1 / 23

Blue Dot Team

Blue Dot Team. « Multi aperture imaging ». MAI techniques. High accuracy visibility measurement Differential interferometry Nulling interferometry Hypertelecopes and pupil densification. Star. Planet. q. D.sin q. D. T1. T2. + p. Beam combiner. 1 arcsec.

rigg
Download Presentation

Blue Dot Team

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related