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Optical performance of LAMOST telescope

Optical performance of LAMOST telescope. Xiangqun Cui National Astronomical Observatories / Nanjing Institute of Astronomical Optics and Technology, CAS. General introduction Completion of telescope engineering Optical system and performance The contribution in development of active optic

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Optical performance of LAMOST telescope

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  1. Optical performance of LAMOST telescope Xiangqun Cui National Astronomical Observatories / Nanjing Institute of Astronomical Optics and Technology, CAS

  2. General introduction • Completion of telescope engineering • Optical system and performance • The contribution in development of active optic • Prospect

  3. General introduction

  4. Large scale spectroscopic survey requires wide field of view and large aperture telescope

  5. Comments by Dr. Ray Wilson - Telescope optics expert and inventor of active optics ... Extension of the Schmidt telescope to bigger diameters could then only be achieved by replacing refrecting corrector to reflecting correcotr. But no one had dared to attempt such a difficult technical project until the Chinese optical experts of Nanjing Observatory proposed the LAMOST project, published by Wang et al. in 1996. Twelve years lalter, we are now celebrating on 16th October 2008 the completion of this extremely difficult project. Its success from the preliminary tests seems already assured and represents a triumph for the director of the project, Mrs Xiangqun Cui, who already did great work during her earlier stay at ESO in Garching (Germany). Not only does this project use a reflecting corrector, but it also uses a fixed mounting between corrector and spherical mirror involving a coelostat feed into uses a rotating corrector. Futhermore, both corrector and mirror are segmented. Thus the LAMOST concept embodies every aspect of the most advanced modern telescope technology. …  ...Extension of the Schmidt telescope to bigger diameters could then only be achieved by replacing refracting corrector to reflecting corrector. But no one had dared to attempt such a difficult technical project until the Chinese optical experts of Nanjing Observatory proposed the LAMOST project, …

  6. LAMOST overview

  7. Characteristics of LAMOST • A meridian active reflecting Schmidt telescope with an active correcting plate —Wang-Su reflecting Schmidt telescope • With both wide field of view and large aperture. • 4000 optical fibers for spectroscopy with highest spectrum acquiring rate.

  8. FOV Aperture of Telescopes

  9. Completion of telescope engineering

  10. Schedule • Proposal reviewed Nov. 1996 approved Apr. 1997 • Feasibility Study Aug. 1997 • Preliminary Design Jun. 1999 • Detailed Design Sep. 2001 • Construction 2001-2008 • First light Sep. 2008 • Inauguration Oct. 2008 • CAS acceptance Dec. 2008 • Government acceptance June 2009

  11. October 16, 2008LAMOST on the inauguration ceremony

  12. LAMOST- a complex system • 61hexagonal sub-mirrors with 1.1m in diagonal • 61 active mirror support cells • 2 axes alt-az mounting with 8mplatform • 5 dimensions focal moving mechanism • 6mand 7mmirror support structures • 9084motors • 4000 optical fibers（130km) • 4000 fiber positioning units • 16 spectrographs • 324kx4k CCDcameras • 251 computors • 800,000 lines software

  13. LAMOST- an economic telescope design concept for extremely large telescope • All mirrors are spherical or plano (aspherical surface created by active optics) • Most parts are integrated with same units • With huge amount of data will be obtained, its scientific output with lowest cost

  14. Key technologies Active optics Positioning of 4000 optical fibers Fabrication of large hexagonal thin mirrors Support technology for large thin deformable segmented mirrors Mounting and tracking for large telescope Multi objects fiber spectrographs Dome seeing of 40m long optical path Data procession

  15. 24 sub-mirrors of MA

  16. Fabrication for MA sub-mirrors • Finish in Oct 2006 surface accuracy： All RMS ≤18nm RMSaverage< 12.5nm

  17. MB with 37 sub mirrors

  18. Test results for MB Surface accuracy： RMS： 8.2nm-16.1nm PV： 68.3nm-144.9nm

  19. Focal tracking mechanism and 4000 optical fibers

  20. 4000 fiber positioning Positioning unit with 2 step motors Focal Plate for holding 4000 fibers Double arm scheme

  21. 4000 fiber positioning units

  22. 单元个数 单元重复定位精度标准偏差（微米） Repeatability (in micron)

  23. 16 Low/MediumResolution Spectrographs First spectrograph for LAMOST in NIAOT RL = 1000/2000 RM= 5000/10000 Spectral range: Low blue: 370—590nm red: 570—900nm Medium blue: 510nm — 540nm red: 830nm — 890nm 2x 4096×4096CCD

  24. LAMOST-spectrographs

  25. Efficiency of spectrograph 370~900nm • Target ：35%（peak） • According to test on reach parts: 50% • According to test on whole spectrograph: 43%

  26. 32 CCD Detectors E2V / England Chinese Company CCD: 4096X4136 pixel , red and blue - In 200K/S fast readout speed, 40s for each frame, noise < 4 electrons； - In 50K/S slow readout speed, 170s for each frame, noise < 3 electrons.

