1. Blue Dot Team « Multi aperture imaging »

2. BDT - 16-17 sept 2008 2 MAI techniques High accuracy visibility measurement Differential interferometry Nulling interferometry Hypertelecopes and pupil densification

3. BDT - 16-17 sept 2008 3 Nulling interferometry : principles Beam combiner T2T1 D D.sin   StarPlanet ++ 1 arcsec =10  m, D=10m,  =0.1 arcsec

4. BDT - 16-17 sept 2008 4 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

5. BDT - 16-17 sept 2008 5 Nulling interferometry : requirements Hot Jupiter Ocean planet Real Earth Real Jupiter Uranus Distance to the star (mas) 5100 5202000 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+6 1 e+9 1e +7 6 e+8 4 e+7 7 e+10 Planets around a G0 Star at 10 pc V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands

6. BDT - 16-17 sept 2008 6 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

7. BDT - 16-17 sept 2008 7 Nulling interferometry : several concepts Angel et al. 1989 Mennesson et al. 1997

8. BDT - 16-17 sept 2008 8 Internal modulation (Mennesson et al. 2005)  /2   /2 Detector Sub-arraysTransmission map  4 transmission central 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.

9. BDT - 16-17 sept 2008 9 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.

10. BDT - 16-17 sept 2008 10 « Scientific products of nulling interferometry (After Mennesson et Mariotti 1997) « Imaging »Spectral analysis

11. BDT - 16-17 sept 2008 11 Nulling interferometry in the lab (and in the world)

12. BDT - 16-17 sept 2008 12 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).

13. BDT - 16-17 sept 2008 13 Stability of the null ddm N + - t t N2N2 N3N3 N1N1 N

14. BDT - 16-17 sept 2008 14 Nulling interferometry : requirements Hot Jupiter Ocean planet Real Earth Real Jupiter Uranus Distance to the star (mas) 5100 5202000 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+6 1 e+9 1e +7 6 e+8 4 e+7 7 e+10 Planets around a G0 Star at 10 pc V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands

15. BDT - 16-17 sept 2008 15 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

16. BDT - 16-17 sept 2008 16 Missions requirements CharacteristicsPrep Sci. ConceptChar. Of Earth concept Spectral bandNear IRThermal IR Cophasing accuracy (residual opd) 2.5 nm rms3 nm rms Interferometric extinction 10 -4 10 -6 Nulling stability10 -5 10 -9 Dephasing accuracy5 10 -3 rad10 -3 rad Baseline10-500 m20-500 m Satellite guidingA few arcsec Fine guiding20 mas8 mas Telescope size30-40 cm1-3 m Instrument T100 K40 K Detector T55 K +/- 1K10 K

17. BDT - 16-17 sept 2008 17 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)

18. BDT - 16-17 sept 2008 18 Concept 1 : from space : PEGASE mission concept

19. BDT - 16-17 sept 2008 19 MAIN FUNCTIONALITIES OF THE PAYLOAD Spectro detectors 55 K detection stage +fiber coupling (, 2.5 nm rms stability 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 sensor 1+2 0.6–1.0 µm 2 nm resolution I2I2 I1I1 combining stage  phase shift d ODL 1 1 cm stroke 1 nm resolut. ODL 2 Siderostat 1 O 1 D’ O1O1 Siderostat 2 O2O2 M1M1 O2O2 combiner pupil plane 1 beam compressor 1 G=D/d D

20. BDT - 16-17 sept 2008 20 SNR IN NULLING MODE (hot jupiters case) nulling instabilty due to : opd stab. :   nm rms flux balance stab. :   % rms (pointing stability) detector noise et  Td + RON optics thermal noise et  To photon noise integration time  i mi n ma x SNR minin [ min max ] parameters :  i =10h, D=30 cm,  o =0.1,  q =0.6, =55°K,  Td =0.1°K rms, =100°K,  To =1°K rms,  > < 0.01,   =2.5 nm rms,   =0.003 rms, RON 10e -

21. BDT - 16-17 sept 2008 21 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

22. BDT - 16-17 sept 2008 22 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)

23. BDT - 16-17 sept 2008 23 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 launched Need for R&D to refine the concept, and O and A phase studies to define the mission