The Solar Dark Energy Problem - Measuring Coronal Magnetic
Fields and Our Infrared Frontier
J.R. Kuhn, Associate Director
Institute for Astronomy
• We know relatively less about the solar IR
spectrum, but it is very important for future
coronal observations
• Our newest telescopes and instruments on
Haleakala are aimed at measuring these
fields
Pictures aren’t enough:
(from Chen et al., Low, Gibson, Roussev et al.)
SOLARC: Why an IR
(reflecting) off-axis coronagraph?
• Zeeman magnetic sensitivity
• Lower scattered sky background
• Lower scattered instrument optics
background
• Lowered scattered dust background
Ideal B measurement sensitivity
5 min observation, 10” pixel
Scattering sources
• Atmosphere
– “seeing”
– aerosols
– atomic molecular scattering
• Telescope
– diffraction
– mirror roughness
– mirror dust
Optical backgrounds
Mirror
roughness
Diffraction
0.5m
4.0m
Atmospheric backgrounds
SOLAR-C
Gregorian focus
8m f.l.
M2
F/20, efl 8m, prim-sec 1.7m
0.5m, 1.5m fl primary
55mm, secondary
l/10 p-v figure
diff. Limited @ 1micron over 15’fov
10.4 deg tilt angle
M1: 0.5m F/3.7
SOLAR-C Optics
Measured secondary PSF
Over 5 orders of magnitude
no mirror or other spurious
scatter terms detected
l = 656 nm
Short exposure images
nearly diffraction limited
“blue” disk photometry
IR expectations
• Judge, Casini, Tomczyk, Burkepile...
(http://comp.hao.ucar.edu/how.html)
Ion
Wavelength
Fe XIV 530.3nm
FeXIII 1075nm
Si X 1430nm
Mg VIII 3027nm
Si IX 3932nm
Mg VII 9031nm
Temperature Prospects
2MK
ok
1.7MK
excellent
1.3MK
ok
0.8MK
?
1.1MK
good
0.6MK
?
The IR corona
Kuhn et al. 1995, 1999
Also Judge et al., 2002
The IR Coronal triple
whammy
• Magnetic sensitivity increases with
wavelength
• All significant scattered light sources
decrease with wavelength (mirror, dust,
atmosphere)
• Bright CELs and atmospheric opacity
windows coincide
SOLARC Lessons
Secondary mirror
Prime focus inverse occulter/field stop
Re-imaging lens
LCVR Polarimeter
Input array of fiber optics bundle
Primary mirror
Echelle Grating
Camera Lens
Collimator
NICMOS3 IR camera
Fiber Bundle
April 6 2004 Observations
Full Stokes vector observations were obtained on
April 6, 2004 on active region NOAA 0581 during
its west limb transit.
Stokes I, Q, U, & V Observation:
•
20arcsec/pixel resolution
•
70 minutes integration on V
•
15 minutes integration on Q & U
Stokes Q & U Scan:
•
RV = 0.25 R
•
From PAG 250° to 270°
•
Five 5° steps
Lin et al. (in press)
Fe X 171Å image of the solar corona at approximately the time of
SOLARC/OFIS observation from EIT/SOHO. The rectangle
marks the target region of the coronal magnetic field (Stokes V)
observation.
IR Spectropolarimetry
FeXIIII IR Coronal Polarimetry
Q
B=4.6G
U
V
IR Coronal Stokes V
Results: Coronal
Magnetograms
B=4,2,0,-2 G
Coronal model B comparison
From MURI Collaboration
Abbett, Ledvina, Fisher,…
These observations
Trace EUV ‘Poster’ Image
What light’s up the loops?
Conclusions
• Coronal field measurements are feasible
with current technology
• Fundamental limitations to spatial and
temporal resolution will persist until we
have larger aperture coronal telescopes
• These capabilities are coming
Ground-based Coronal Research:
Why and Where?
Institute for Astronomy, Mees,
Haleakala Observatory
Prof. Haosheng Lin,
Maui, IR solar physics
Prof. Jeff Kuhn
Oahu, IR solar physics
Dr. Don Mickey
Oahu, Solar Instrumentation
Magnetic field studies
Dr. Jing Li
Oahu, Magnetic field
studies
Prof. Shadia Habbal
Solar, solar terrestrial
Haleakala Observatory
Haleakala Future
• Ground-based coronal and high resolution
physics
• New technologies for telescopes and
infrared detectors
Our “dark energy” problem
Ground-based coronal
science?
Corona: Space -Complementarity
MISSION
DATES
INSTR.
TYPE
WAVE
ARCSEC per
PIXEL
FOV
SOLARB
2005-08
EIS
Spec.
17-29nm
1.0
0-1.4
STEREO
2006-10
COR1/COR2
pB
Broadband
(450-750nm)
7.6-14
1.1-15
EUVI
Spec.
17-30nm
1.3
0-1.4
AIA/
Magritte
Filter
7 channels
20-122nm
0.66
0-1.4
AIA/Spectre
Spec.
