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Understanding ESA's DARWIN Space Interferometer: Technology and Science for Exo-Earth Detection

The ESA's DARWIN space interferometer program, proposed to identify and characterize exo-Earths, utilizes a hexagonal configuration of telescopes operating in the infrared spectrum (5-20 microns) and employs nulling interferometry to separate weak planetary signals from their bright parent stars. The project has undergone significant technological advancements since its initial proposal in 1993, including successful tech demonstrations. DARWIN aims to provide high-resolution imaging of exoplanet atmospheres, looking for potential biosignatures and insights into astrophysical phenomena.

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Understanding ESA's DARWIN Space Interferometer: Technology and Science for Exo-Earth Detection

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  1. ESA’s Darwin space interferometer Huub Röttgering Sterrewacht Leiden

  2. The InfraRed Space InterferometerDARWIN • 2014 • 6 1.5 m telescopes • Hexagonal configuration • Beam combiner • Passive cooling (40 K): 5-20 micron

  3. Overview • Introduction • Timeline / status project • Relation with NASA’s Terrestrial Planet Finder • Imaging considerations • Science

  4. Science • Finding and characterising exo-Earth’s • Nulling interferometry

  5. The Problem Detecting light from planets beyond solar system is hard: Planet emits few photons/sec/m2 at 10 mm Parent star emits 106 more Planet within 1 AU of star Dust in target solar system 300 brighter than planet Finding a firefly next to a searchlight on a foggy night

  6. Science • Finding and characterising exo-Earth’s • Nulling interferometry • Atmosphere -> CO2 • Wet and pleasant H20 • Life O3 (? / !) • High resolution and sensitive IR imaging • Cophasing using an off-axis reference star Earth at 10pc

  7. Darwin timeline • 1993: Léger et al • ``Darwin proposal’’ • 2000 Presentation Alcatel system level study • 2004 Results significant technology development program (15 Meuro) • Optical components, coolers, thrusters, metrology, control software, 2 breadboards … • 2007 – SMART2 techno demonstration flight • (mainly LISA technology) • 2010 – SMART3 techno demonstration flight • 2-3 space craft • 2014 – launch

  8. NASA’s TPF • Similar goals and timelines 1999: IR interferometer with cooled 4x3.5 m mirrors and ~75-1000 m baseline

  9. Vegetation edge 2000 Blue sky Earth spectrum from Earth- shine

  10. SVS coronagraphe Variable-Pupil Coronagraph IR Nulling Interferometers M2 M1 M3 Hyper-telescope Large Aperture IR Coronagraph 2001: 4 different studies

  11. 2002: down selection for 2 concepts • Coronagraph – Difficult • 10-15 meter mirror with rms surface ~< 1 Å • Deformable mirrors - control to <1 Å rms over wide range of scales • Wavefront sensing - adequate for <1 Å control • Interferometer - Complex • Cryogenic nulling - 10-5 or 10-6 depth across ~1 octave • Wavefront & amplitude control - spatial filter in mid-IR (+ DM for low spatial freqs) + control of thermal & vibration effects + acc. amplitude measurement • Beam transport issues (rejection of stray light at small angles) Variable-Pupil Coronagraph IR Nulling Interferometers

  12. Joined ESA/NASA mission • MOU: aims for a joining in 2006 • Plan • Both sides continue technical studies • Regular scientific contact • Criteria to guide continuation after 2006 • #1: Sensitivity in finding and characterizing exoplanets • #2: Richness of astrophysical science opportunities • #3: Technology development needed • #4: Life-cycle costs • #5: Risk of cost, technology, schedule, on-orbit failures • #6: Reliability and robustness

  13. Astrophysical imaging with Darwin 1. Imaging considerations 2. Science Röttgering et al. 2003, Heidelberg conference

  14. Imaging performance at 10 micron • Sensitivity (Takajima and Matshura, 2001) • Limited by shot noise from the zodiacal background. • Similar to JWST • Point source sensitivity • 1 hour, s/n=5: 2.5 microJy • Image sensitivity • S_integrate/noise > 50 within FOV • > 2.5 microJy for a 100 hour • Resolution • Baselines up to 500 meter • 200 m baseline: 10 mas • JWST 350 mas

  15. Imaging considerations • PSF of an individual telescope: 1.4 arcsec • = maximum FOV for pupil combination • Mapsize (200 m baseline/telescope diameter) <~ 100 * 100 independent pixels • Complexity • per configuration maximum 6*5/2 = 15 uv points • number of uv-points >>~ number of image parameters • for a complex map of 100 * 100 independent pixels: • >>~ 666 configurations

  16. 16 Baseline dynamics Basic reconfiguration approach a single expansion up to baselines of 500 m and contraction coupled to a 60o rotation bang-bang thrust profile both radially and tangentially <dB/dt> = 1.5 cm/s @ 1 mN d’Arcio et al. 2001 Fastest reconfiguration cycle takes about 16 hours Snapshots will be taken “on the fly”

