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Solar Cycle 24, Napa, December 2008

Active Region Loops - Observational Constraints on Heating from Hinode/EIS Observations Helen E. Mason DAMTP, Centre for Mathematical Sciences, University of Cambridge Cristina Chifor, DAMTP, Giulio Del Zanna, DAMTP, Brendan O’Dwyer, DAMTP, Durgesh Tripathi, DAMTP, Peter Young, NRL.

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Solar Cycle 24, Napa, December 2008

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  1. Active Region Loops - Observational Constraints on Heating fromHinode/EISObservationsHelen E. MasonDAMTP, Centre for Mathematical Sciences,University of CambridgeCristina Chifor, DAMTP, Giulio Del Zanna, DAMTP, Brendan O’Dwyer, DAMTP, Durgesh Tripathi, DAMTP, Peter Young, NRL Photo: Giulio Del Zanna Solar Cycle 24, Napa, December 2008

  2. Active Region loops: Open questions • Are quiescent (1MK) loops isothermal or multi-thermal along the line of sight? • Is there a weak high temperature component for all AR loops? • Loop structures appear fuzzier at higher temperatures: is this real or just the matter of spatial resolution? • What are the values of densities and the filling factors of a coronal loop? How do they vary along the loop length? • How does the temperature vary along the loop length? • What are the plasma flow in the active region loops? • What are the physical properties of the ‘moss’? • Do the hot, dense core loops interact with the larger, cooler 1MK loops?

  3. Hinode/EIS: Intensity, velocity and line width maps Young, 2007 Doschek et al, 2008 Intensity • Active region map • Fe XII 195.12 Å • Dec 2, 2006 For the first time, using Hinode/EIS, we are able to derived detailed maps of electron density, temperature, flows, non-thermal broadenings, and fill factors. However, rastering can be slow, so carefully designed EIS sequences are needed to obtain observations with a good cadence. Velocity Width

  4. Flow patterns are different at different temperatures and persist for several days. Active region flows at different temperaturesDel Zanna, 2007, 2008 HEALTH WARNING! Several of the EIS spectral lines are blended – dealing with the blends is difficult. There are several papers, eg led by Young, Del Zanna and others to aid identifications. Resolving idividual lines, especially weak ones is tricky. Deriving velocity shifts is even more ‘tricky’!! Seek advice from the EIS team.

  5. EIS observations: May 19, 2007, Tripathi et al, 2008 1 arcsec slit Exp time=40s Obs seq: “AR_velocity_maps” 8.0 – 10.5 7.0 – 12.0 8.0 – 9.8 8.0 – 10.5 8.5 – 11.0 11:41:23 16:35:01

  6. Flows in individual structures Tripathi et al, 2008 • With EIS, we can measure flows with a precision of ±3 km/s in spatially resolved coronal structures. • We can measure flows simultaneously • at different temperatures from: • log T = 5.6 MK (Fe VIII) to log T = 6.4 (Fe XV). • Velocity flows are seen along the AR loops, predominantly red-shifted at cool temperatures (see Si VII, left). • Blue-shifted flows are seen in other parts of the AR particularly at higher temperatures.

  7. Flows near loop footpoints at different temperatures The foot point regions show red-shifted emission at lower temperatures. However, blue shifts dominate at high temperatures.

  8. log T = 5.8 log T = 6.0 log T = 6.1 log T = 6.2 log T = 6.3 log T = 6.4 Intensity variation across loop structures Intensity cut across a loop (between the two white lines). At low temperatures the loops are sharp, at higher temperatures they become diffuse.

  9. Iobs = Background removed observed intensities A(b) = Abundances (Coronal Abundance) G (Ne, Te) = Contribution function EM [Te ]= Iobs /[A (b) G(Ne,Te)] Temperature along the loop: EM-Loci Temperature rises from 0.8MK at base to 1.5MK at the loop top. Mildly multi-thermal?

  10. Electron density along loop A Electron number densities along a loop Fe XII Log Ne (cm -3) Mg VII Si X Height (Mm) BG Background Electron densities are 1010 cm-3 at the base of the loop and fall to 108.5 cm-3 higher up (Background has been subtracted). MgVII densities seem lower that FeXII and SiX.We obtained a low value of filling factor (0.02 – 0.05) at log T = 6.1 MK and a filling factor close to 1 at log T = 5.8 MK towards the foot point of the loop.

