Ph.D. Dissertation Defense
NEW FACET OF SOLAR ACTIVITIES
REVEALED BY HIGH-RESOLUTION
IMAGING AT HE I 10830 Å
Zhicheng Zeng
New Jersey Institute of Technology
Advisor: Wenda Cao
Co-advisor: Vasyl Yurchyshyn
Journal Publications
 Z. Zeng, B. Chen, H. Ji, P. R. Goode, and W. Cao, “Resolving the Fan-Spine
Reconnection Geometry of a Small-Scale Chromospheric Jet Event with the New Solar
Telescope,” The Astrophysical Journal Letter, vol. 819, pp. L3, 2016.
 Z. Zeng, J. Qiu, W. Cao and P. G. Judge, “A Flare Observed in Coronal, Transition Region,
and Helium I 10830 Å Emissions,” The Astrophysical Journal, vol. 793, pp. 87, 2014.
 Z. Zeng, W. Cao and H. Ji, “Observation of Magnetic Reconnection Driven by Granular
Scale Advection,” The Astrophysical Journal Letter, vol. 769, pp. L33, 2013.
 H. Wang, W. Cao, C. Liu, Y Xu, R. Liu, Z. Zeng, J. Chae, and Haisheng Ji “Witnessing
Magnetic Twist with High-Resolution Observations from the 1.6 m New Solar
Telescope,” Nature Communication, vol. 6, pp. 7008, 2015.
 H. Wang and C. Liu, N. Deng, Z. Zeng, Y. Xu, J. Jing, and W. Cao, “Study of Two
Successive Three-ribbon Solar Flares on 2012 July 6,” The Astrophysical Journal Letter,
vol. 781, pp. L23, 2014.
Presentations
 Z. Zeng, J. Qiu, W. Cao and P. G. Judge, “A Flare Observed in
Coronal, Transition Region, and Helium I 10830 Å Emissions,”
AAS/Solar Physics Division Meeting, Boston, Massachusetts,
June 2-5, 2014.
 Z. Zeng, W. Cao and H. Ji, “Observation of Magnetic
Reconnection Driven by Granular Scale Advection,” AAS/Solar
Physics Division Meeting, Bozeman, Montana, June 7-12, 2013.
Contents
1. Motivation
2. Researches and significant result
3. Summary and Future Work
Introduction
NEW FACET OF SOLAR ACTIVITIES REVEALED
BY HIGH-RESOLUTION IMAGING AT HE I
10830 Å
 Solar Activity
 High Resolution Observation with NST
 Helium I 10830 Å Lines
Solar activity
X-class flare in Jul. 14 2000
Trace
Impact on
our life
 Communication
 GPS
 Space missions
 Spacecraft drag
 Induced current
Small-scale Solar Activity
Small Surges/Jets
 Microflares
 Ellerman bombs
 Type II spicules
 Small filament eruptions
Why small-scale activity
 Epitome of large-scale solar activity
similar physical mechanism
clearer physical picture
 Easy to be pinned down to the photosphere
 Precede the large-scale activity
(responsible for energy build-up)
 Large number of samples to study
Our star is a sea of small activities
Power law
spectrum
There are much
more activities with
smaller magnitude
Courtesy Li, Gan, & Feng
NST Features
 All reflecting, off-axis Gregory optical
configuration
 PM: 1.6 m clear aperture with f/2.4
 Figuring PM to 16 nm rms
 Effective focal length: 83.2 m (F/52 at
Gregorian focus)
 FOV: 2' in prime focus
 Wavelength range from 380 nm to
1.7 µm in Coudé lab with AO
 PM active thermally controlled
 Adaptive optics (AO)
 Quasi-static telescope alignment
 Diffraction limited: 0.06″@ 500 nm
and 0.2″@ 1.56 m with AO
 WFS, polarization and calibration
optics immediately before M3
 Facility-class instruments
High Resolution Photometry with NST
Helium I 10830 Å lines
Parahelium


