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

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
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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
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GREGOR Cross Section
New, fully
retractable
dome
Telescope
tube and
mount
Wind shield,
retractable
External
mirror
elevator
Science foci
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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
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Critical Areas
• Internal seeing
• Track ambient temperature!
• Wind buffeting
• Increase resonance frequency
• Contamination
• Use windshields above design
windspeed
• Cleaning procedure
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– athermal structure
– thermally controlled primary
mirror
– thermally controlled heat trap at
primary focus
– evacuated coudé path*
– lightweight optics
– lightweight structure
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Optical Design
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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
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Optics Highlights
• Use C/SiC technology for first three mirrors
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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
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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
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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)
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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)
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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
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100 (TBD)
150 Hz
<  / 10
5 arcsec
1 arcsec
15 µm ptv
Visible
 0.5 %
< 10 % (< 50 %)
5 yrs
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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
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GREGOR Infrastructure
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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
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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
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