(one line)
O V 63nm
0.6
0-1.2
KCOR/ECOR
pB
Broadband
(450-750nm)
7.6-14
1.4-15
Spec
45-65nm
0.5
0-2.0
SDO
2008-13
NEXUS
2006-08
ATST
2012-52
(several)
Filter, Spec,
Pol, pB
100028000nm
0.1
1.05-2.6
SOLAR
ORBITER
2012-18?
(several)
pB, EUV
Spec?
(several)
(in situ)
(in situ)
Stellar Differential Image Motion
Seeing Tests at Haleakala
Observatory Seeing Comparison:
Solar Seeing Site Survey
Measurements
Sky brightness measurements
ATST SSWG Top Site
Characteristics Summary
Why off-axis telescopes?
• Pupil is filled and unobstructured – high
order adaptive optics uncorrupted
• Pupil is constant in altitude-azimuth optical
configuration
• Secondary heat removal and optics are
accessible
• Scattered light and image contrast are
higher
Telescope pupil and wavefront errors
Off-axis telescopes
Off-axis angle
Off-axis telescope “myths”
• “Aberrations are worse than conventional
telescopes”
• “They can’t be aligned”
• “Large off-axis mirrors aren’t
manufacturable”
Aberrations
• This is not an asymmetric optical system, it
is a “decentered” system
• The full aperture is not illuminated
Q
dy
e
Third Order Transverse :
coma
  y 2 / f
astig.
blur
  y 2
 d
f
For small angles, Q, blur is astigmatic and only weakly
dependent on off-axis distance. SOLARC is diffraction limited
over 15 arcmin field
A new generation of low-scattered light
coronagraphic and adaptive optics
telescopes
• SOLARC (UH)
– Coronagraph, 0.5m, 10.5 deg off-axis
• New Solar Telescope
(BBSO/UH/KAO/Others?)
– Disk, 1.7m, 30 deg off-axis
• Advanced Technology Solar Telescope
(NSO/UH/NJIT/HAO/UChic+others?)
– Coronagraph/disk, 4m, 32 deg off-axis
SOLAR-C
Gregorian focus
8m f.l.
M2
F/20, efl 8m, prim-sec 1.7m
0.5m, 1.5m fl primary
55mm, secondary
l/10 p-v figure
diff. Limited @ 1micron over 15’fov
10.4 deg tilt angle
M1: 0.5m F/3.7
SOLARC Status
• Worlds largest solar coronagraph
• Used for IR coronal studies
– Coronal Magnetic fields
• Imaging Fiber Bundle Spectrograph and
spectropolarimeter
• SOLARC demonstrates the potential of an
optically fast off-axis optical telescope, new
coronal studies underway, collaborators
welcome
The New Solar Telescope
BBSO
UH
Korea
NST Concept
NST Concept
Sketch of the NST showing the optical path, optical support structure, and primary mirror cell.
Only the top floor of the observatory building is shown, since the existing dome will be
replaced to fit the telescope envelope and provide better means of wind flushing and overall
thermal control.
Optics will “pace” the project
The 10 cm thick primary mirror of the NST is made from Zerodur and has a 1.7 m diameter. It was shaped
and configured by EASTMAN KODAK and has been shipped to the Steward Observatory of the
University of Arizona, where it awaits polishing. The concave surface radius of the off axis parabola is
8140 mm with a conic number of -1.0, a vertex radius of 7700 mm, and an off-axis distance of 1840 mm.
NST Status
• Mirror awaiting UA mirror lab secondary
polishing system, begin Dec. 2004, end July
2005
• Dome replacement detailed optical support
structure design and construction under way
• International collaborators welcome
Advanced Technology Solar
Telescope
• PI:
– Steve Keil
• Co-PI’s
–
–
–
–
Michael Knoelker (HAO)
Jeff Kuhn (IfA)
Phil Goode (NJIT)
Bob Rosner (Univ. Chicago)
• NSO ATST Staff
– Thomas Rimmele (Project
Scientist)
– Jeremy Wagner (Interim
project manager)
Formal collaborators:
USAF (Richard Radick, Nathan Dalrymple)
The University of Rochester (Jack Thomas)
California Institute of Technology (Paul Bellan)
California State College, Northridge (Gary Chapman, Christina Cadavid, Steve
Walton)
Michigan State University (Bob Stein)
Stanford University (Alexander Kosovichev)
Montana State University (Dana Longcope)
Princeton University (Frank Cheng)
University of Colorado (Tom Ayres, Juri Toomre)
University of California, San Diego (Bernard Jackson, Andy Buffington)
Lockheed Martin (Tom Berger, Alan Title, Ted Tarbell)
NASA Marshall Space Flight Center (John Davis, Ron Moore, Alan Gary)
NASA Goddard Space Flight Center (Don Jennings)
University of California, Los Angles (Roger Ulrich)
Colorado Research (K. D. Leka)
Harvard-Smithsonian CFA (Ballegooijen, Nisenson, Esser, Raymond)
Southwest Research Institute (Craig Deforest, Donald Hassler)
International Partners being sought – involvement through SWG and site work now
System Parameters
Aperture:
Optical
configuration:
Mount
Enclosure
FOV:
Image Quality:
Adaptive Optics:
Wavelength
Coverage:
Polarization
Accuracy:
Polarization
Sensitivity
Coronagraphic:
Scattered Light:
4m
Gregorian, off-axis
Alt-Az
Ventilated co-rotating “hybrid” dome
3 arcmin minimum, goal of 5 arcmin
Conventional AO Case:
Diffraction limited within isoplanatic patch.