  17. 17 UV coverage • Hexagonal array -> 9 independent visibilities per snapshot • 600 snapshots, ~ 5400 uv points/reconfiguration cycle • -> Filling the UV plane is ’’easy’’ • Ground based telescopes are ``fixed’’ • (radio) Baseline/apertureis huge d’Arcio et al. 2001

  18. Issue: Cophasing • How to phase-up the array not using the target? • Essential to • integrate longer than the coherence time of the interferometer (~10 sec) • Measure complex visibilities (Amplitude and phase) needed for imaging • Off-axis bright stars (there are enough!) • Similar to PRIMA instrument for the VLTI (Quirrenbach, this meeting) • Multiplexing in wavelengths has the advantage that science and reference beams travel along common path (Alcatel) • Implementation • Modification to the nulling beamcombiner (Alcatel) • Separate imaging beamcombiner

  19. How to get a large Field of View? • Mosaicing • Expensive in time • homothetic mapping • Relative complex • Pupil matching in magnification and orientation before image plane combining • Implementation • Pupil matching/zooming optics at central beamcombiner • Pupil matching/zooming at telescopes (see d’Arcio and le Poole, 2003)

  20. Physical processes observable at 6-20 micron • Molecules: Rotational and vibrational lines • Temperatures, densities, kinematics, Chemistry • Ions: Forbidden fine-structure lines • Temperatures, densities, kinematics, abundance's • Dust: PAH features, continuum shape • Composition, temperature • Late type stars: continuum (high z) • Spatial scales ISO observations Starburst galaxy Circinus

  21. Appropriate sensitivity and angular resolution ? Star and planet formation AGN Distant galaxies

  22. Star and Planet formation • Sketch of scenario maybe in place (Shu et al. 87) • Vast range of conditions and relevant timescales • densities 10^4 - 10^13 /cm^3 • temperatures 10 - 10,000 K • month - 10^6 years • Issues • density, temperature and dynamical structure of disks? • At what stage and when do planets form?

  23. Compendium of Monnier and Millan-Gabet of K-band sizes of YSOs Disk models of D’Alessio, Merin

  24. ISOCAM survey of your starclusters at 6.6 and 14.3 micron (Eiroa et al) An unphysical, unrealistic extrapolation -> fainter YSO are small (10-100 mas ?) 4 2 0 MIDI Log Radius[mas] Darwin -2 -1 0 Log flux @ 14 micron [Jy]

  25. Active galactic Nuclei • Zoo: Seyfert, Starburst quasars ... • unification: orientation, time-evolution, mass, spin • 1000 times more AGN at z=2 than z=0 • Every galaxy has a central massive Blackhole (?) • Issues: • Physics? When and how do BH form? • Relation to Galaxy formation?

  26. Models of Tori of Granato et al. • AGN may contain dusty tori • can obscure the central QSO • feeds the massive Black Hole • Radiative transfer model of a dusty torus • size scales with QSO luminosity • SED from l = 1 - 300 mm • morphologies at l = 10 mm Adapted to NGC 1068, Heijligers etal.

  27. Darwin observations of Tori • D = 300 times the sublimation radius • NGC1068: • Bight, low luminosity nearby AGN • ~10 Jy: prime target for MIDI/VLTI in 2003 • 1.7 1031 erg/s/Hz at l = 10 mm • (prime target for MIDI/VLTI in 2003) • Weak AGN observable up to z = 1 - 2 • Stronger AGN up to z = 10 1’’ Ln (10 m m [1030 erg/s/Hz] 0.1’’ NGC1068 50 m Jy 5 m Jy 0.01’’ 0.01 0.1 1 10 redshift

  28. Distant Galaxies • When and how do galaxies form? • Star formation history, galaxies shapes • Relation to black hole formation • 8-10 meter telescopes: a few thousand with 3<z<6 and still counting • Hardly morphological information • Darwin: morphologies of the older stellar component • observe 2 micron rest == 10 micron for z=4 • Semi-analytical models of galaxy formation as guidance • input: evolution of cold-dark matter halos, prescriptions for cooling, star formation and feedback, dust… • output: large samples of mock galaxies and their properties (SF, mass, type)

  29. FIRES survey • IsaacVLT • : 2.5^2 arcmin • 96 h in J, H, K HDFS • limit in K = 24.4 mag • Image HST I+H+K • Franx, Labbe, Forster,schreiber, Rix, Rudnick, Röttgering, etal.

  30. SED fitting • with galaxy templates • Photometric redshift • Estimate 10 micron flux density • Rudnick, Labbe et al.

  31. JWST resolution At 10 micron (0.35 arcsec)

  32. Fn (10 m m ) m Jy 100 hour, S_int/noise=50 100 hour Pointsource S/N=5 (photometric) redshift

  33. Conclusion • Darwin will be a powerful instrument for • Finding and characterizing exo-Earth • Astrophysical studies • Sensitivity is similar to JWST • Cophasing is an important issue • Size scales, AGN, YSOs, distant galaxies are appropriate • Case for larger fields

  34. 2025 Terrestrial planet imager? 20 8-m telescopes

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