GREGOR Upgrade of the GCT on Teneriffe with a 1.5m Solar Telescope

1. GREGORUpgrade 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)

2. Motivation • German ground based solar science needs access to a new large solar facility of the 3m class to stay competitive (LEST, AST) • A step „in between“ is widely regarded as necessary to validate enabling technology (adaptive optics) • A modern 1.5 m solar telescope opens new scientific opportunities • The 45 cm Gregory Coudé Telescope is 35 years old, has lived its scientific life • Izaña is a developed observatory with established administrative procedures GREGOR

3. 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 GREGOR

4. GREGOR Cross Section New, fully retractable dome Telescope tube and mount Wind shield, retractable External mirror elevator Science foci GREGOR

5. 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 GREGOR

6. Internal seeing Wind buffeting Contamination Track ambient temperature! athermal structure thermally controlled primary mirror thermally controlled heat trap at primary focus evacuated coudé path* Increase resonance frequency lightweight optics lightweight structure Use windshields above design windspeed Cleaning procedure Critical Areas GREGOR

7. Optical Design • 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

8. Optics Highlights • Use C/SiC technology for first three mirrors • 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

9. 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 GREGOR

10. 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) GREGOR

11. Adaptive Optics II GREGOR

12. 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) GREGOR

13. AO Top Level Requirements GREGOR

14. GREGOR Instrumentation • Acommodation at two levels • main observing room • spectrograph room • plenty of space • Redeployment from VTT • Göttingen FPI Filtergraph • POLIS • New IR instruments GREGOR

15. 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 GREGOR

16. Programmatics • Realisation as a purely German Project • established, lean structure already in place (DFG, KIS & partners) • easier to sell to funding bodies • collaboration with German industry • International participation TBD • moral support and advice welcome • dissemination of experience gained • Exploitation through existing procedures • CCI IT • collaborations GREGOR

17. Planning & Schedule I • Done: • Major concept tradeoffs • Top level design studies (Telescope, AO) • M1 design study (Dornier) • Under way: • Science & Financial Plans, Proposal preparation • Engineering study of Telescope • Realization of M3 to study surface technologies • Subsystem studies GREGOR

18. Planning & Schedule II • Preparatory phase to continue until End `99 • Detailed Design Phase (2000 - mid 2001) • detailed designs of Telescope optics, optomechanics, control by Industry • designs of focal instruments by Institutes • civil engineering design • adaptive optics at VTT • Construction Phase (mid `01 - mid `03) • construction / AIV of telescope • construction of AO system • civil engineering works • erection of dome and telescope • Verification and Tests (mid `03 - early `04) • Integration of FP instruments • system level tests GREGOR

19. Financing • Total cost estimated to 7.2 MDM (± 20%) • Thorough industrial cost assessment pending • About 40% from operational budgets of Partner institutes • Remaining funds through third party proposals • Proposal by end of year GREGOR