  27. Spectra of stars （04/2009） over 3600 spectra obtained in one observation (>97%) Spectrograph #5 Spectrograph #4

  28. Oct. 26, 2009 M31

  29. The completion of LAMOST at Xinglong shows that the technical challenges especially the active optics and optical fiber positioning system have been successfully overcome and telescope technologies have been developed and step forwarded dramatically in China

  30. Optical system and performance

  31. Optical System

  32. Ma: reflecting corrector (24 sub-mirrors) ~ 5.72mX4.4m • Mb: spherical mirror (37 sub-mirrors) ~ 6.67mX6.05m

  33. Characteristics of LAMOST optical system • The optical axis is ingeniously fixed in the meridian plane and the reflecting Schmidt corrector tracks the motion of celestial objects • Realize large aperture of the reflecting Schmidt telescope by active optics • No blind area for LAMOST • The curvature center of the primary mirror MB is located in the optical system • The deformation of the structure caused by the change of gravity is very small • The size and shape of the aperture is variable

  34. Image quality (including atmospheric refraction） EE80 (in arcs)

  35. Aperture of LAMOST

  36. Vignetting

  37. Possible tracking time

  38. Test result by Shack-Hartmann • Two main Shack-Hartmann wave front sensors : • Located at the curvature center of the primary mirror MB for test the quality of co-center for all 37 sub-mirrors of MB • Fixed on the middle of the focal plate for the image quality of the whole optical system

  39. C0-center for 37sub-mirrors of MB

  40. Co-focus + aspheric surface shape for 24 sub-mirrors of MA

  41. Nov. 21, 2008optical image quality 80%光浓度平均值 =0.509角秒， 80%光浓度最好值 =0.25角秒 Statistic of image quality ° m=7.2, exposure time 1 m tracking started at d=24.25°, t=2.22 Measured Image during observation for 132 minutes

  42. Test result by guiding cameras • Four guiding cameras located on the focal surface with field of view 3.2°

  43. April 25, 2009 with 3.2° FOV • FWHM<10pixel, about 2 arc seconds Active corrected to 0.3-0.4arcsec With Seeing 1.7-2 arcsec

  44. Contribution in development of active optics

  45. Active Optics in LAMOST • Aspherical surface of mirrors created from plano via active control; • A combination of segmented mirror active optics and thin deformable mirror active optics on one mirror; • Two large segmented mirrors needed to be actively controlled in the same time in the telescope; • With hexagonal deformable sub-mirrors; • Wave front sensing on a variable aperture; • Close loop control combine with open loop control; • S-H wave front sensing combine with edge sensing.

  46. Progress in active optics • Segmented active optics developed in Keck is a great progress in astronomical telescope, open a new way to build very large, even extremely large telescopes. • Thin deformable mirror active optics developed in NTT and VLT , break through bottleneck of 5 to 6 meters aperture of the large telescope, and started to build very large monolithic mirror telescope with a best image quality. • Based on their pioneer work and some study and experiments in China, we developed the new type of active optics—an active optics combine both segmented and thin deformable mirror active optics

  47. VLT 8m primary Keck 10m primary LAMOST Circle: force actuator Dot: displacement actuator

  48. Contribution in active optics by LAMOST • Using active optics to create aspheric mirror surface from plano, except for maintaining mirror surface shape by correcting gravitational and thermal deformations; • Applying active optics to realize a variable mirror surface shape optical system which could not be obtained by conventional optical design; • Combine both of the segmented and the thin deformable mirror active optics, which could let extremely large telescope adopting larger size segments (sub-mirrors), and could be useful to build the even extremely large telescope.

  49. Prospect • 2009-2010: Engineering commissioning • 2011: Science commissioning • 2012-2015: Regular spectroscopic survey • 2011-2015 Start southern LAMOST project for all sky survey

  50. Preliminary configuration for LAMOST South

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