Basic requirements to the instrument for
diagnostics of chromospheric magnetic ﬁelds
with SOLAR-C
Y. Katsukawa (NAOJ)
SOLAR-C subWG for chromosphere/corona magnetic field measurments Key concepts of the optical telescope•! The 1.5m! optical telescope is the main one in SOLAR-C Plan-B.
–! High throughput with higher resolution. One order of magnitudeimprovement in the spectro-polarimetric sensitivity.
–! The improvement allows us to diagnose chromospheric magnetic fields,
which have been difficult in existing instruments.

1.!

Utilizing the Hanle effect in addition to the Zeeman effect

–!
–!

2.!

The transverse Zeeman effect is not sensitive to magnetic fields
weaker than several hundreds gauss.
The Hanle effect can make significant polarization signals withmagnetic fields weaker than 100 gauss.

High polarization sensitivity of S/N~104–!
–!

In order to observe polarization signals by the joint action of theZeeman and Hanle effect in chromospheres, higher polarization
sensitivity is required.
We can observe magnetic fields of >10 gauss if we can reach thepolarization sensitivity of S/N~104.

Hanle eﬀect in He I 10830 Å
Stokes I

Stokes Q

Stokes U

Stokes V

Zeeman effectHanle effectWhen B>several hundreds gauss, the Zeeman effect is dominating
polarization signals. The Hanle effect becomes significant in the weak
field regime. Amplitudes of the polarized spectral profiles are ~0.1%.

Polarization signals in He I 10830Å
Quiet regions

Active regions

Sunspots

0.0010zation leiralonrp
Linea eeman+HaZ
by tr.

Sensitivity achieved byexisting instruments

0.0100Sensitivity expected to new instrumentsPolarization degree

0.10000.0001

0.1

1.0

10.0

100.0

Field strength (Gauss)

1000.0

Science targets with the diagnostics ofchromospheric magnetic ﬁelds
MHD wave
Flux tube,
Horizontal fields

Spatial scale

Penumbra
micro-jets

Ellerman
bomb,
jets

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acoustic shock

SOLAR-C
4"()'$#0"5'$#+(30+3('#Prominence formationand eruption
Solar cycle

Time scaleScience targets with the diagnostics ofchromospheric magnetic ﬁelds

SOLAR-C

MHD wave

Horizontal fieldspicule
Flux tubea
Penumbra micro-jets

Prominence formationand eruption
Solar cycle

Ellerman bomb, Jets

Ground-based telescopes will
do a good job in the area. Choices of chromospheric lines•! The subWG discussed priority of chromospheric lines
for SOLAR-C in terms of:(1) Good sensitivity to the upper chromosphere(2) Good sensitivity to physical quantities (magneticfields, velocities, and temperatures)•! Diagnostics of mag. fields  •! Diagnostics of dynamics
1.! He I 10830Å
(T, v)
2.! Ca II 8542Å
3.! H" 6563Å

1.! Mg II k 2796Å
2.! Ca II 8542Å
3.! H" 6563Å

Transition region

106K

Photosphere

Chromosphere

Temperature

Ly!

105K

CoronaCIVHe I 10830A
Mg II h/k
HINODE/BFI

UV/EUV spectrograph

Ca II H/K
Ca II 8542Å
H!

Mg I bNa I D1/D2

104K

Fe I
HINODE/SP

100

HINODE/NFISOLAR-CUV-Vis-NIR telescope
10000

Height (km)Candidates of chromospheric linesLine

1.2!/D[arcsec] Photon [/"!/0.1"/sec] Cont.
CenterResponse
height [km]

Zeeman effect
geff

Bl [G]


Bt [G]


HanleeffectMg II k 2796 Å

0.046

2.9x104

2.9x105

~1300

1.17

8.5x101

2.1x103x

Mg II h 2803 Å

0.046

3.1x104

2.5x105

~1200

1.33

7.3x101

1.8x103-

Ca II K 3933 Å

0.065

6.1x105

3.2x105

~940

1.17

6.2x101

1.5x103x

Ca II H 3968 Å

0.065

7.1x105

3.3x105

~980

1.33

5.1x101

1.2x103-

H I # 4861 Å

0.080

1.2x107

1000-2000

1.00
2.00

Mg I b2 5172 Å

0.085

300-600

1.75

Mg I b1 5183 Å

0.086

200-600

1.25

Na I D2 5890 Å

0.097

~370

1.17

Na I D1 5896 Å

0.097

~350

1.33

H I " 6563 Å

0.108

1000-2000

1.00

Ca II 8498 Å

0.140

~680

1.07

Ca II 8542 Å

0.141

~780

1.10

Ca II 8662 Å

0.143

~710

0.83


2.2x102
2.5x102
3.6x102
2.9x102
2.3x102
6.8x102
3.0x102
3.4x102
4.3x102x

300-600
3.7x100
6.5x100
9.6x100
4.7x100
3.4x100
9.7x100
6.3x100
6.7x100
8.4x100

1.2x1030.085


1.5x106
1.1x106
1.0x106
7.9x105
9.2x105
3.0x106
3.8x106
2.4x106
2.4x106

1.6x101

Mg I b3 5167 Å
1.4x107
1.4x107
1.4x107
1.6x107
1.6x107
1.6x107
1.3x107
1.1x107
1.2x107

1.9x106

He I 10830 Å(QS)

0.179

1.9x107

1.8x107

~2000

1.42

1.9x100

3.8x102x

He I 10830 Å(AR)

0.179

1.9x107

1.6x107

~2000

1.42

9.3x100

2.7x102

x

x
x
x
x
-x
x
x
-

Sensitivities to the Zeeman eﬀect•!

