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The finest features i n EUV solar images

The finest features i n EUV solar images. Jean-François Hochedez 1 Laurent Jacques 2 , Samuel Gissot 1 , Jean-Pierre Antoine 2 1 Royal Observatory of Belgium 2 Theoretical Physics Institute, UCL, Belgium. Longcope et al 2001. The smallest solar objects seen in EUV.

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The finest features i n EUV solar images

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  1. The finest featuresin EUV solar images Jean-François Hochedez 1 Laurent Jacques 2, Samuel Gissot 1 , Jean-Pierre Antoine 2 1 Royal Observatory of Belgium 2 Theoretical Physics Institute, UCL, Belgium

  2. Longcope et al 2001 The smallest solar objects seen in EUV • Bright Points Zhang et al ‘01 – EIT 195: • ~800 EUV BPs per Sun • Avg size 110 Mm2 ~33 EIT pxl • Avg lifetime 20 hours • T° < 2MK, intermittency and flaring • Relatively simple objects • Modeling • Priest et al 94, Longcope et al 98 • Cycle studies • Davis 77, Golub 79, Harvey 84, 93, Sattarov 02, Hara ‘03… • Tracers of Rotation • Brajsa 01, 02, Vrsnak 03 • Transient brightenings = micro-events(in QS, BP, AR, loops…) • « Nanoflare » scenario, Coronal heating • Krucker Benz 1998 (1M/hr), Berghmans et al 1998 (4000/hr) • Aschwanden 1999 • Sub-resolution reconnection • Meaningful sources of information on the heating process(es)

  3. Courtesy Berghmans (2002) Powerlaw index (a) Aschwanden et al, 2000b 2.5 Wtot = f ( E min, a) 2.0 1.5 18 20 22 24 1024 erg Energy release by smallest Event (log Emin) 1028 erg

  4. Nanoflare scenario falsified ? Powerlaw index (a) (Winebarger et al, 2002) Wtot > 1 x 107 erg/s cm2 (Krucker & Benz 1998) 2.5 (Parnell & Jupp 2000) Wtot > 3 x 105 erg/s cm2 2.0 (Aschwanden 2000) 1.5 Missing a factor ~30 in the QS 18 20 22 24 Courtesy Berghmans (2002) Energy release by smallest Event (log Emin)

  5. [Aschwanden, 1999] Flaring loops scaling laws and limits to their extrapolation L ~ Tne ~ T2=> p ~ T3 => Eth ~ T6 • p > pchromosphere => cut-off • Eth > 2.5 1023 erg • L > 5 Mm @ T= 1 MK From Berghmans 2002 L ~ T

  6. Outline • Observational issues • 2D-wavelet-based extraction method • Applications • Individual EIT & TRACE full-res images • 1-day EIT sequence at 195 (512x512) • Half a cycle of BPs in EIT 195 (1k2 rebinned to 2562)

  7. Bright Points, micro-events, … and Cosmic Ray Hits

  8. Observational issues Zhang et al 2001 • Cosmic ray hits (CRH) plague • Ambiguity (on the disc) between unresolved genuine solar PLS and CRH • Power law distribution of the AS brightness • Some extraction schemes rely on disc histogram treatments, but • Populations merge in the background « noise » or texture • Short lifetimes • Some extraction schemes rely on temporal treatments, but • Time series are undersampled • This work attempts to extract Point Like Structures/events (PLS) • With no assumption on disc brightness distribution • In individual images

  9. Continuous Wavelet Transform (CWT) of a Fe XV EIT image (1)

  10. 2-D CWT of a Fe XV EIT image (2)

  11. Mexican Hat (Maar 1976) Why the MH? • Isotropic = simple • MH and its Fourier transform are real computation speed • Explicit on gaussian peaks and ridges analytical modelling • Optimal detectivity for gaussian peaks on white noise • Almost optimal detectivity for gaussian peaks on 1/f noise • Vanishing moments : CWT(plane) (R) = 0,  R • L1 normalization

  12. Gaussian peakscan model BPs, Brightenings, CRH… Kappa/ = f(scale). pixels Wavelet coefficient as function of logarithmic scale at the peak

  13. Ridges can model Magnetic Loop Kappa/ = f(scale). pixels Wavelet coefficient as function of logarithmic scale on the ridge

  14. Wavelets applied on a Dirac The Lipschitz coefficient Wavelet coefficients of a pure Dirac Hölder/Lipschitz coefficient = Slope at smallest scales -2 for a Dirac Mallat 1992 « iw » Constructed numerically MH iw Scale in pixels

  15. Search for the smallest scalefor which Lipschitz = -2 (Dirac case) MH The « iw » wavelet allows, in principle, to access smaller scales than the MH. iw Scale in pixels

  16. If noise is added, the MH is more robust. Dirac + 30% gaussian noise MH With noise iw with noise iw without noise MH without noise

  17. Method applied on 1 image

  18. Histogram of Lipschitz coefficients of an EIT Fe XV image 2001 May 10., 19:20:52 Lipschitz < 0 = discontinuities -2 0 +2

  19. Peak value (above the background) Ad-hoc threshold 2-d Histogram Selected features Poisson photon noise Background value of the discontinuities 2001 May 10., 19:20:52

  20. 2001 May 10., 19:20:52

  21. EIT 304, level one (raw)

  22. EIT 304, discontinuities replaced by median

  23. EIT 284, level one (raw)

  24. EIT 284, discontinuities replaced by median

  25. TRACE 171 raw

  26. TRACE 171 discontinuities replaced by median

  27. Method applied on a 1-day EIT sequence19.5 nm, 512 x 512 whole May 15, 2001 106 images

  28. Movie • One day (15 May 2001) • 19,5 nm

  29. Cumulated extracted signal over 1 day 20010515

  30. 2 overlapping populations 1-day cumulated 2D histograms Peak value (above the background) 0 Lipschitz -1 Solar objects CRH (?) -2 Background value of the discontinuities Background value of the discontinuities

  31. There are solar PLS < 4 Mm & they live up to ~ 15 hr # of occurences 2001-05-15 Duration (Hours)

  32. Max brightness proportional to duration Maximum signal reached during the event lifetime Duration (Hours) 2001-05-15

  33. The 16 longest-lived events exhibit various behaviours

  34. Method applied on rebinned imagesto extract the BPs256 x 256 along the cycle in each EIT bandpass

  35. Extracting the BPs(instead of the micro-events & the CRH)by first rebinning to 256 x 256 1 pxl ~ 52 Mm2

  36. Half-cycle cumulated densities (smoothed) 171 195 284 304

  37. Number of BPs in 30-60 DN (CH intensities) as a function of time 19.5nm ÷ 20 1996 2002

  38. Area with 30-60 DN (CH) = f(t) 19.5nm ÷ 2.5 1996 2002

  39. Normalized number of BPs in the 30-60 DN as a function of time 19.5nm ÷ ~ 9 1996 2002

  40. Multi-temperature studies

  41. Conclusions • Method developped quantifies the strength of discontinuityfor small features. • 2 populations identifiedat Lipschitz = -1.8 and -0.4. • Some CRH are not pure dirac • Some true solar features could be dirac. • But a large fraction of PLS are of true solar origin. • Objects <16 Mm2 can live >10hr & exhibit micro-events.Contribution to coronal heating under study • From solar Min to solar Max, small BPs in CH at 195 seem to decrease in density by a factor ~ 9 • Davis et al 83 found 10, Hara Nakakubo’03 find no anticorrelation

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