Orthohelium
He I triplet: 10829.091, 10830.250, 10830.340 Å (geff = 2.0, 1.75 and 1.25,
respectively), arising as a transition between the 23P0,1,2 and the 23S1 of He I
Excitation mechanism:
 Ionization (coronal UV and X-ray, collisional) followed by a cascade to 23S1
 Collisional excitation (>20000 K) from the ground level 11S0 parahelium state
sensitive to dynamic phenomena, optically thin
Solar atmosphere
Courtesy Wedemeyer-Bhm et al., 2009
Chromospheric Obs. with Ha 6563 Å
and He I 10830 Å Lines
Photoionization Recombination
vs. Collisional excitation
• Strong self-absorption in
the core of parahelium
resonance lines
• line strength reduction not
comparable with coronal
radiation suppression
• Boundaries sharp (not
diffused)
• For collisional
Excitation of He : so
much high T
material is needed
that a high thermal
radio emission at
centimeter would
be observed (not
real)
Correspondence to EUV
SOHO/EIT
He I lines are weakened in coronal
holes
Contents
1. Introduction
2. Sources of Data, Analyzing Tools, and Models
3. Surge Triggered by Advection of A Large Granule
4. Probing the Formation of He I by studying A Flare Observed in
Coronal, Transition Region, and He I 10830 Å Emission
5. Resolving the Fan-spine reconnection Geometry of a Small-scale
Chromospheric Jet Event with the NST
6. Summary and Future Work
Data Sources
Instrument
NST/BBSO
(Ground based)
Species
Cadence
Resolution
FOV/LC
TiO
10 sec
0.034"/pix
70"
H𝛼
10 sec
(spectroscopy)
0.048"/pix
50"
He I 10830 Å
10 sec
0.083"/pix
85"
Magnetrogram
45 sec (los)
1"
Full disk
White-light C
45 sec
1’’
Full disk
(E)UV
12/24 sec
0.6"/pix
Full disk
HMI /SDO
AIA / SDO
RHESSI
XRT/Hinode
GBM/Femi
GOES
New Solar Telescope (NST); Big Bear Solar Observatory (BBSO);
Helioseismic and Magnetic Imager (HMI);
Atmospheric Imaging Assembly (AIA); Solar Dynamics Observatory (SDO)
Speckle reconstruction
Kiepenheuer-Institute Speckle Interferometry Package (KISIP)
(Wöger, F. & von der Lühe, O. 2008)

C programming language (core)

Enhanced for parallel processing
Fourier local correlation tracking (FLCT)
Code (Fisher et al. 2008 )
 Written in C, using the
FFTW3 library (“Fastest
Fourier Transform in the
West”)
 Designed for easy usage
within an IDL or GDL
session
 Latest version (1.01)
(4096 by 4096 images in
about 6 minutes)
EBTEL Model
• 0D Enthalpy Based Thermal Evolution Of Loops Model
describes average temperature, density and pressure across a
coronal strand (Klimchuk et al. 2008 and Cargil et al. 2012)
 dn i
dPi 2 
1
c2
 Qi  Rc  Rtr i ,