Sampling–! Spatial sampling: 0.1"/pix–! Temporal sampling: 1sec–! Wavelength sampling: "/#"=2x105

Formation “height” of spectrum lines
RF Stokes I to Temp
Ca II 8542 Å(by courtesy of H. Uitenbroek)- Response Functions can be used toinvestigate the sensitivity of spectral lines tomodel parameters.
- RFs depend on the atmospheric height andwavelength (2D-functions).
- Centroid of RFs at different wavelengths
provide information on the average sensitivityof spectral lines: “Formation Heights”~ 780 km

Complex formation: H! 6563 Å-! Determining a “formation height” in some
spectral lines is rather difficult. Instead, one
has to talk about “average” formation.

Complex response to T

RF Stokes I to Temp

Photospheric contribution

Other chromospheric lines

Mg I b2 5173

Na I D 5896

Ca II 8542•! Mg I b, Na I D are lines to provide
good diagnostics of the lowchromosphere.
•! Ca II IRT can reach relatively highin the chromosphere.

He I 10830Å
Stokes profiles in EFRPopulation of He I triplet (FAL1993)(by courtesy of R. Centeno and J. Trujillo Bueno)•! High sensitivities to magnetic fields through the Hanle and Zeeman
effect.
•! Easy to interpret because it forms at a thin layer at upper
chromospheric layers by UV irradiation) without affected photosphericand low chromospheric atmospheric condition.
•! The diagnostics methodology with the line is being matured.

Mg II k/h to reach higher chromosphere
Mg II k 2796 Å

Ca II k 3933 Å•! Higher opacity in Mg II k/h than Ca II H/K, which allow us to reachhigh in the chromosphere.
•! Lower continuum intensities, which allows us high contrast imagingof the chromosphere without affected by photosphericcontamination.
•! Ground-based observations cannot access the line.

Mg II k/h to reach higher chromosphere
Mg II k 2796 ÅCa II k 3933 ÅCa II 8542 Å•! Higher opacity in Mg II k/h than Ca II H/K, which allow us to reachthe higher chromosphere.

•!

Sampling–! Spatial sampling: 0.1"/pix–! Temporal sampling: 1sec–! Wavelength sampling: "/#"=2x105

High throughput to be achieved withthe 1.5mϕ telescope•! S/N~104 for high precision spectro-polarimetry–! Ca II 8542Å: 0.18"/pix, ~10sec integration–! He I 10830Å: 0.18"/pix, 3-10sec integration•! S/N~102 for high-speed spectroscopy–! Mg II k 2796Å: 0.06"/pix, <0.5sec integration–! Ca II 8542Å: 0.06"/pix, <0.1sec integration

NIR detector for SOLAR-C•!

For observing He I 10830Å in SOLAR-C, a NIR detector is essential toachieve high throughput for chromospheric diagnostics.

•!

The QE of Si CCD is less than 10% at 1.08µm, which is almost one order ofmagnitude smaller than the efficiency of NIR detectors. The merit of the large
throughput with the 1.5m" aperture in SOLAR-C is significantly reduced if we
use the CCD.
8542Å 10830Å
!
!

Example of QE of CCD•!

One of the technical issue is that a NIR detector has to be cooled down toachieve low dark currents. In ground-based observation, LN2 is used to cool adetector down below 100K. But a coolant cannot be used in a space mission.
It is difficult to use a cryocooler because it causes significant disturbances anddegrades image quality. # of photo-charges inSOLAR-C > 106 /pix/sec
Photon noise $ > 103

Requirements to the instruments•! Spatial resolution–! ~0.2” for magnetic field diagnostics with high S/N (photon noiselimited).
–! Diffraction limited resolution (0.05” with 1.5m") for intensity andvelocity diagnostics with lower S/N.

•! FOV–! 200”x200” to cover medium size active region.

•! Spectral resolution
–! %/&%>100,000 to resolve thermal widths of chromospheric lines.

•! Polarimetric sensitivity
–! Photometric sensitivity of (1-3)x10-4, instrument polarization
calibrated with the order of 10-3.

•! Two dimensional spectroscopic capability–! A single slit spectrograph is not adequate to investigate rapid
evolution of chromospheric dynamics.

Eﬀective area

Ag coating

Al coating