Formation of Helium linesin solar prominencesNicolas LabrosseUniversity of Glasgow, Scotland, UK
Outline•Introduction on solar prominences•Radiative transfer modelling–Description of the models–Influence of the prominen...
Solar prominences                                                                                  prominence             ...
Puzzles•How do prominences form?–What is the magnetic configuration of filament channels, andhow is this highly sheared st...
Puzzles•Prominence fine structure and diagnostics–What are their detailed thermal and magnetic structures?–How can we use ...
Puzzles•Prominence disappearance–What can observations of heating and activation inprominences tell us about their disappe...
Physical parameters              Patsourakos & Vial (2002), Labrosse et al. (2010).2 November 2011   Presentation to Solar...
Plasma parametersTemperature, density, ionisation, filling factor, ...Accurate measurements are     crucial to construct r...
Non-LTE radiative transfer•Line formation–observations are difficult tounderstand•Necessity to solveequations–Statistical ...
H and He EUV resonance linesLyman lines of hydrogen form in different parts of theprominence (Heinzel 2007)Optically thick...
The prominence model                                      The prominence model•1D plane-parallel vertical slab       Anzer...
Prominence-corona transition region                                                              (PCTR)Temperature inside ...
He I model atomHe I: 29 energy levelsHe II: 4 energy levels76 bound-boundtransitions and 33 bound-free transitions561 tran...
Intensities and physical parametersHe I triplet line intensity ratio depends on prominence altitude                       ...
Influence of PCTR on line profiles                   H Lyman α                                             He I 584 Å     ...
Influence of PCTR on He I triplet lines•PCTR affects formation mechanisms of lines formedin cool parts of the prominence–s...
Prominence diagnostic with SUMER                  BBSO Hα                    MEDOC campaign #13,                          ...
Prominence diagnostic with SUMER●    Prominence model: 1D plane-parallel slab                                             ...
Prominence diagnostic with EIS                        np/nH                                                  n(HeII)/n(He)...
2D models   Ionisation degree in cylindrical prominence                                                                   ...
2D models                  Variation of the ionisation ratio with T                                                       ...
DiagnosticHe velocity fields                                                                    of I model atom●   Imaging...
Effects of radial motions                                                            Effects of radial motions•For a simpl...
V=0 km s-1                                        V=80 km s-1                                           T = 8000 K        ...
Plasma motions in prominences●   He II 304 Å line sensitive to Doppler dimming due to    radial motion of prominence plasm...
ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot   too denseCool   plasmaDoppler dimmin...
ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot too denseCool plasmaIncreasing column ...
ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot too denseCool plasmaIncreasing tempera...
Results (5)                                                                                          ResultsEffects on Hel...
E(He I 584) vs. radial velocity                  (erg s1 cm-2 sr-1 Å-1)                                           (PCTR = ...
E(He II 304) vs. radial velocity                  (erg s1 cm-2 sr-1 Å-1)                                           (PCTR =...
2011-06-10                                                                Labrosse & McGlinchey (subm)                  20...
Comparison with observations                                                               Labrosse & McGlinchey (subm)2 N...
Conclusions / Future plansImportance of taking into account PCTR–Affects plasma diagnostics from most lines in most casesC...
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Formation of Helium Lines in Prominences

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Presentation given to the Solar Physics group at Purple Mountain Observatory, Nanjing.

