Blue Dot Team

1. Blue Dot Team « Multi aperture imaging »

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

3. Star Planet q D.sinq D T1 T2 +p Beam combiner 1 arcsec l=10mm, D=10m, q=0.1 arcsec Nulling interferometry : principles 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 BDT - 16-17 sept 2008

5. Nulling interferometry : requirements • Planets around a G0 Star at 10 pc • V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands 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) ~ 10 to 100 x Signal IR background (locl zodi + instrument emission ~ 1000 x Signal Exo-zodi (global emission x interferometre response) ~ 300 x Signal BDT - 16-17 sept 2008

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

8. Detector p/2 -p/2 Detector Internal modulation (Mennesson et al. 2005) transmission central symmetry conjugaison Sub-arrays Transmission map 4 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 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. BDT - 16-17 sept 2008

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

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

13. N + ddm - t N   N2 N1 N3 ddm t Stability of the null BDT - 16-17 sept 2008

14. Nulling interferometry : requirements • Planets around a G0 Star at 10 pc • V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands 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 BDT - 16-17 sept 2008

16. Missions requirements 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) BDT - 16-17 sept 2008

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

19. pupil plane 1 pupil plane 2 combiner beam compressor 1G=D/d D’ beam compressor D O 1 O2 O2 O1 M 1 Siderostat 2 Siderostat 1 d ODL 11 cm stroke1 nm resolut. ODL 2 Fringe sensor1+20.6–1.0 µm2 nm resolution FRAS 1+2 1.0-1.5 µmresolution on the sky 30 mas D 1 combining stage +p phase shift I1 I2 MAIN FUNCTIONALITIES OF THE PAYLOAD az2 2.5 nm rmsstability zone 55 Kdetection stage +fiber coupling (, optical head internal laser metrology Spectrodetectors BDT - 16-17 sept 2008

20. SNR IN NULLING MODE (hot jupiters case) detector noise <Td> et sTd + RON photon noiseintegration time ti nulling instabilty due to :opd stab. : sd nm rms flux balance stab. : se % rms(pointing stability) optics thermal noise<To> et sTo SNR min in [lminlmax] lmin lmax parameters : ti=10h, D=30 cm, ho=0.1, hq=0.6, <Td>=55°K, sTd=0.1°K rms, <To>=100°K, sTo=1°K rms, <2pd/l><510-3 rad, <e> < 0.01, sd=2.5 nm rms, se=0.003 rms, RON 10e- 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 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) 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 BDT - 16-17 sept 2008