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Structure of solar coronal loops:
from miniature to large-scale Hardi Peter
Max Planck Institute
for Solar System Research
Germany
peter@mps.mpg.de
S. Bingert,
J. A. Klimchuk, C. de Forest,
J. W. Cirtain, L. Golub,
A. R. Winebarger,
K. Kobayashi, K. E. Korreck
– miniature loops
– sub-structure of loops
A&A in press / arXiv 1306.4685
Corona and chromosphere in Hi-C FOV
→ very complex active region: group with may spots
→ no “normal” nice large active region loops…
Small coronal structures
► Hi-C sees structures down to resolution limit
► are these “miniature coronal loops” ? 100x shorter than “normal” loops
→ length: 1.5”– 2” → width: 0.3”– 0.4”
0.2” x 0.2” →Hi-C resolution:
SDO context
Nature of the small coronal structures
– footpoints of hot loops ?probably not: where is the hot loop?!
– really small loops ?HMI shows “monopolar” region…but opposite polarities might be hidden…
15” x 15”
Magnetic field on small scales: the photosphere
–1000
vert
ical m
ag
neti
c fi
eld
[G
]
+1000
0
–400
+400
0
l.o.s
mag
neti
c fi
eld
[G
]HMI / SDO (0.5”/pxl) IMaX/SUNRISE (0.05”/pxl)40” x 40”
Wiegelmann et al (2010) ApJ 723, L185
comparison of HMI and IMaX, not showing the same structures…
≈0.6”
SUNRISE data:opposite polaritieswith footpoint distance ≈ 1”within “unipolar” regions
4.5” x 4.5”
15” x 15”
15” x 15”
miniature loop
Miniature coronal loops ?!
^
^
corona
chromosphere& photosphere
interior
~ 2 Mm
~ 2 Mm
≈ 2”
► there is observational evidence small magnetic loops that reach “into corona”
e.g. Ishikawa et al (2010) ApJ 713, 1310
► can such loops exist ?!
Corona and chromosphere in Hi-C FOV
→ very complex active region: group with may spots
→ no “normal” nice large active region loops…
Comparison of Hi-C and AIA→ clear difference in plage region (upper left)
→ similar appearance in loop region
Hi-C193 Å
Comparison of Hi-C and AIA→ clear difference in plage region (upper left)
→ similar appearance in loop region
AIA193 Å
No sub-structure of loops
► Hi-C has more noise (higher resolution / less photons)
► no substructure visible in loops ! (within noise level)
0.2” x 0.2” →Hi-C resolution:
Getting a lower limit for the strand diameter
diameter ofindividual strands
number of strandsin whole loop:
Either strands have to be smaller than 15 km or the loop is monolithic !
Visualization of strands and cross-loop profile
Hi-C
AIA
integrate along Y – apply PSF – bin to AIA/Hi-C pixel size
Morphological comparison to modelobservations show:
(a) constant cross-section loops in expanding envelope
(b) thin individual loops
(c) thick non-expanding structures
3D MHD modelsshow similar features
→ more work is needed for quantitative comparison…
See also talk by Feng Chenon Wed morning:
“A coupled model for the formation of active region corona”
Conclusions
Structure of solar coronal loops:
from miniature to large-scale
► tiny coronal loop-like structures exist (loop length below 2 Mm)
→ are these miniature coronal loops?
→ how are they connected to the photosphere ?
→ how are they sustained ?
► long coronal loops appear to have no substructure in Hi-C observations (0.2” spatial resolution)
→ either smooth structures
→ or very thin strands (much smaller that 100 km)
High-resolution Coronal Imager (Hi-C)
– single rocket flight on 11 Jul 2012 (NASA/MSFC/CfA/LMSAL)
– imaging in 193 Å band identical to AIA/SDO
– 6x higher resolution compared to AIA
– 5 minutes of data from one active region– first results and description: Cirtain et al (2013) Nat. 493, 501
Hi-C AIA/SDO
pixel size 0.1” 0.6”
FOV ~400” full disk
channel 193 Å 193 Å and many more [ Fe XII ~1.5 MK ]
time cadence 5.5 s 12 sobs. time: 5 min … years
SDO context
Nature of the smallest coronal structures– footpoints of hot loops ?
probably not: where is the hot loop?!
– really small loops ?HMI shows “monopolar” region…but opposite polarities might be hidden…
15” x 15”
45” x 45”
^
Observation of small “photospheric loops
4” x 2.3”
circularpolarization
linearpolarization
integratedlight
time → Dt = 0 s 130 s 260 sHinode/SOTIshikawa et al (2010) ApJ 713, 1310
emergingfluxin / arounda granule
1- signal in lin. pol.
2- circ. pol. at sides
3- lin.pol. vanishes
^
corona
photosphere
interior
consistentwithflux tubebreakingthroughphotosphere
^
Observation of small “photospheric loops
4” x 2.3”
circularpolarization
linearpolarization
integratedlight
time → Dt = 0 s 130 s 260 sHinode/SOTIshikawa et al (2010) ApJ 713, 1310
emergingfluxin / arounda granule
1- signal in lin. pol.
2- circ. pol. at sides
3- lin.pol. vanishes
^
Ish
ika
wa
et a
l (20
10)
reconstruction of B at Dt = 130 s: is this a “photospheric loop” ?
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