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GREGOR Upgrade of the GCT on Teneriffe with a 1.5m Solar Telescope O. von der Lühe, W. Schmidt, D. Soltau (KIS, Freiburg) F. Kneer (USG, Göttingen) J. Staude (AIP, Potsdam) Motivation German ground based solar science needs access to large solar facilities to stay competitive A modern 1.5 m solar telescope opens new scientific opportunities The 35 years old Gregory Coudé Telescope has outlived its scientific life Izaña is a developed observatory with established administrative procedures A step towards an international facility of the 3-4m class is necessary to validate enabling technologies: Adaptive optics Lightweight optics and structures Thermal control 24 May 2017 GREGOR 2 GREGOR Main Characteristics 1.5 m diameter, direct pointing, Gregorian Telescope with centered tertiary (LEST inheritance) Open Telescope tube, fully retractable dome (DOT inheritance) Alt-Az mount Lightweighted optomechanical structure Integrated adaptive optics system Focus redirectable to two laboratories FOV 300 arcsec, feff 75 m Low instrumental polarization NIR and TIR* capability Dead-reckoning pointing & tracking 24 May 2017 GREGOR 3 GREGOR Cross Section New, fully retractable dome Telescope tube and mount Wind shield, retractable External mirror elevator Science foci 24 May 2017 GREGOR 4 Tradeoffs Evacuated / He-filled telescope + internal seeing (vacuum, He-filling) -- internal seeing (closed dome) + contamination protection -- wind protection (closed dome during operation) - weight (must withstand vacuum) - window Open Telescope - internal seeing (open telescope) ++ internal seeing (retracted dome) - dust protection - wind protection ++ weight (can be lightweighted) ++ no window 24 May 2017 GREGOR 5 Critical Areas • Internal seeing • Track ambient temperature! • Wind buffeting • Increase resonance frequency • Contamination • Use windshields above design windspeed • Cleaning procedure 24 May 2017 – athermal structure – thermally controlled primary mirror – thermally controlled heat trap at primary focus – evacuated coudé path* – lightweight optics – lightweight structure GREGOR 6 Optical Design 24 May 2017 Triple Gregorian optics f/1.75, 1.5 m primary 300 arcsec field stop at F1 Polarimetric calibration optics at F2 Field lens near F2 to place 110 mm pupil near M6 and M7* Fast guiding / DM can be placed at M6 and M7 F/50 tertiary focus can be placed in two labs Feff = 75 m GREGOR 7 Optics Highlights • Use C/SiC technology for first three mirrors – – – – – – – – 24 May 2017 lightweighted primary weight ~150 kg high CTC - uniform temperature active mirror cooling to dispose of 170 W absorbed sunlight air flushing or cold plate for TC surface figuring considered most critical item six DOF precision control of M1/M2 alignment M3 used for focussing GREGOR 8 Solar Lite M1 development at DSS Two halves of Solar Lite 1m main mirror greenfelt bodies during joining and prior to infiltration. Pictures courtesy Dornier Satteliten Systeme 24 May 2017 GREGOR 9 Adaptive Optics I Major enabling technology item Critical for combining high spatial with high spectral resolution at sufficient sensitivity Integrated into telescope (M6/M7) Serves all foci Major development item Development of AO for VTT Simultaneous compensated and uncompensated image taken with the NSO / Sac Peak Solar Adaptive Optics System (Rimmele, 1999) 24 May 2017 GREGOR 10 Adaptive Optics Requirements Analysis • High Level Goal: Strehl > 0.5 for more than 50% of the time. Feasible only with 256 DOF and fc > 200 Hz. • Reasonable "first start" system: 64 DOF and fc > 150 Hz achieves Strehl > 0.5 for 20% of the time and Strehl of 0.25 for 50% of the time. Should be doable with today's technology. • 66 DOF: Zernike polynomials n = 10 ( ~100 actuators) • 256 DOF means all Zernike polynomials up to n = 22 ( ~400 actuators) 24 May 2017 GREGOR 11 AO Top Level Requirements No. of degrees of freedom No. of channels for Dm / WFS Closed loop bandwidth Overall residual WFE due to system at tertiary focus Tip-Tilt compensation range: < 5 Hz 5 Hz ... 100 Hz Deformable mirror deformation range, overall Wavelength range for WF Sensor Intensity contrast of target structure Fraction of sunlight used for WFS Lifetime 24 May 2017 GREGOR 66 100 (TBD) 150 Hz < / 10 5 arcsec 1 arcsec 15 µm ptv Visible 0.5 % < 10 % (< 50 %) 5 yrs 12 GREGOR Instrumentation • Filtergraph – Redeployment of Göttingen FPI from VTT – Installation in main observing room • UV-Spectro-Polarimeter – Redeployment of Freiburg POLIS from VTT – Installation in main observing room • General Purpose Grating Spectrometer – Refurbishment of present Czerny-Truner spectrpgraph of GCT – Installation in spectrograph room • Instrument Control from separate room 24 May 2017 GREGOR 13 GREGOR Infrastructure • • • • • • Removal of old dome and elevator hut Erection of new, fully retractable dome Erection of removable windshield system Increase of inner tower height Installation of new external elevator Installation of new control room in living quarters 24 May 2017 GREGOR 14 Programmatics • Realisation as a German Project – established, lean structure already in place (DFG, KIS & partners) – collaboration with German industry • International participation TBD – stepping stone for further participation in large international projects – dissemination of experience gained to interested partenrs – moral support and advice welcome • Exploitation through existing procedures – CCI International Time – collaborations with partner institutes 24 May 2017 GREGOR 15