Blue Dot Team « Multi aperture imaging »

BDT sept MAI techniques High accuracy visibility measurement Differential interferometry Nulling interferometry Hypertelecopes and pupil densification

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

BDT sept 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 sept Nulling interferometry : requirements Hot Jupiter Ocean planet Real Earth Real Jupiter Uranus Distance to the star (mas) Baseline (m) Total flux (mJy) e-4 1 e e-3 3 e-5 1 e-5 1 e-4 5 e e-5 3 e-5 5 e e-7 2 e-8 Contrast star/planet e+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

BDT sept 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 sept Nulling interferometry : several concepts Angel et al Mennesson et al. 1997

BDT sept 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.

BDT sept 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 sept « Scientific products of nulling interferometry (After Mennesson et Mariotti 1997) « Imaging »Spectral analysis

BDT sept Nulling interferometry in the lab (and in the world)

BDT sept 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 sept Stability of the null ddm N + - t t N2N2 N3N3 N1N1 N

BDT sept Nulling interferometry : requirements Hot Jupiter Ocean planet Real Earth Real Jupiter Uranus Distance to the star (mas) Baseline (m) Total flux (mJy) e-4 1 e e-3 3 e-5 1 e-5 1 e-4 5 e e-5 3 e-5 5 e e-7 2 e-8 Contrast star/planet e+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

BDT sept types of concepts Preparatory science concept : hot jupiters, brown dwarfs, exo-zodi characterisation –2 telescope array, Contrast 10 -4, near IR, stability no internal modulation = state of the art nulling performance Characteristation of exo Earths –Multiple telescope arrray, internal modulation, Contrast 10 -6, Thermal IR, stability Only concept 1 has been studied from ground and space using space agencies standards

BDT sept Missions requirements CharacteristicsPrep Sci. ConceptChar. Of Earth concept Spectral bandNear IRThermal IR Cophasing accuracy (residual opd) 2.5 nm rms3 nm rms Interferometric extinction Nulling stability Dephasing accuracy rad10 -3 rad Baseline m m Satellite guidingA few arcsec Fine guiding20 mas8 mas Telescope size30-40 cm1-3 m Instrument T100 K40 K Detector T55 K +/- 1K10 K

BDT sept Concept 1 : From the ground : GENIE and ALADDIN Need fr a quiet site : Antartica (ALADDIN) vs Paranal (GENIE). Absil et al 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 sept Concept 1 : from space : PEGASE mission concept

BDT sept 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 µm resolution on the sky 30 mas pupil plane 2 beam compressor D 1 Fringe sensor –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

BDT sept 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 -

BDT sept 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 sept 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 sept 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