ARENA Telescope and Instrument Robotization at Dome C Tenerife, Spain, 27/03/2007

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1 FOURMI a Large 4 m Interferometer for High Resolution Solar Physics and Extreme Coronagraphy at Dome C Luc Damé Service d'aéronomie du CNRS & LESIA Meudon Observatory, France Jean-Philippe Amans & Slimane Bensammar GEPI, Observatoire de Paris, France Jean Arnaud & Marianne Faurobert LUAN, Université de Nice, France Felix Bettonvil & Robert Hammerschlag Sterrekundig Instituut, Utrecht University, The Netherlands André Preumont Active Structures Laboratory, Université Libre de Bruxelles, Belgium ARENA Telescope and Instrument Robotization at Dome C Tenerife, Spain, 27/03/2007

2 Rationale: Facts, Objectives & Context The current FOURMI proposal is the results of one fact: Chromosphere, Transition zone & Corona: Require spectroscopy and imaging at very high spatial and temporal resolution of the Chromosphere-Corona interface New means (HINODE, STEREO) do not improve in UV-FUV spectroscopy (fast spectro-imaging), direct magnetic field measurement in corona and coronagraphy of the recommendations made for the future infrastructures of Europe (FP6 ASTRONET): 4 m class optical facility on ground FUV m class diffraction limited facility in space of the concomitant AO of ESA for Cosmic Vision released end of February (LoI 29 March: HIRISE Mission proposal with a 3 telescopes cophased interferometer for the FUV)

3 Future Missions/Facilities Needs Doppler information Temperature coverage, Discrimination Direct mag field measurement Resolution, resolution 3D view Fast spectral imaging Very high spatial, spectral & temporal resolutions (McAteer et al., 2003)

4 FP6 ASTRONET Recommendations for Required Solar Physics Facilities Transition Chromosphere- Corona: FUV thin lines at high spatial, spectral and temporal resolutions Meter Class Diffraction Limited FUV Mission, EUV X-ray complemented Continuous observations by Polar Sun-synchronous Near-Earth Orbit (telemetry advantage for dynamical studies: 40 Mb/s) MHD in photosphere and chromosphere with spectropolarimetry and 2D high temporal spectral and spatial resolutions 4 meter class facility with Diffraction Limited capabilities AO + interferometry: mass, dimensions, heat control, optics size and alignment advantages ASTRONET Poitiers, January 2007

5 Towards Very High Resolution 1 m UV Interferometer: 0.02" An INTERFEROMETER rather than a large telescope: Reduced height & mass small platform & launcher Fine Pointing and thermal aspects simplified by small telescopes (use of SiC) No need for the complex control of a large primary Phasing and pointing the "Perfect" Telescope 1.5 m

6 HIRISE/SOLARNET is a Unique Concept of Direct Interferometric Imaging on Extended FOV Compact Configuration: 3 telescopes of Ø350mm on 1m Spatial Resolution of (20 30km on the Sun in the UV) Multi-wavelengths spectral imaging nm with a subtractive double monochromator FUV & UV, coupled to an IFTS 0.002nm

7 3 x 3 Telescopes on Ground: 4 m Class Telescope Possible with 3T binding blocks Optically equivalent to 1 m FUV With small Ø70 cm telescopes, this 9-telescopes configuration provides an equivalent telescope > Ø4m diameter Recombination of the telescopes by active optics (interferometry) Perfect wavefront at individual telescope level by simple 64 elements Adaptive Optics (properly sized for 7 8 cm isoplanatic coherence patch)

8 Seeing & Dome C 60 m 30 m Excellent seeing expected abobe 30 m: 0.5" Superb seeing above 60 m: 0.2"

9 Seeing as function of time Good seeing when surface layer temperature gradient vanishes Temp. Gradient (6 /100m) No temp. gradient (Aristidi et al., A&A 2005) Seeing below 0.5" almost every day at tea time during ~3h

10 Comparison with other sites: excellent in most respects Site Paranal La Silla Maidanak South Pole Seeing Isoplan. angle Dome C (summer)