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Formation of Helium Lines in Prominences

  1. 1. Formation of Helium linesin solar prominencesNicolas LabrosseUniversity of Glasgow, Scotland, UK
  2. 2. Outline•Introduction on solar prominences•Radiative transfer modelling–Description of the models–Influence of the prominence-to-corona transition region(PCTR) on line profiles and intensities–Influence of the radial motions of the plasma on line profilesand intensities•Conclusions2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 2
  3. 3. Solar prominences prominence body T~8000 K n~1010 cm-3 corona T≥1-2 MK n~108 cm-3 SOHO/EIT2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 3
  4. 4. Puzzles•How do prominences form?–What is the magnetic configuration of filament channels, andhow is this highly sheared structure created?–Where does their dense material originate, and how is itmaintained?–How do prominences reach and maintain energy balance withthe ambient corona?–How are the magnetic structure and the plasma dynamicslinked? Labrosse et al. (2010), Mackay et al. (2010) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 4
  5. 5. Puzzles•Prominence fine structure and diagnostics–What are their detailed thermal and magnetic structures?–How can we use existing (SOHO, Hinode, STEREO, SDO)and future (Solar Orbiter) space missions to obtain the bestinformation on solar prominences?–Can we construct a prominence model that reproduces theobserved emission in optically thin and optically thick lines? Labrosse et al. (2010), Mackay et al. (2010) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 5
  6. 6. Puzzles•Prominence disappearance–What can observations of heating and activation inprominences tell us about their disappearance?–Why do filament channels generate the most energetic solareruptions?–What tools can we develop to forecast prominence eruptionsin a reliable way? Labrosse et al. (2010), Mackay et al. (2010) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 6
  7. 7. Physical parameters Patsourakos & Vial (2002), Labrosse et al. (2010).2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 7
  8. 8. Plasma parametersTemperature, density, ionisation, filling factor, ...Accurate measurements are crucial to construct realistic models of prominences difficult to obtain prominence plasma not in local thermodynamical equilibrium (non-LTE) because of strong incident radiation coming from the SunLarge span of measured values depending on the observed structure depending on the technique usedNon-LTE radiative transfer modelling of prominences sheds light on line formation mechanisms helps to interpret spectroscopic observations / imaging2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 8
  9. 9. Non-LTE radiative transfer•Line formation–observations are difficult tounderstand•Necessity to solveequations–Statistical equilibrium–Radiative transferincluding optically thick linesand continua•Non linear and nonlocal coupling betweenmatter and radiation 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 9
  10. 10. H and He EUV resonance linesLyman lines of hydrogen form in different parts of theprominence (Heinzel 2007)Optically thick core reveals fine structure close to prominenceboundariesOptically thin wings result from integration of several elementsalong LOSSame for He I and He II resonance linesHe I 584 Å, He I 537 Å, He II 304 Å, He II 256 ÅPlasma out of local thermodynamic equilibrium (LTE)Plasma diagnostics is complexNon-LTE radiative transfer calculations with velocity fieldsare needed to build realistic prominence models2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 10
  11. 11. The prominence model The prominence model•1D plane-parallel vertical slab Anzer & Heinzel (1999) Free parameters Gas pressure Temperature Column mass Height above the limb Radial velocity Equations to solve Pressure equilibrium, ionisation and statistical equilibria (SE), radiative transfer (RT) for H (20 levels) SE, RT for other elements: He I (29 levels) + He II (4 levels)
  12. 12. Prominence-corona transition region (PCTR)Temperature inside the prominence slab for γ=2 (extended PCTR), γ=10, andγ=20 (narrow PCTR). The column mass is M = 5×10−6 g cm−2 and the centraltemperature is 9000 K. 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 12
  13. 13. He I model atomHe I: 29 energy levelsHe II: 4 energy levels76 bound-boundtransitions and 33 bound-free transitions561 transitions overallWe can now calculate theemergent radiation.