  11. Active Region Observation – focus on ‘core’Tripathi et al, 2008 MAY 01, 2007 LOOPS SUNSPOT MOSS EIS FOV

  12. EIS sequence (cam_artb_cds_a) Raster using 2 arcsec slit Total time 20 minutes Exposure time 10 sec FOV 200 X 200 arcsec Active Regions Observations – focus on core EIS Fe XII 195

  13. Active region Moss at different temperatures The TRACE emission is similar to EIS SiVIII and the XRT to EIS FeXV

  14. Density map derived from Fe XII (186.88+186.85/195.12+195.17) The density in the core of the active region can be as high as 1010.5 cm-3 The density is highest at a temperature of Log T = 6.1

  15. EIS: Comparison of density map with magnetic field Note that the high densities are in +ve polarity regions not the sunspot side. The density correlates well with the strength of the +ve magnetic field.

  16. Limb Active Region - EIS ObservationsO’Dwyer, Mason, Del Zanna, Tripathi and Young, 2009, unpublished Dec 17, 2007 Target of Opportunity AR close to the limb, but with core still on disk Hinode Joint Observing Sequence - + Alphonse Stirling CAM_AR_LIMB_v1 2" slit 45sec exposure full length slit 6' wide raster run time: 2.5 hours

  17. Intensity variation for some EIS lines These observations can be used to determine line blends, average temperature and density along the line of site, across and above the AR .

  18. Average density along the line of sight The electron density measured from the FeXII 203/202 diagnostic ratio. The average density peaks in the core of the AR.

  19. Average electron density map from FeXIII lines Average temperature and density maps for the AR Temperature map from FeXVI/FeXV Red is Log T = 6.7, yellow is Log T= 6.5 Hot, dense AR cores are clearly seen with EIS. XRT shows ‘dynamic’ activity. These data confirm earlier results with CDS (Mason et al, 1999), but are much better.

  20. At T around 1MK, red-shifts in loops are ubiquitous. • Blue-shifts are present in higher temperature emission. • Smoking gun! Multi-strands – heating, evaporating and condensing? • Non-thermal broadening associated with blue-shifts. • Density in 1MK loop is 1010 cm-3 at the base and falls to 108.5 cm-3 higher up. • Temperature in the loop rises from 0.7MK at base to 1.5MK higher up. • Could be mildly ‘multi-thermal? Jury is still out! High temperature emission • is predicted by nano-flare models (eg EBTEL). It is very difficult to analyse • EIS high temperature lines (because of line blending). • EIS density and temperature maps show great detail (much better than CDS). • The temperature in the hot, dense core exceeds log T = 6.7, and the • density exceeds 1010 cm-3 . • The ‘moss’ regions have a high densities as high as 1010.5 cm-3 at Log T of 6.1. • The density is correlated with the magnetic field (on the non-sunspot side) Summary and Conclusions

  21. Flux emergence and braiding could cause reconnection at the boundaries as the active region grows. This could cause a turbulent regime with evaporation strongest at higher temperatures. Cool loops are mainly radiatively cooling, so we see predominant red-shifts (downward flowing plasma). Definitely need multi-strand models. What about the hot dynamic cores? Could the flux be submerging again in the core? Are we in equilibrium?! Recent (independent) work by Bradshaw and Serio discuss the need for time dependent ionisation calculations. Need good atomic data - CHIANTI v6 – to be released soon, includes ionisation and recombination rates. Next few years should be really exciting. So far we’ve just had a taster of AR observations!! Possible Scenario? Zwaan 1985

  22. EIS has already provided some fascinating and new observations of active regions. This talk has outlined work led by Cambridge. Active regions are very dynamic. Work by other members of the EIS team, eg Harry Warren, Ignatio Ugarte-Urra, Dochek et al studying dynamic activity was discussed yesterday. EIS sequences are being devised to optimise the diagnostics and to track the dynamics of active region structures – this balance is perhaps the most difficult to achieve. A carefully designed combination of different EIS and Hinode -wide observing modes is needed. So far, we have just had a ‘taster’, hopefully there will be a lot more EIS data to analyse once solar cycle 24 gets going.. IT’S A VERY EXCITING TIME...!! The Future?

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