11 FOURMI Preliminary Design: Telescope & Interferometer Sizes Rationale Phasing individual telescopes (AO) allows to cophase them to gain a factor 10 from 0.5" to 0.05" Perfect AO: limit of 70 cm to 1 m for elementary telescopes On-axis initial triplet design and stiff telescope support plate of the 9 telescopes (cophased by triplets) made of 2 triangles with telescopes at the crossing points

12 Interferometer in Equatorial Mount La Palma & Dome C 2 versions are studied. One is more accurate and better adapted to the La Palma latitude of 29 (left, cradle) and the other to Dome C (right, fork) since the 75 latitude and excursions limited to ± 30 Both are open frame tower, open structure and open telescope

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14 Coronagraphic Sky: using it The nm Fe XIII line allows the measurement of the coronal magnetic field (Zeeman-Hanlé effects) very near from the limb if the pupil is clean (also Mg VIII m & Si IX m) Pupil is accessible (M3) for polarization analysis before adaptive mirror which, for few elements, do not require beam reduction 700 mm -> 50 mm (size of CILAS elements mirrors) Off-axis design allow full pupil access for apodization, low scattering and optimized adaptive optics

15 From Space to(and) Ground: off-axis Early coronal telescope envisaged for Dome C. 2 m off-axis but not optimized for mirror gradients, thermal load, structure stiffness. Some similarities of Space (UV) with Dome C Heat and cooling are of concern at Dome C like in Space (deep space radiators at -80 ) Solar load on primary and secondary is of concern (Gregory for tertiary filtering) Contamination, as ice, will form (if mirror is the coldest surface) > +3-5 heating of SiC allowing gradient control and focusing (SiC is highly conductive)

16 A Clean Pupil 0ff-axis Design

17 Solar Physics Facility at DOME C A coherent project for a Solar Physics facility involves addressing several matching issues for a successful high resolution extreme inner corona solar facility Tower precision and control compatible with bandpass of the mount and support structure Then the telescope needs structural stability compatible with the focus and thermal control Pointing is hopefully possible on reflection from tertiary or from guide telescope Wavefront control rapid enough for seeing and residual errors (also third order fixed corrections) Active control of the phase for "perfect" system

18 FOURMI DOME C Further Requirements First Principle of any instrumental realization: when something can be done directly in hardware don't do it by software: An open frame tower to get over the major turbulent ground layer with appropriate damping and control An open telescope(s) structure to limit telescope and mirror seeing An AO system to phase the elementary telescope pupil A cophasing system to phase a triplet of telescopes The same cophasing system for the triplet of triplets

19 TOWER: the DOT Open Frame Paradigm An open frame tower is studied both for a 4 m facility in temperate region (La Palma: 20 m) and Dome C (30 m). Slow wind on tower is sufficient for cooling Tower stiffness require damping and frequency control ("elastics" between booms and bars to shift frequency on DOT)

20 DOT from 15 to 30 m Tower

21 "Hammerschlag" Concept 30 to 60 m

22 The "Amans' Tabouret" Tower Platform is contained in the structure and, so, can be lifted with the "light" interferometric telescope and "bolted up" Hexagonal platform for the 4 m telescope is 12 m, tubes (stainless steel or carbon composite) are 70 cm and junction "balls" 1 m in diameter Shown here is the "La Palma" 20 m "Tabouret" (stool)

23 "Amans' Tabouret" Tower La Palma 20 m Dome C 30 m

24 Conclusion A high resolution imaging and spectroscopy facility, 4 meter class, addressing photosphere, chromosphere, transition zone and low corona, is possible at DOME C and benefits from the coronal sky condition, continuity of summer observations, clean IR access and excellent seeing (0.5 arcsec). To address 2D spectro-imaging, spectropolarimetry and direct magnetic field measurement lower in the atmosphere, convectionphotosphere-chromosphere magnetic link, a 4 m class HR facility is required and a mass/size/cost effective approach suggests small SiC telescopes + perfect A0 + interferometry This High Resolution Coronal Facility, FOURMI, is the way to go and is proposed as a desirable possibility for FP7 Design Studies of the 4 m class facility on ground

25 Thank you!