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H2012 ADAS Workshop Cadarache, France 24-25 Sept 2012

Diagnosing the Shock from Accretion onto a Young Star Nancy S. Brickhouse Harvard-Smithsonian Center for Astrophysics Collaborators: Steve Cranmer, Moritz Guenther Andrea Dupree, Juan Luna, and Scott Wolk. H2012 ADAS Workshop Cadarache, France 24-25 Sept 2012. Outline.

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H2012 ADAS Workshop Cadarache, France 24-25 Sept 2012

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  1. Diagnosing the Shock from Accretion onto a Young StarNancy S. BrickhouseHarvard-Smithsonian Center for AstrophysicsCollaborators: Steve Cranmer, Moritz GuentherAndrea Dupree, Juan Luna, and Scott Wolk H2012 ADAS Workshop Cadarache, France 24-25 Sept 2012

  2. Outline • Collisionally ionized plasmas and their X-ray spectra • Young stars: coronae and accretion • Case study: TW Hydrae (TW Hya) • Implications • Conclusions

  3. Collisionally Ionized Plasmas and Their X-ray Spectra • ATOMDB (Smith et al. 2001; Foster et al. 2012) • Collisionally ionized X-ray sources include: - Hot gas in galaxies - Hot gas in clusters of galaxies - Hot gas in the interstellar medium - Ejecta and shocks in supernova remnants - Shocks in hot star winds and binary colliding winds - Shocks from magnetically controlled accretion - Stellar coronae • 13 years of Chandra and XMM-Newton gratings for “point sources”

  4. Emission Measure (Ne2 V) of Stars (Kastner et al. 2002) log Ne2V (cm-3) log Te (K) Stellar coronae, but accretion shock in TW Hydrae? (Kastner et al. 2002)

  5. Other Young Stars

  6. Accretion or Corona? • Original argument for accretion shock based on high density • Additional diagnostics needed to test accretion-shock model ChandraLarge Observing Program TW Hya 500 ks with High Energy Transmission Grating (Brickhouse et al. 2010)

  7. TW Hya Campaign:Four Continents Plus Chandra Dupree et al. 2012

  8. TW Hya • Classical T Tauri star (accreting) • i=7o (pole-on) • M = 0.8 MSun • R = 0.7 RSun • Distance 57 pc • 10 million yr old • Poised to make planets Romanova et al. 2004

  9. Neon Region of HETG Spectrum Spectrum shows strong H-like Ne X and He-like Ne IX, up to n=7 or 8 in Ne X. Series lines are sensitive to absorption

  10. He-like Line Ratio Diagnostics He-like Energy Levels (Smith et al. 2009)

  11. Atomic Theory and Benchmarks:Ne IX G-ratio DiagnosticG-ratio vs Te Chen et al. 2006 Smith et al. 2009

  12. He-like Ions in TW Hya: O VII, Ne IX, and Mg XI Diagnostics for Te and Ne

  13. X-Ray Line Ratio Diagnostics for Density and Temperature Ne = 6 x 1012 cm-3 Mg XI 3 x 1012 Ne IX 6 x 1011 O VII Te = 2.50 ± 0.25 MK This looks like the accretion shock!

  14. Accretionand aCorona Emission Measure vs Te Light curve Hot “coronal” lines exhibit a large flare. The “accretion” lines do NOT flare. Variability occurs in both.

  15. Complex absorption Use photoelectric absorption model • O VII: NH = 4.1 x 1020 cm-2 • Ne IX: NH = 1.8 x 1021 cm-2 Not resonance scattering: Tau ~ g f λ, for a given ion Series line ratios rule out

  16. Accretion shock cools radiatively 2GM* R* Vff = (1 – R*/rt )1/2 ~ 510 km/s Te = 3.4 MK Macc = f A*ρpre vff ● (Konigl 1991; Cranmer 2008)

  17. Accretion shock cools radiatively 2GM* R* Vff = (1 – R*/rt )1/2 ~ 510 km/s Te = 3.4 MK Macc = f A*ρpre vff ● (Konigl 1991; Cranmer 2008) “Settling”

  18. The Splash:A New Accretion-Fed Post-Shock Structure Te and Ne from Ne IX agree with the shock model.Standard model predicts Ne at O VII 7 times larger than observed. Post-shock region has 30 x more mass than the shock!

  19. The Splash:A New Accretion-Fed Post-Shock Structure Te and Ne from Ne IX agree with the shock model.Standard model predicts Ne at O VII 7 times larger than observed. Post-shock region has 30 x more mass than the shock! Definitely not “settling”

  20. Soft X-ray Excess (OVII) Ubiquitous Gudel & Telleschi 2007

  21. Accretion Variation: Te, NH, Ne from Ne IX Te from 1.9 to 3.1 MK • 3 segments ~150 ksec each Te and NH differ. Ne varies only slightly. • Variable Te means rt changes. • Assuming NH is from pre-shock gas, we can get path length <l> and thus the filling factor. • Observed diagnostics constrain model Macc, B, f, rin and rout ● NH from 0.9 to 3.2 1021 cm-2 Brickhouse et al. 2012

  22. Accretion Model Variations Brickhouse et al. 2012

  23. Conclusions • Diagnostics show excellent agreement with simple models of the shock itself. • Diagnostics show that standard, one-dimensional models of the post-shock cooling plasma don’t explain all the data. • The shock heats and ionizes stellar material, potentially feeding open and closed field lines. • Without accurate diagnostics, studies such as this cannot take advantage of the potential of Chandra.

  24. Implications • How good is the dipole assumption? • How does the magnetic field evolve? • Do turbulent “hot spots” develop on more massive accretors? • What MHD processes drive stellar and/or disk outflows? • How does the magnetic field connect star and disk? Donati et al. 2008 BP Tau

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