1. Spectral Analysis of atmospheres by nulling interferometry Marc OLLIVIER Institut d’Astrophysique Spatiale - Orsay

2. Nulling interferometry : principles Molecules 2008 - 21 nov 2008 - M.O.2 Beam combiner T2T1 D D.sin   StarPlanet ++ 1 arcsec =10  m, D=10m,  =0.1 arcsec

3. Nulling interferometry : key-issues : perfect matching of the wavefronts 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 Molecules 2008 - 21 nov 2008 - M.O.3

4. Planetary observations : requirements Planets around a G0 star at 10 pc V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands Molecules 2008 - 21 nov 2008 - M.O.4 Hot Jupiter Super planet Real Earth Real Jupiter Uranus Distance to the star (mas) 5100 5202000 Telescope diameter (m) 20 150 400 1 7 20 1 7 20 0.2 1.4 4 0.05 0.4 1 Planetary 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

5. A few interesting photons, a lot of noise Molecules 2008 - 21 nov 2008 - M.O.5  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

6. Several configurations Molecules 2008 - 21 nov 2008 - M.O.6 Angel et al. 1989 Mennesson et al. 1997

7. Internal modulation (Mennesson et al.) Molecules 2008 - 21 nov 2008 - M.O.7 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. - Inherent modulation (Absil)  /2   /2 Detector Illustration : courtesy O. Absil

8. What is observed ? Single pixel detector 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, instrumental noise, detection noise) Image reconstruction software necessary to get F(α,δ,λ) using multi baseline / λ information (Thiébaut et al.) Molecules 2008 - 21 nov 2008 - M.O.8

9. Scientific products of nulling interferometry Molecules 2008 - 21 nov 2008 - M.O.9 (After Mennesson et Mariotti 1997) « Imaging »Spectral analysis

10. Nulling interferometry in the lab Molecules 2008 - 21 nov 2008 - M.O.10 Booth, Martin and Loya, 2008 JPL’s PDT facility

11. Nulling interferometry in the lab Molecules 2008 - 21 nov 2008 - M.O.11 Chazelas, 2006

12. Stability of the null 1/F noise Need for control loops to stabilize the null Control loop based on the interferometric signal instead of metrology signal (to avoid differential effects) Molecules 2008 - 21 nov 2008 - M.O.12

13. IAS test bench : synapse Molecules 2008 - 21 nov 2008 - M.O.13

14. Stability of the null (Gabor et al;) Molecules 2008 - 21 nov 2008 - M.O.14 ddm N + - t t N2N2 N3N3 N1N1 N

15. Toward a space mission ? Molecules 2008 - 21 nov 2008 - M.O.15

16. Planetary observations : requirements Planets around a G0 star at 10 pc V (0.55μm) / L (3.5μm) / N (10.2 μm) Bands Molecules 2008 - 21 nov 2008 - M.O.16 Hot Jupiter Super 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

17. 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 (In Europe) Only concept 1 has been completely studied using space agencies standards Molecules 2008 - 21 nov 2008 - M.O.17

18. Mission requirements Molecules 2008 - 21 nov 2008 - M.O.18 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

19. Preparatory science from space Molecules 2008 - 21 nov 2008 - M.O.19

20. Main funtionalities of the payload Molecules 2008 - 21 nov 2008 - M.O.20 BDT - 16-17 sept 2008 20 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. Siderostat 1 O 1 D’ O1O1 Siderostat 2 O2O2 M1M1 O2O2 combiner pupil plane 1 beam compressor 1 G=D/d D

21. SNR in nulling mode Molecules 2008 - 21 nov 2008 - M.O.21 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 -

22. Payload composition Beam transportation Fine Relative Angle Sensor + actuator Optical delay line Achromatic phase shifter Optical filtering stage Beam combining stage Detection stage Molecules 2008 - 21 nov 2008 - M.O.22

23. 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) Molecules 2008 - 21 nov 2008 - M.O.23 BDT - 16-17 sept 2008

24. Preparatory mission and ESA Cosmic Vision process Science poorly considered Feasability estimated as highly risky Cost to high Part of the scientific information provided by other technics Project not selected Molecules 2008 - 21 nov 2008 - M.O.24

25. Characterisation of exo-Earths : why is it difficult to design a mission and to estimate the cost ? Targets are not yet identified (size, distance, central star, zodi level…) Required performance is not well defined Estimated performance is not yet achieved in the lab The payload is not well define 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 O and A phase studies to define the mission and identify the required technology Molecules 2008 - 21 nov 2008 - M.O.25

26. Conclusion The simpliest nulling interferometry mission is already a big (huge) space mission The ratio science/cost of a precursor (preparatory science) is considered as very low However, the mission concept (payload + system + operations) should be demonstrated A mission to analyse earthlike planets cannot be considered is present (future ?) plans of (European) Space Agency Molecules 2008 - 21 nov 2008 - M.O.26

27. « The end justifies the means » phylosophy When everything appears hopeless call the « A-team » building of a new international structure such as in particle physics domain (LHC and Higgs boson question) with fundings adapted to big projects ? Molecules 2008 - 21 nov 2008 - M.O.27