(F0 )  Rtr i

 dt 5c 3 kLiTi
dt 3 
Li
(i  1,2,3,....1000...)
Qi , Li : measured/inferred from observations
F0 : thermal conduction flux, function of Ti and n i
Rc : corona radiation rate, function of Ti and n i
Rtr : energy loss rate from the base;
OUTLINE
 Surge Triggered by Advection of A Large
Granule
 Probing the Formation of He I by studying A
Flare Observed in Coronal, Transition
Region, and He I 10830 Å Emission
 Resolving the Fan-spine reconnection
Geometry of a Small-scale Chromospheric
Jet Event with the NST
Small surge on Jul 22 2011
 Full disk AIA 171 Å
 Sub-region full-disk
Ha filtergram
 He I 10830 Å
filtergram
 Contours (171 Å
emission)
Alignments
TiO over He I 10830
Alignment between HMI and TiO
Composite image
 Back ground: TiO image.
 Pink: absorption
features extracted from
10830 Å filtergram.
 Red and blue contours:
positive and negative
magnetic field from HMI
LOS magnetogram)
Time sequence images
 Series of He I
10830 Å
filtergrams
 TiO images (gray)
overlaid with the
surge (pink)
Emergence
Cancellation
 Time series of
contours of LOS
magnetic field
Squeezed
Time profiles of the surge
 a: 10830 Å
 b: positive magnetic flux
Steep
increase
 C: negative magnetic flux
 d: EUV emission
171 Å (dotted line) Cancellation
94 Å (solid line)
Slightly
decrease
Summary
Flux emergence
Granular advection
Magnetic reconnection
Surge
Evidence of finest-scale reconnection process driven by the
large granule’s motion!
OUTLINE
 Surge Triggered by Advection of A Large
Granule
 Probing the Formation of He I by studying A
Flare Observed in Coronal, Transition
Region, and He I 10830 Å Emission
 Resolving the Fan-spine reconnection
Geometry of a Small-scale Chromospheric
Jet Event with the NST
Motivation:
To probe the mechanisms lead to the
strong He I 10830 A emissions
Total optically-thin energy flux
during decay phase
EBTEL model
Photoionization
and
Recombination
10830 observation
Compare
Total optically-thin energy flux
below 504 A
Our observation: C3.9 Flare, Jun 17th
2012
Blue: 193 A
Red: 10830
10830 A fitergram
Ebtel model

Light curves for all footpoint pixels
in different wavelengths : He I
10830, 1600, and He II 304.

Rapid rise and slow decay
All rising rapidly:
about 1 min.
Slow decay:

AIA 1600 decay
quickly;

He II 304 decay
slower;

He I 10830
decay much
slower.
EBTEL Model
Rapid rise
Energy input
Conduction flux
Long
decay
 plasma density: n
 plasma
temperature: T.
Uniform P
B
Static
equilibrium
Radiation flux
The transition region differential emission measure (DEM)
(Fisher et al. 1987):

 T 1

2
DEM(T)  g(T)P, with g(T) 
2 T  T T' (T')dT' 
8kB
 0

0
1
2
1
2
Comparing the results to observation
Radiation   C (T ) ndV n   C (T ) DEM (T )dT  P  C (T ) g (T )dT
𝐶(T) : response function, related to ndV : more particles n: collision excitation related
to density of plasma
like Saha equation, line emission
more radiation
Using 1600 signal of
each pixel to infer
Heating rate (dashed)
Input
Solid: Observation
Dotted: Synthetic
flux calculated
through EBTEL.
Good DEM
Approximation!
1. Use EBTEL model to obtain the DEM, then we
could calculate the corona emission
R  P   (T ) g (T )dT
𝛬(𝑇): 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝑙𝑜𝑠𝑠 𝑓𝑢𝑛𝑐𝑡𝑖𝑜𝑛
2. Use specific model of 10830 A emission to
estimate the corona emission and compare.
Total optically-thin energy flux
during decay phase
EBTEL model
Photoionization
and
Recombination
10830 observation
Compare
Total optically-thin energy flux
below 504 A
Inferring the emission from 10830 A
observation
Light curve
Continuum
(assumed)
1.
2. Absorption is
small (quiescent)
How many times
the continuum
How much flux
generated
Number of 10830
photons generated
Number of photons
emitted per
ionization
Total number of ionizing
photons needed
Minimum flux of ionizing
photons below 504
angstrom needed erg/cm2/s
Comparing the mission for different
patches
Red: calculated
from model.
Black: inferred
form 10830
observation.
Conclusions
1. Morphology of the footpoint 10830 Å emission is
qualitatively similar to a mixture of EUV channels.
2. Light curve of 10830 Å emission is, during the rise phase,
similar to the (E)UV transition region light curves (304 Å
and 1600 Å channel); during the decaying phases, it is
more similar to the coronal SXR and EUV light curves.
3. The EUV radiation computed from the EBTEL models is
compatible with the photon budget for exciting 10830 Å
via PR, during the decay phase.
• Photo-ionization followed by recombination (PR)
appears to be a prominent component exciting the
10830 Å multiplet during this event !
OUTLINE

