Blue Dot Team

« Multi aperture imaging »

BDT - 16-17 sept 20082

MAI techniques

• High accuracy visibility measurement

• Differential interferometry

• Nulling interferometry

• Hypertelecopes and pupil densification

BDT - 16-17 sept 20083

Nulling interferometry : principles

Beam combiner

T2T1

DD.sin

Star Planet

+1 arcsec

=10m, D=10m, =0.1 arcsec

BDT - 16-17 sept 20084

Nulling interferometry : key issues• Phase matching

– Co-phasing of the wavefront : optical delay lines + fringe sensor

– Perfect coherence of the stellar wavefront : optical filtering + AO if necessary

• Polarization matching– Control of polarization rotation over the

optical bench

• Amplitude matching

BDT - 16-17 sept 20085

Nulling interferometry : requirements

Hot Jupiter

Ocean planet

Real Earth

Real Jupiter

Uranus

Distance to the star (mas)

5 100 100 520 2000

Baseline (m) 20

150

400

1

7

20

1

7

20

0.2

1.4

4

0.05

0.4

1

Total flux (mJy) 0.86

2.16

1.1

3 e-4

1 e-4

1.3 e-3

3 e-5

1 e-5

1 e-4

5 e-5

1.5 e-5

3 e-5

5 e-7

1.5 e-7

2 e-8

Contrast star/planet

35000

4000

1200

1e+8

1e+8

1e+6

1 e+9

1 e+9

1e +7

6 e+8

6 e+8

4 e+7

7 e+10

7 e+10

7 e+10

• Planets around a G0 Star at 10 pc

• V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands

BDT - 16-17 sept 20086

Observing an Earthlike planet :A few interesting photons … a lot of noise

Signal : ~ 10 ph s-1 m-2 (in the [6-20 m] spectral range)

background and noise

Stellar leaks (star size + pointing stability)Vary as 2 to 6 (and more cf. Rouan)

IR background (locl zodi + instrument emission

Exo-zodi (global emission x interferometre response)

~ 10 to 100 x Signal

~ 1000 x Signal

~ 300 x Signal

BDT - 16-17 sept 20087

Nulling interferometry : several concepts

Angel et al. 1989Mennesson et al. 1997

BDT - 16-17 sept 20088

Internal modulation (Mennesson et al. 2005)

/2

/2

Detector

Detector

Sub-arrays Transmission map 4

transmissioncentral symmetry conjugaison

Modulation efficiency

- Contribution of Exo-zodi and stellar leaks are the same in the 2 states of modulation- Fast modulation (faster than rotation) post détection.

BDT - 16-17 sept 20089

Nulling interferometry : what is observed ?

• Single pixel detector signal with:– Planetary signal (modulated)– Mean stellar leaks (not modulated)– Mean exo-zodi signal (not modulated)– Local zodi (not modulated)– Variable stellar leaks (pointing + asymmetry of the star)

(variable)– Variable exo-zodi signal (asymmetry of exo-zodi)– Other sources of noise (thermal noise, detection noise,

instrumental noise…)

• Image reconstruction software necessary to get F(α,δ,λ), using multi (baseline + λ) information: cf. E.Thiébaut et al.

BDT - 16-17 sept 200810

« Scientific products of nulling interferometry

(After Mennesson et Mariotti 1997)

« Imaging » Spectral analysis

BDT - 16-17 sept 200811

Nulling interferometry in the lab (and in the world)

BDT - 16-17 sept 200812

Stability of the null

• 1/F noise• Need for a control loop to stabilize the null• Control loop based on the interferometric signal

instead of metrology signal (to avoid differential effects).

BDT - 16-17 sept 200813

Stability of the null

ddm

ddm

N

t

t

N2 N3N1

N

BDT - 16-17 sept 200814

Nulling interferometry : requirements

Hot Jupiter

Ocean planet

Real Earth

Real Jupiter

Uranus

Distance to the star (mas)

5 100 100 520 2000

Baseline (m) 20

150

400

1

7

20

1

7

20

0.2

1.4

4

0.05

0.4

1

Total flux (mJy) 0.86

2.16

1.1

3 e-4

1 e-4

1.3 e-3

3 e-5

1 e-5

1 e-4

5 e-5

1.5 e-5

3 e-5

5 e-7

1.5 e-7

2 e-8

Contrast star/planet

35000

4000

1200

1e+8

1e+8

1e+6

1 e+9

1 e+9

1e +7

6 e+8

6 e+8

4 e+7

7 e+10

7 e+10

7 e+10

• Planets around a G0 Star at 10 pc

• V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands

BDT - 16-17 sept 200815

2 types of concepts

• Preparatory science concept : hot jupiters, brown dwarfs, exo-zodi characterisation– 2 telescope array, Contrast 10-4, near IR, stability 10-5 no internal

modulation = state of the art nulling performance

• Characteristation of exo Earths– Multiple telescope arrray, internal modulation, Contrast 10-6,

Thermal IR, stability 10-9

Only concept 1 has been studied from ground and space using space agencies standards