  14. 14. Intensities and physical parametersHe I triplet line intensity ratio depends on prominence altitude E(10830)/E(D3) vs height above the limb Labrosse & Gouttebroze (2004) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 14
  15. 15. Influence of PCTR on line profiles H Lyman α He I 584 Å model without models with transition region transition region Labrosse et al (2002)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 15
  16. 16. Influence of PCTR on He I triplet lines•PCTR affects formation mechanisms of lines formedin cool parts of the prominence–statistical equilibrium of He I atomic states E(10830)/E(D3) vs optical depth at 504 Å T<6000 K T<6000 K T>16000 K T>16000 K Labrosse & Gouttebroze (2004) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 16
  17. 17. Prominence diagnostic with SUMER BBSO Hα MEDOC campaign #13, 15–16/6/2004 Observed profiles compared with grid of 4720 computed models (T, n, ...) ⇩Ly-β, Ly-ε, and He I 584 Å observed bySUMER/SOHO 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 17
  18. 18. Prominence diagnostic with SUMER● Prominence model: 1D plane-parallel slab Temperature profile inside prominence slab (Anzer & Heinzel 1999) ne = 6 108 cm-3 (surface) ne = 5 109 cm-3 (center) Labrosse, Vial, & Gouttebroze (2006) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 18
  19. 19. Prominence diagnostic with EIS np/nH n(HeII)/n(He) Surface: 1 Surface: 0.20 Centre: 0.94 Centre: 3.3x10-5 Max = 0.99 See also Heinzel et al. (2008), Labrosse et al. (2011) Temperature n(He III)/n(He) Surface: 105 K Surface: 0.8 Centre: 104 K Centre: 02 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 19
  20. 20. 2D models Ionisation degree in cylindrical prominence H + He ionisation H ionisation only Gouttebroze & Labrosse (2009)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 20
  21. 21. 2D models Variation of the ionisation ratio with T 30000-50000 K 20000 K 15000 K 10000 K 8000 K 6000 K Gouttebroze & Labrosse (2009)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 21
  22. 22. DiagnosticHe velocity fields of I model atom● Imaging measurements – apparent motion of structure in plane-of-sky● Doppler shifts in prominence spectra – velocity along line-of-sight● Doppler dimming / brightening – varies with radial velocity The full velocity vector may be inferred, but requires at least the radial velocity. 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 22
  23. 23. Effects of radial motions Effects of radial motions•For a simple 2-level atom with photo-excitation–Doppler dimming if the incident line is in emission–Doppler brightening if the incident line is in absorption•If coupling between several atomic levels–situation gets more complex: dimming and brightening–e.g. coupling between first two excited levels of H•Factors determining effects of radial motions–line formation mechanism–details of incident radiation (strength, emission/absorption)See Heinzel & Rompolt (1987), Gontikakis et al (1997), Labrosse et al (2007,2008) 2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 23
  24. 24. V=0 km s-1 V=80 km s-1 T = 8000 K T = 15000 K V=200 km s-1 V=400 km s-1He I 584 He II 304 He I 10830 Labrosse et al. (2007)
  25. 25. Plasma motions in prominences● He II 304 Å line sensitive to Doppler dimming due to radial motion of prominence plasma Labrosse et al. (2007)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 25
  26. 26. ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot too denseCool plasmaDoppler dimming of Lyman α line less pronouncedwhen PCTR is extended.increased contribution in line formation of collisional processes in higher temperature region relative to narrow PCTR case2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 26
  27. 27. ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot too denseCool plasmaIncreasing column mass with all other parameters keptconstant means more hot materialcollisionalcomponent of Ly-α becomes more important ⇒ the line is less sensitive to Doppler dimming2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 27
  28. 28. ResultsEffects on Lyman αDoppler dimming ifLarge temperature gradient in PCTRNot too denseCool plasmaIncreasing temperature of main prominence body increasesamount of hot materialcollisionalcomponent of Ly-α becomes more important ⇒ the line is less sensitive to Doppler dimming2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 28
  29. 29. Results (5) ResultsEffects on Heliumresonance lines(Same trend asLyman lines)Doppler dimmingCool plasmaNot too denseLarge temperature gradient in PCTREffects on Helium subordinate lines10830, D3, ... are less sensitive to Doppler dimming/brighteningdue to weak incident radiation2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 29
  30. 30. E(He I 584) vs. radial velocity (erg s1 cm-2 sr-1 Å-1) (PCTR = prominence-to-corona transition region)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 30
  31. 31. E(He II 304) vs. radial velocity (erg s1 cm-2 sr-1 Å-1) (PCTR = prominence-to-corona transition region)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 31
  32. 32. 2011-06-10 Labrosse & McGlinchey (subm) 2010-09-082 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 32
  33. 33. Comparison with observations Labrosse & McGlinchey (subm)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 33
  34. 34. Conclusions / Future plansImportance of taking into account PCTR–Affects plasma diagnostics from most lines in most casesCalculations provide constraints for determination of–Opacities–Ionisation degree – Variations in ionisation degree along LOS can be important–Radiative losses for energy balance calculationsCompare 2D calculations with observations–Models must be constrained by using several lines (H+He)2 November 2011 Presentation to Solar Physics Group at Purple Mountain Observatory 34

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