the solar dark energy problem -- measuring coronal magnetic fields and our infrared frontier

The Solar Dark Energy Problem -- Measuring Coronal Magnetic Fields and Our Infrared Frontier

• 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

J.R. Kuhn, Associate DirectorInstitute for Astronomy

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

0.5m 4.0m

Diffraction

Mirror roughness

Atmospheric backgrounds

SOLAR-C

M1: 0.5m F/3.7

M2

Gregorian focus8m f.l.

F/20, efl 8m, prim-sec 1.7m0.5m, 1.5m fl primary55mm, secondaryl/10 p-v figurediff. Limited @ 1micron over 15’fov10.4 deg tilt angle

SOLAR-C Optics

Measured secondary PSF

Over 5 orders of magnitudeno mirror or other spuriousscatter terms detected

Short exposure imagesnearly diffraction limited

l = 656 nm

“blue” disk photometry

IR expectations

• Judge, Casini, Tomczyk, Burkepile...(http://comp.hao.ucar.edu/how.html)

Ion Wavelength Temperature ProspectsFe XIV 530.3nm 2MK okFeXIII 1075nm 1.7MK excellentSi X 1430nm 1.3MK okMg VIII 3027nm 0.8MK ?Si IX 3932nm 1.1MK goodMg VII 9031nm 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

LCVR Polarimeter

Input array of fiber optics bundle

Re-imaging lens

Prime focus inverse occulter/field stop

Secondary mirror

Primary mirror

Fiber Bundle

Collimator

Echelle Grating

Camera Lens

NICMOS3 IR camera

April 6 2004 Observations

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.

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 & UStokes Q & U Scan:• RV = 0.25 R • From PAG 250° to 270°• Five 5° steps

Lin et al. (in press)

IR Spectropolarimetry

FeXIII IR Coronal PolarimetryI Q

U V

B=4.6G

IR Coronal Stokes V

Results: Coronal Magnetograms

B=4,2,0,-2 G

Coronal model B comparison

From MURI CollaborationAbbett, 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 KuhnOahu, IR solar physics

Dr. Jing LiOahu, Magnetic fieldstudies

Dr. Don MickeyOahu, Solar InstrumentationMagnetic field studies

Prof. Shadia HabbalSolar, 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

SDO 2008-13 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

NEXUS 2006-08 Spec 45-65nm 0.5 0-2.0

ATST 2012-52 (several) Filter, Spec, Pol, pB

1000-28000nm

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

d blur

y astig.

f / y coma

:TransverseOrder Third

2

2

dy

Q

f

e

For small angles, Q, blur is astigmatic and only weaklydependent on off-axis distance. SOLARC is diffraction limitedover 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

M1: 0.5m F/3.7

M2

Gregorian focus8m f.l.

F/20, efl 8m, prim-sec 1.7m0.5m, 1.5m fl primary55mm, secondaryl/10 p-v figurediff. Limited @ 1micron over 15’fov10.4 deg tilt angle

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

BBSOUHKorea

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 ParametersAperture: 4m Optical configuration:

Gregorian, off-axis

Mount Alt-Az Enclosure Ventilated co-rotating “hybrid” dome FOV: 3 arcmin minimum, goal of 5 arcmin Image Quality: Conventional AO Case:

Diffraction limited within isoplanatic patch. MCAO (upgrade option): Diffraction limited over > 1 arcmin FOV Seeing Limited Case: <0.”15 over 3 arcmin FOV (λ=1 μm )

Adaptive Optics: Strehl (500nm): >0.3 median seeing, >0.5 good seeing

Wavelength Coverage:

300 nm - 28 m

Polarization Accuracy:

Better than 10-4 of Intensity

Polarization Sensitivity

limited by photon statistics down to 10-5 Ic

Coronagraphic: In the NIR and IR Scattered Light: <10-5 at r/rsun = 1.1 and >1μm

1.6 microns)

Telescope Optics

• 3-5 arc minute field– Few percent of solar disk

Figure 2. Prime Focus Heat Stop

DM

CollimatorM1

M2

• F/13 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

QQ+U

B

03

13

23

P

P

P

13

13

S

P

)10(10 1

)108.1(1G

172

17L

sA

smceB

L

)10A 1083nm, HeI (eg.

Hanle)(A Permitted 17

L

s

E

VUQ,

profile) dI/d(almost BV

profile) Ith (almost wi B UQ,

)10A 1075nm, FeXIII eg.(

)(AForbidden 12

L

s

)( BV

B oft independen UQ,

los B toor ison polarizati

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

Ongoing Coronal B efforts

• COMP, Ground-Based Coronal Research Project (HAO lead)

• ATST (NSO)

• SOLARC (IfA)M1: 0.5m F/3.7

M2

Gregorian focus8m f.l.

F/20, efl 8m, prim-sec 1.7m0.5m, 1.5m fl primary55mm, secondaryl / 10 p-v figurediff. Limited @ 1micron over 15’fov10.4 deg tilt angle

SOLAR-CCoMP: Coronal MultichannelPolarimeter (HAO)

• FeXIII filtergraph polarimeter

• Sac Peak 20 cm “One Shot”Coronagraph

• 1024x1024 Rockwell IR detector

• 1.5 R field-of-view

• 5.6” pixels

• Augment with spectroscopy atEvans

• First measurements in 2003

SOLARCRoy Coulter, Jeff Kuhn, Haosheng Lin, Don Mickey

100nm spectrographfilter bandpass

3.93 micron

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

• Radon transform using Algebraic Reconstruction Technique

)sin( )cos( 0)sin(cos

)sin),(cos),((),(

111

1

loszlosy

zy

BBBB

sBsBzyB

s

Q

z

y

The projection problem

The inversion

10 iterations over 12 projectionsspaced 15 degrees...

Another inversion

6 projections, 0-90 degrees...

Potential field...

Long Wavelengths

SOLARCPrime orGregorian Focus

chop Warm IRSpectrograph

Fast 1-5muIR Camera

Cold Narrow-band filter