• Bright X-Ray Flares in Orion Young Stars from COUP: Evidence for Star-Disk Magnetic Fields? (2005, background): “An obvious question to ask, also in light of the recent results concerning TWHya and BP Tau, is therefore whether the different types of YSOs have different types of X-ray emitting structures (and thus of confining magnetic fields) in terms of size, location, structuring, and density.”
• The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project (2005, background): “…for this scenario (e.g., Gullbring et al. 1997), more recent high-resolution X-ray spectroscopy of some TTSs (e.g., TW Hya, XZ Tau, and BP Tau; see Kastner et al. 2002; Stelzer & Schmitt 2004; Favata et al. 2003; Schmitt et al. 2005) yielded plasma temperatures and densities that have been…”
• 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).”
• X-Ray-Irradiated Protoplanetary Disk Atmospheres. I. Predicted Emission-Line Spectrum and Photoevaporation (2008, background): “…stars are thought to produce observable X-rays: magnetospheric accretion shocks, shocks resulting from polar jets, and magnetically-confined hot coronae analogous to those found on all late-type main-sequence stars including the Sun (e.g. Kastner et al 2002, Güdel et al 2005, Walter & Kuhi, 1981).”
• TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR (2009, background): “This results in a overall spectrum somewhat similar to that observed for the soft-excess sources (Kastner et al. 2002, Stelzer & Schmitt 2004).”
• Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546 (2016, background): “The accretion luminosity is estimated to be 0.03 L , but estimates of the accretion rate vary from 4 × 10−10 to 4.8 × 10−9 M yr−1 (Muzerolle et al. 2000; Batalha et al. 2002; Kastner et al. 2002; Debes et al. 2013).”
• Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem (2005, unknown): “It is not yet clear, however, whether scaled-up solar-type activity alone can drive high enough mass loss to satisfy equation (3) (Decampli 1981; Tout & Pringle 1992; Kastner et al. 2002).”
• Toward Planetesimals in the Disk around TW Hydrae: 3.5 Centimeter Dust Emission (2005, background): “Observations of the X-ray spectrum withXMMNewton (Stelzer & Schmitt 2004) andChandra (Kastner et al. 2002) indicate electron densities 2 orders of magnitude higher than typically found in stellar coronae.”
• Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars (2004, background): “Its large Hα equivalent width is indicative of active disk accretion at a rate of ∼ 10−8 M⊙ yr−1 (Kastner et al. 2002).”
• X-ray spectroscopy of stars (2009, background): “The first suggestion for this mechanism to be at work was made by Kastner et al (2002), based on grating spectroscopy of the nearby CTTS TW Hya.”
• The Magnetic Fields of Classical T Tauri Stars (2007, background): “These come fromNeuhauser et al. (1995) except for DF Tau, DHTau, andGM Aur, which come from Damiani et al. (1995), and for TW Hya, which comes from Kastner et al. (2002).”
• CHEMICAL PROCESSES IN PROTOPLANETARY DISKS (2010, methodology): “Given the large X-ray luminosities of T Tauri stars (see e.g. Kastner et al. (1997, 2002)), we plan a more thorough study on the effects of X-ray desorption in protoplanetary disks taking into consideration the X-ray energy spectrum as a function of disk radius and height and investigating the full…”
• Young Stars Near the Sun (2004, background): “Accretion is perhaps also indicated from the 1.5–2.5 Å high resolution X-ray emission spectrum obtained with Chandra/HETGS by Kastner et al. (2002).”
• Highlights from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) (2006, background): “High electron densities up tone ≈ 1013 cm−3, measured in density-sensitive X-ray lines of CTTS, have indeed been attributed to shocked gas (Kastner et al. 2002) although the XEST sample is ambiguous in this respect, showing two accretors with low densities (AB Aur: Telleschi et al. 2007c; T Tau:…”
• EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, background): “Bright X-ray emission from T-Tauri stars is thought to arise from both the stellar corona as well as an accretion shock (Kastner et al. 2002; Brickhouse et al. 2010).”
• Imaging the Disk around TW Hydrae with the Submillimeter Array (2004, background): “…known classical T Tauri star, and exhibits high X-ray flux, large lithium abundance, and evidence for an actively accreting disk with accretion rate estimated to be from 10−9 to 10−8 M⊙ yr −1 based on the large Hα equivalent width and the X-ray emission (Kastner et al. 2002 and refs therein).”
• X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, methodology): “Kastner et al. (2002), Stelzer & Schmitt (2004), and Drake et al. (2005) found high Ne/Fe and Ne/O abundance ratios in the spectrum of TW Hya.”