BDT - 16-17 sept 200816

Missions requirementsCharacteristics Prep Sci. Concept Char. Of Earth concept

Spectral band Near IR Thermal IR

Cophasing accuracy (residual opd)

2.5 nm rms 3 nm rms

Interferometric extinction

10-4 10-6

Nulling stability 10-5 10-9

Dephasing accuracy 5 10-3 rad 10-3 rad

Baseline 10-500 m 20-500 m

Satellite guiding A few arcsec A few arcsec

Fine guiding 20 mas 8 mas

Telescope size 30-40 cm 1-3 m

Instrument T 100 K 40 K

Detector T 55 K +/- 1K 10 K

BDT - 16-17 sept 200817

Concept 1 : From the ground : GENIE and ALADDIN

• Need fr a quiet site : Antartica (ALADDIN) vs Paranal (GENIE) . Absil et al. 2008

• Presence of the atmosphere (background + turbulence) -> choice of the spectral range and observation strategy

• Compatibility with existing facilities (VLTI)• Reduced cost compared to space (TBC for

Antartica)

BDT - 16-17 sept 200818

Concept 1 : from space : PEGASE mission concept

BDT - 16-17 sept 200819

MAIN FUNCTIONALITIES OF THE PAYLOAD

Spectrodetectors

55 K detection stage +fiber coupling (,

2.5 nm rmsstability zone

optical head internal laser

metrology

z2

FRAS 1+2 1.0-1.5 µm

resolution on the sky

30 mas

pupil plane 2

beam compressor

D 1

Fringe sensor1+2

0.6–1.0 µm2 nm resolution

I2I1

combining stagephase shift

dODL 11 cm

stroke1 nm

resolut.

ODL 2

Siderostat 1

O 1

D’

O1

Siderostat 2

O2

M

1

O2

combiner

pupil plane 1

beam compressor 1G=D/dD

BDT - 16-17 sept 200820

HD 209458 (d=47 pc, k=4,39)

1,00E-02

1,00E-01

1,00E+00

1,00E+01

1,00E+02

1,00E+03

1,5 2 2,5 3 3,5 4 4,5 5 5,5 6

Longueur d'onde en µm

SNR*

Shot

SNR*

SNRth

SNRdark

SNR total

SNR IN NULLING MODE (hot jupiters case)

nulling instabilty due to :opd stab. : nm rmsflux balance stab. : % rms(pointing stability)

detector noise <Td> et Td + RON

optics thermal noise<To> et To

photon noiseintegration time i

mi

n

ma

x

SNR min in [min max]

parameters :i=10h, D=30 cm, o=0.1, q=0.6, <Td>=55°K, Td=0.1°K rms, <To>=100°K, To=1°K rms, ><510-3 rad, <> < 0.01, =2.5 nm rms, =0.003 rms, RON 10e-

BDT - 16-17 sept 200821

Concept 1 : Payload composition

• Beam transportation• Fine Relative Angle

Sensor + tip-tilt mirror• Optical delay line• Achromatic phase shifter• Optical filtering stage• Beam combining stage• Detection stage

Equipment TRL Note

Hg-Cd-Te matrix 9 Picnic on board HST. In-As-Ga photodiode 9 Used on board SPOT4 for the MIR channel e2v CCD or HAS 4 TRL 9 at usual temperatures, bu t

qualification to 90 K required PZT TTM 4 Idem DL 5 TPD-TNO 40 K tested ODL [9] APS 4 Dispersive or reflective APS tested on

ground with 10-4 to 10-5 nulling level Cesic bench 7 NIRSpec bench, cryo test, MMZ 3 Proved 10-4 null in Synapse breadboard in

K band. Extended MMZ to be tested in Persee in 2008

Optics 9 Gold coating on flat or parabolic smal l mirrors (< 40 cm)

Monomode fibres 4 Compatibility with space an d 90 K to be addressed.

BDT - 16-17 sept 200822

Concept 1 : Mission requirements

• Variable baselines : – formation flying : 2 siderostats and a beam combining lab satellite

– cold gas thrusters

– 2 stage metrology (RF + optical sensor)

– Fine metrology using the payload signal

• Thermal control of the instrument : V grooves • Launch at L2• Operations at L2• Cost estimate : 300 M€ (mission) + 80 M€ (payload)

Equipment TRL Note Thrusters 4 Improvement of existing thrusters with TRL 8 Radio frequency metrology 4 Will be tested in flight with Prisma in 2009 Optical sensor 4-7 CNES R and D at Sodern Free flying GNC 4 First levels tested on Prisma in 2009 Precise ST 4 An hydra based SST. Current status PDR. V-grooves 8 Planck L2 operations 7 Planck

BDT - 16-17 sept 200823

Concept 2 : why is it difficult to estimate the cost ?

• Performance is not achieved in the lab• The payload is not well defined• Technology is not clearly identified for several

key-systems• Existing technology should be improved• No space experience for several items• No such complex systems have already been

designed and launchedNeed for R&D to refine the concept, and O and A

phase studies to define the mission