MCAO (upgrade option):
Diffraction limited over > 1 arcmin FOV
microns)
Seeing Limited Case: <0.”15 over 3 arcmin FOV (λ=11.6
μm
)
Strehl (500nm): >0.3 median seeing, >0.5 good seeing
300 nm - 28 m
Better than 10-4 of Intensity
limited by photon statistics down to 10-5 Ic
In the NIR and IR
<10-5 at r/rsun = 1.1 and >1μm
Telescope Optics
• 3-5 arc minute field
– Few percent of solar disk
M2
Figure 2. Prime Focus Heat Stop
• F/13 collimator
DM
M1
Collimator
– 200 mm collimated beam
• Elevation and Azimuth axis
• Deformable mirror at pupil
Primary Mirror Assembly
• 4.3 meter substrate
– 100 mm thin meniscus
– Low expansion material
• 120 active supports
• Forced cooled air
temperature control
ATST Status
• Design and development proposal (11M$) ends
during 2005
• Construction phase proposal (161M$) now being
considered by NSF and US National Science
Board. Major funding start date late 2006 or early
2007
• International partners sought
• ATST Science working group (as of 10/14/04) has
recommended a primary site for the ATST –
Haleakala, and backup sites (LaPalma and BBSO)
Summary
• Measured by major new facilities, solar
astrophysics is on the verge of healthy
growth – competing and attracting resources
in the US community comparable to the
much larger nighttime astronomical science
community.
Magnetic linear polarization sensitivity
B
Q
Q+U
 L  eB mc (1G   L  1.8  107 s 1 )
1 A

(102  107 s 1 )
Permitted (A   L )  Hanle
Forbidden (A   L )
(eg. HeI 1083nm, A  107 s 1 )
(eg. FeXIII 1075nm, A  102 s 1 )
3
3
P1
S1
E
Q, U  B (almost with I profile)
V  B (almost dI/d profile)
Q, U  V
3
P2
3
P1
3
P0
Q, U independent of B
V  Blos (  )
polarization is or  to B
Coronal Hanle measurements
• Raouafi, Sahal-Bréchot, Lemaire, A&A
396, 1019, 2002.
– OVI 103.2nm polarization measurement using
CDS in a coronal hole (9%, 9 degree from limb
tangent)
– Analysis: non-unique solution requires both B
of a “few gauss” and velocity of “few 10’s
km/s”
QU forbidden line observations
• Habbal, Woo, Arnaud, Ap.J.
558, 825, 2001
– FeXIII HAO/NSO KELP
project 1980’s
Coronal forbidden line Zeeman
Observations
• Lin, Penn, Tomczyk, ApJ, 541, L83 (2000)
– FeXIII V polarimetry
SOLAR-C
CoMP: Coronal
Multichannel
Ongoing
Coronal
B efforts
Polarimeter
(HAO)
• FeXIII filtergraph polarimeter
•
COMP,
Ground-Based
Gregorian focus
• Sac Peak 20 cm “One
8m f.l. Shot”
Project (HAO lead)
Coronagraph
M2
• 1024x1024
• ATSTRockwell
(NSO)IR detector
• 1.5 R field-of-view
• 5.6” pixels
• SOLARC
(IfA) at
• Augment
with spectroscopy
Evans
F/20, efl 8m, prim-sec 1.7m
0.5m, measurements
1.5m fl primary
• First
in 2003
55mm, secondary
l / 1 0 p-v figure
diff. Limited @ 1micron over 15’fov
10.4 deg tilt angle
Coronal Research
M1: 0.5m F/3.7
SOLARC
Roy Coulter, Jeff Kuhn, Haosheng Lin, Don Mickey
3.93 micron
100nm spectrograph
filter bandpass
Magnetic field measurements...
• ...will be achieved in the quiet corona with a
sensitivity of better than 1 G
• ...from IR coronal observations obtained by
several research groups using sensitive
polarimetry techniques
• ...on a timescale of one year
Vector Inversions
• FF and potential model from Low (1993)
– External potential field+FF at r<R + dipole
z
• Radon transform using Algebraic
Reconstruction Technique
y
Q
B( y, z )  1 ( By ( s, ) cos  Bz ( s, ) sin  )
1 (cos sin  )  0 By  1 ( Blos cos ) Bz  1 ( Blos sin  )
s
The projection problem
The inversion
10 iterations over 12 projections
spaced 15 degrees...
Another inversion
6 projections, 0-90 degrees...
Potential field...
Long Wavelengths
SOLARC
Prime or
Gregorian
Focus
chop
Warm IR
Spectrograph
Fast 1-5mu
IR Camera
Cold Narrow-band filter