1. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Testing Models of Coronal Heating, X-Ray Emission, and Winds... Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics... From Classical T Tauri Stars

2. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Testing Models of Coronal Heating, X-Ray Emission, and Winds... Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics... From Classical T Tauri Stars Outline: 1.Brief overview of T Tauri star & solar activity 2.Impact-driven turbulence: a plausible chain of events? 3.Testing the hypothesis: Accretion shocks Coronal loops Stellar winds

3. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 T Tauri stars: complex geometry & activity (Matt & Pudritz 2005, 2008) (Romanova et al. 2007) T Tauri stars show signatures of disk accretion, “magnetospheric accretion streams,” an X-ray corona, and polar (?) outflows from some combination of star & disk. Nearly every observational diagnostic varies in time, sometimes with stellar rotation, but often more irregularly. (Rucinski et al. 2008)

4. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Context from the Sun’s corona & wind Photospheric flux tubes are shaken by an observed spectrum of convective motions. Alfvén waves propagate along the field, and partly reflect back down (non-WKB). Nonlinear couplings allow MHD turbulence to occur: cascade produces dissipation. Open field lines see weaker turbulent heating & “wave pressure” acceleration Closed field lines experience strong turbulent heating

5. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Ansatz: accretion stream impacts make waves The impact of inhomogeneous “clumps” on the stellar surface can generate MHD waves that propagate out horizontally and enhance existing surface turbulence. Scheurwater & Kuijpers (1988) computed the fraction of a blob’s kinetic energy that is released in the form of far-field wave energy. Cranmer (2008, 2009) estimated wave power emitted by a steady stream of blobs. similar to solar flare generated Moreton/EUV waves?

6. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Testing the ansatz… with real stars Classical T Tauri stars in the Taurus-Auriga star forming region are well-observed: AA Tau BP Tau CY Tau DE Tau DF Tau DK Tau DN Tau DO Tau DS Tau GG Tau GI Tau GM Aur HN Tau UY Aur Cranmer (2009) used two independent sets of M *, L *, R *, ages, & accretion rates, from Hartigan et al. (1995) and Hartmann et al. (1998). Accretion spot “filling factors” δ taken from Calvet & Gullbring (1998) measurements of Balmer & Paschen continua → accretion energy fluxes & areas. Surface magnetic field strengths B * for 10/14 stars taken from Johns-Krull (2007) measurements of Ti-line Zeeman broadening; other 4 from empirical.

7. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Start with the simplest geometry Königl (1991) showed how inner-disk edge can scale with stellar parameters: Measured filling factor δ gives r outer, as well as size of blobs at stellar surface. Assume ballistic (free-fall) velocity to compute ram pressure; this gives ρ shock /ρ photo. The streams are inhomogeneous: Need to assume “contrast:” ρ blob / ≈ 3. This allows us to compute: L. Hartmann, lecture notes N (number of flux tubes impacting the star) Δt (inter-blob intermittency time)

8. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Accretion shock models Temporarily ignoring the existence of “blobs” allows a straightforward 1D calculation of time-steady shock conditions & the post-shock cooling zone. Typical post-shock conditions: log T e ~ 5–6, log n e ~ 13.5–15 Cranmer (2009) synthesized X-ray luminosities: ROSAT (PSPC), XMM (EPIC-pn).

9. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Results: accretion shock X-rays Blah…

10. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Coronal loops: MHD turbulent heating Cranmer (2009) modeled equatorial zones of T Tauri stars as a collection of closed loops, energized by “footpoint shaking” (via blob-impact surface turbulence). n = 0 (Kolmogorov), 3/2 (Gomez), 5/3 (Kraichnan), 2 (van Ballegooijen), f (V A /v eddy ) (Rappazzo) Coronal loops are always in motion, with waves & bulk flows propagating back and forth along the field lines. Traditional Kolmogorov (1941) dissipation must be modified because counter-propagating Alfvén waves aren’t simple “eddies.” T, ρ along loops computed via Martens (2010) scaling laws: log T max ~ 6.6–7.

11. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Results: coronal loop X-rays

12. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Stellar winds from polar regions The Scheurwater & Kuijpers (1988) wave generation mechanism allows us to compute the Alfvén wave velocity amplitude on the “polar cap” photosphere... Waves propagate up the flux tubes & accelerate the flow via “wave pressure.” If densities are low, waves cascade and dissipate, giving rise to T > 10 6 K. If densities are high, radiative cooling is too strong to allow coronal heating. Cranmer (2009) used the “cold” wave- driven wind theory of Holzer et al. (1983) to solve for stellar mass loss rates. v ┴ from accretion impacts photosph. sound speed v ┴ from interior convection 1 solar mass model )(

13. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 O I 6300 blueshifts (yellow) (Hartigan et al. 1995) Model predictions Results: wind mass loss rates O I 6300 blueshifts (yellow) (Hartigan et al. 1995) Model predictions

14. Testing Models of CTTS Coronal Heating, X-Ray Emission, & WindsS. R. Cranmer, July 14, 2010 Conclusions For more information: http://www.cfa.harvard.edu/~scranmer/ Insights from solar MHD have led to models that demonstrate how the accretion energy can contribute significantly to driving T Tauri outflows & X-ray emission. Brown et al. (2010) Is M wind enough to solve the T Tauri angular momentum problem? Why do (non-accreting) weak-lined T Tauri stars show stronger X-rays?. More realistic models must include: (1) more complex magnetic fields, and (2) the effects of rapid rotation on convective dynamo “activity.” Cohen et al. (2010)