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Solar Coronal Loop Workshop — Palermo 9/3/2004

Emission measure distribution in loops impulsively heated at the footpoints Paola Testa, Giovanni Peres, Fabio Reale Universita’ di Palermo. Solar Coronal Loop Workshop — Palermo 9/3/2004. GENERAL PROBLEMS OBSERVATIONAL EVIDENCE CORONAL LOOPS MODELS :

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Solar Coronal Loop Workshop — Palermo 9/3/2004

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  1. Emission measure distribution in loops impulsively heated at the footpointsPaola Testa, Giovanni Peres, Fabio RealeUniversita’ di Palermo Solar Coronal Loop Workshop — Palermo 9/3/2004

  2. GENERAL PROBLEMS • OBSERVATIONAL EVIDENCE • CORONAL LOOPS MODELS: • standard hydrostatic models vs. observations need for improved models • hydrodynamic model with footpoint heating Rationale Solar Coronal Loop Workshop — Palermo 9/3/2004

  3. GENERAL PROBLEMS:spatial and thermal structuring, heating, dynamic properties of solar and stellar coronae DIAGNOSTIC TOOLS: • SOLAR CORONA:high spatial and temporal resolution, spectral information • STELLAR CORONAE:X-ray spectral coverage with high spectral resolution Solar Coronal Loop Workshop — Palermo 9/3/2004

  4. Yohkoh/SXT TRACE 171Å Coronal LoopsLoops are basic components of the solar corona development of loop models: e.g. Rosner et al. 1978, Vesecky et al. 1979, Serio et al. 1981 Solar Coronal Loop Workshop — Palermo 9/3/2004

  5. Coronal LoopsLoops are basic components of the solar corona apparent disagreement mostly with EUV observations (TRACE, SoHO) : e.g. Aschwanden et al. 2000,2001, Winebarger et al. 2002, Warren et al. 2003 location of heating? : e.g. Priest et al. 2000, Aschwanden 2001, Reale 2002 Solar Coronal Loop Workshop — Palermo 9/3/2004

  6. Coronal LoopsLoops are basic components of the solar corona • how are active stars structured? • can simple loop modelsexplainthe emission from active stars? • solar analogy for interpreting stellar coronae? Solar Coronal Loop Workshop — Palermo 9/3/2004

  7. Lack of spatial resolution we must resort to indirect means for comparing properties of stellar coronal structures with solar loops spectral observations : high resolution EUV (EUVE) and X-ray spectra (Chandra, XMM-Newton) Emission Measure Distribution Coronal Loops in Stellar Coronae? EM(T)= Tne2(T) dV Solar Coronal Loop Workshop — Palermo 9/3/2004

  8. Scelsi et al. (2004) 31 Com e.g.EM(T) of 31Com from XMM spectra EM(T) expected for hydrostatic loop models T3/2 however Coronal Loops in Stellar Coronae? EM(T) derived from observations are steeper and with bumps, i.e. large amounts of almost isothermal plasma Solar Coronal Loop Workshop — Palermo 9/3/2004

  9. New Loop Models? • can footpoint heating yield loops with characteristics compatible with observations? Problem:INSTABILITY (e.g.Serio et al.1981) dynamic loops since static solutions do not exist for heating concentrated at the footpoints • how do EM(T) change with characteristics of heating? Solar Coronal Loop Workshop — Palermo 9/3/2004

  10. Loop Model • 1-D hydrodynamic loop model • symmetric equations solved for half loop • uniform cross-section • footpoint heated by periodic heat pulses • Palermo-Harvard code (Peres et al.,1982; Betta et al.,1997) consistently solves the time-dependent density, momentum and energy equations for the plasma confined by the magnetic field Solar Coronal Loop Workshop — Palermo 9/3/2004

  11. satisfy the scaling laws p0 ~ (Tmax/1.4·103 )3·1/L E0 ~ 105 p07/6·L-5/6 • INITIAL CONDITIONS: solutions of hydrostatic loop model(Serio et al. 1981) Loop Model • HEATING FUNCTION: • spatial distribution :  = L/3, L/5, L/10 EH (s,t) = EH (s)·EH (t) • temporal distribution : periodic pulses with duty cycle 10% EH (s) = H0·e-(s-s0)2/22 • intensity of heating scaled from the static model Solar Coronal Loop Workshop — Palermo 9/3/2004

  12. Initial Conditions Tmax p0 E0cool [MK] [dyn/cm2][erg cm-3s-1][s] 3 1 0.45 ~ 2200 10 36 30 ~ 1200 Set of simulations Solar Coronal Loop Workshop — Palermo 9/3/2004

  13. Heat Pulses  H  trun [s] L/3,L/5,L/10 E0,4E0 cool/4,cool /2 10000 L/3,L/5,L/10 E0,4E0 cool/4,cool /2 5000 Set of simulations Solar Coronal Loop Workshop — Palermo 9/3/2004

  14. Evolution of footpoint heated loopsConstant heating Solar Coronal Loop Workshop — Palermo 9/3/2004

  15. Evolution of footpoint heated loopsImpulsive heating Solar Coronal Loop Workshop — Palermo 9/3/2004

  16. Evolution of footpoint heated loopsTemperature and Density at loop apex Solar Coronal Loop Workshop — Palermo 9/3/2004

  17. Emission measure distribution Solar Coronal Loop Workshop — Palermo 9/3/2004

  18. Emission measure distribution:models vs. observations Solar Coronal Loop Workshop — Palermo 9/3/2004

  19. Conclusions Solar Coronal Loop Workshop — Palermo 9/3/2004

  20. Loop Model  effective plasma viscosity  fractional ionization ne/nH  hydrogen ionization potential • adaptive grid • initial model atmosphere usesVernazza, Avrett and Loeser (1980)toextend the S81 static model to chromospheric temperatures Solar Coronal Loop Workshop — Palermo 9/3/2004

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