Surge Triggered by Advection of A Large Granule

Probing the Formation of He I by studying A Flare
Observed in Coronal, Transition Region, and He I
10830 Å Emission
 Resolving the Fan-spine reconnection Geometry of
a Small-scale Chromospheric Jet Event with the
NST
More comprehensive picture of
chromospheric Jet
July 8,2012
 Direct observations of fan-spine structures is rare
for chromospheric jets:
1. Inverted-Y-shaped feature
2. Dome-shaped jet’s base outlined by coronalrain-like flows.
The Jet event on July 8,2012
Footpoint of
a closed
coronal loop
system
AR 11515:
18:19-18:50 UT
AIA 171
Countour
10’’ wide,
penumbral
region
AIA 304
18:18:50 UT
18:38:40 UT
Step I
Step I
Resolved
loops
Transverse
motion
Step I
Bi-directional
flow: ~30 km/s
X symbol
Stilt 1
Step II
Step II
RHESSI 6-12
KeV
Transverse
motion to
the left
Dark spine
(white arrows)
Step II
Bi-directional
flow:20 km/s
X symbol
Stilt 2
Summary
• First, the root of the inner spine coincides with
localized Hα, EUV, and X-ray emissions.
Intense heating
Magnetic
reconnection
• Second, bi-directional plasma flows are
observed at the onset of each step.
Near apex of the fan
~1800 km above footpoint
flow speed ∼20-30 km s
Magnetic null
point
Reconnection out
flow/ pressuredriven flow
Consistent with the two-step magnetic reconnection scenario of
jets proposed by Torok et al. (2009)
Mixture of heated
and cooled loops
Reconnected
loops
Cool plasma
Slingshot
Ambient,
unipolar
Heated
upward
field
ejection
Emerged negative
Reconnected
magnetic flux
loops
Accelerated
particles/thermal
conduction
Conclusions
The evolution of the jet is consistent with a two-step
reconnection scenario
• Fan ≤20000 K (absent in EUV and XRT but He I)
• In the fan, collisional mechanism is favored (insufficient EUV
emission)
• Reconnection site embedded in cool chromosphere (outer spine:
reconnected energy heated and sling-shot cool plasma)
• Inner spine is dark in 10830 ˚A, Hα, and EUV (>10 MK X-ray source at the
footpoint ) (a cool filament-like structure?)
Summary and Future Work
 Surges could be triggered by motions of large granules
• Large granule with velocity ~ 2 km 𝑠 −1
• Magnetic cancellation
 The chromospheric jet event is generated through two-step magnetic
reconnection.
• Resolved fan-spine geometry
• Bi-directional flow originated from null point
 At the flare footpoint, PR is of great importance for populating the
10830 Å multiplet during the cooling phase
Future Work
• Statistical study of surges and underneath
photospheric motions
• Learn some models for 10830 radiation
calculation
• NIR Imaging Spectro-polarimeter
Acknowledgement
• Advisors: Wenda Cao
• Co-advisor: Vasyl Yurchyshyn
• Committee members: Haisheng Ji, Philip R. Goode, Andrei
Sirenko, and Zhen Wu
• CSTR/SWRL/BBSO staff and students (specially Haimin Wang,
Dr. Bin chen, Dr. Chang Liu, Ju Jing, Dr. Yan Xu, Dr. Na Deng, Dr.
Gregory Fleishman, Dr. Shuo Wang, Ms. Christine Oertel, and
Ms. Cheryl James, Xin Chen, Xu Yang)
• Dr. Jiong Qiu at Montana University, Dr. Philip Judge at NSO
• Financial support from:
National Science Foundation and NASA under Grants AGS0847126, AGS-1146896 NSFC-11333009, NSFC-11428309, and
AFOSR (FA 9550-15-1-0322).