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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

AIA 193 Å image during Hi-C flight

Hi-C FOV

Cirt

ain

et

al.

(201

3)

Nat

. 49

3, 5

01

Corona and chromosphere in Hi-C FOV

→ very complex active region: group with may spots

→ no “normal” nice large active region loops…

miniaturecoronal 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 ?!

sub-structure of

coronal loops

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

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” ?

Size of structures across the loop

Der

e et

al.

(198

7) S

olar

Phy

s. 1

14,

223

corduroy trousers scenario

Multi-stranded loops ?classical multi-stranded loop scenario

r ~200 km

D

r ≲ D → few strands

hp 2

013

©

r < D → very many strands<

veryfine

strands

Hi-C pixel size

~2 Mm