Institut d’Astrophysique Spatiale

LYOT: LYman Orbiting Telescopes
Jean-Claude Vial (PI) et Frédéric AuchèreInstitut d’Astrophysique Spatiale
and The LYOT Team Project:
Frédéric Rouesnel, Thierry Appourchaux, Michel Berthé, Bernard Cougrand,
Catherine Cougrand, Cydalise Dumesnil, Philippe Duret, Jean-Jacques
Fourmond, Jean-Christophe Le Clec’h, Benjamin Lustrement, Anne Millard,
Gilles Morinaud, Guillaume Prévôt and Xueyan Song-Zhang

November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique Spatiale

Main Scientific Objectives• Energy release and the Initiation of Coronal Mass Ejections (CMEs)

Several models (e.g. flux rope, Amari et al. 2003, breakout
Aulanier et al. 2001)

None are totally satisfactory How is the magnetic energy stored ? Field topology ?
 What triggers the instability ? Precursors ?
 At what height does the magnetic reconnection occur ?
To answer these questions, one needs to observe the region,
unobserved today, of CME initiation• Energy transport during flares• Large-scale current sheets in the corona
November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique SpatialeComplementary Scientific Objectives• Measurements of the coronal magnetic field
Hanle effectBommier & Sahal (1982)• The chromosphere-corona interface

Further studies of interest••November 19, 2008

Spatial and temporal variability of the Lyman α irradiance
Origin of solar energetic particles
Solar-C science definition meeting

Institut d’Astrophysique Spatiale

Why Lyman α ?
Chromosphere

Filaments, prominences,
spicules, flares, etc.

cold

Chromosphere – corona coupling

CoronahotCMEs, prominence
eruptions,current sheets, plasmoids,etc.
B: Hanle effectNovember 19, 2008Solar-C science definition meeting

Institut d’Astrophysique Spatiale

Other advantages of Lyman α
 Factor 1000 gain on the disk / corona contrast
 Access to the inner corona (1.15 R) High resolution imaging (low scattered light)
 No F corona (dust)

10-2
Modélisation Ly

10-4

-6
10

-8
10

Equateur Lyα(UVCS)

Trou coronalLyα(UVCS)

Equateur lumièr eblancheTrou coronal lumi
ère blanche-10
10
1.0
1.5
2.0
2.5
3.0
Distance au centre du Soleil (Ro)November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique Spatiale

LYOT performances specifications
Specifications

LADI

LACI

Wavelength

121.6 nm121.6 nm

FOV

1.2 Rs1.15 Rs to 2.5 Rs

Spatial resolution

1.12 arcsec / pixel

2.35 arcsec / pixel

Dynamic range

3 104

7 105

Spectral purity

>95%

>90%

0.2 s to 20 s

2 s to 120 s

Watching & event

Watching & event

SNR (photometry + electronics + compression)>10>1 at 2.5 Rs

Polarisation

N/A

Scattered light< signal across the FOV< signal across the FOV

Absolute calibration

10%

30%

Pointing accuracy

<29’’

<29’’

Pointing stability0.4’’ over exposure time (1σ)

0.8’’ over exposure time (1σ)

November 19, 2008

Solar-C science definition meeting

Cadence
Observing modes• Rs min = 25% for photometry• Rp/Rs = 4. 10-3
• Possibility of total brightness images

Institut d’Astrophysique Spatiale

LYOT OPTICAL DESIGNLACI – DESIGN

Aperture size: 40 mm

Internally occulted coronagraph (Lyot)

Field of View: 1.15 to 2.5 Rs (0.307°to 0.668°)
Optical layout and focal length:
540 x 260 x 90 (mm3) and 900 mm- No loss of resolution- More compact- Stray-light

Focal plane resolution: 2k x 2k withpixel size 10 µm x 10 µm
Pixel area equivalent FOV: 2.35 arcsec
Design constraints:• reflective optics• superpolished first optics coated

LACI Raytracing• cleanliness

November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique Spatiale

LYOT OPTICAL DESIGNLACI / POLARIZER – DESIGN 1/2

Main drivers:- Rs min : better than 25%- Rp/Rs: better than 4 10-3
- Angle of acceptance: Rs min & Rp/RS fulfilled on FOV- Capability to perform both polarized and unpolarized
imagery

MgF2	Al	MgF2	

Al2O3 (0.8 nm)	Optical features:

Al	

1.0
Réflectivité Rs, Rp- M5 : flat mirror composed of two segments with different
coatings (multilayers with MgF2/Al) for polarized/unpolarized
imageryi = 62°
Rs = 0.75-3
Rp = 1.6 10

0.8
0.6
0.4
0.2
0.0
020

4060
Angle d'incidence (deg)80i = 62° Rs = 0.75 Rp = 1.6 10-3
Rp/Rs = 2.13 10-3
UV Polarizer Development
for test @ Fracasti

November 19, 2008

Solar-C science definition meetingInstitut d’Astrophysique Spatiale

LYOT OPTICAL DESIGNLADI - DESIGN

Aperture size: 40 mm
Field of View: 0 to 1.2 Rs (0° to0.32°)
Optical layout and focal length: 500 x
90 x 40 (mm3) and 3960 mm
Focal plane resolution: 2k x 2k withpixel size 22µm x 22 µm
Pixel area equivalent FOV: 1.12
arcsec

LADI Raytracing

Spectral selection: obtained by using
two Lyman α filters

November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique Spatiale

LYOT Overview
LACI	  op(cal	  box	  Detector	  radiators	  Pupils	  Detectors	  electronics	  box	  Mechanisms	  electronics	  box	  Monopod	  Light	  trap	  radiator	  Door	  Filter	  radiator	   SES	  Bipod	  Electronics	  radiator	  LADI	  op(cal	  box	  Op(cal	  bench	  sandwich	  Panel	  C\Al\C	  November 19, 2008

Solar-C science definition meeting

Institut d’Astrophysique Spatiale

Conclusions
 LYOT answers keys issues in solar physics
Initiation / propagation of CMEs
Structuring role of the coronal magnetic field
Chromosphere / corona coupling Unique capabilities
First images of the Lyman α corona since 1970
Continuous disk / corona observations at Lyman α	First continuous measurement of the coronal magnetic field

November 19, 2008

Solar-C science definition meeting