The GMT-CfA/Carnegie/Catolica/Chicago Large Earth Finder (G-CLEF): A Versatile, Optical Echelle Spectrograph for the GMT

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1 The GMT-CfA/Carnegie/Catolica/Chicago Large Earth Finder (G-CLEF): A Versatile, Optical Echelle Spectrograph for the GMT Andrew Szentgyorgyi NAOC/ 11 Nov 2011 G- CLEF Team: G. Furesz/CfA Proj. Sci. A. Frebel/CfA Science W.G. Chair T. Norton/CfA Proj. Manager E. Hertz/CfA Proj. Eng. J. De Ponte- Evans/CfA SW Sys. Eng. I. Evans/CfA SW ScienQst J. Bean/Chicago Cal. Sys. Sci J. Crane/Carnegie Tel. Interf. Sci. D.Guzman/Catolica Imager Sci. A. Jordan/Catolica Simul. Sci. A. Uomoto/Carnegie Tel. Interf. Manager We wish to thank the NSF for partial support of this study through grant number AST

2 From Hectospec/chelle to LAMOST 300 Fibers 4000 Fibers!

3 Talk Summary Introduction to/status of the GMT Science goals for G-CLEF Flowdown to the G-CLEF system design The G-CLEF design Issues related to precision radial velocity performance

4 Giant Magellan Telescope Introduction & Status 5

5 GMT Consortium Membership Carnegie Harvard KASI U. Arizona Chicago SAO U. Texas Austin Texas A&M ANU AAL % subscribed LCO

6 Giant-Segmented Mirror Telescope 7 x 8.4m primary mirror segments 380 square meters of collecting area (22-m equivalent diameter) f/0.7 primary focal ratio Gregorian Optical design Segmented secondary The GMT Concept

7 Adaptive Secondary Mirror Telescope structure Interface Hexapod Wind shield DM assembly Cold plate Reference Body Face sheet Controller Secondaries m Diameter

8 Adaptive Optics System 6 Sodium layer lasers 3 launch points

9 Polishing First Off-Axis GMT Primary Segment Near Completion

10 The GMT Concept 2 Optical Prescriptions

11 First Off Axis Primary (GMT1) Surface Maps 71 nm 66 nm 38 nm June July August The current surface accuracy is 23 nm rms

12 Primary Mirror Segment Production GMT1 Completion 11/11 Final figuring & acceptance testing GMT2 Casting 01/12 Mold assembly GMT3 Casting 02/13 Material deliveries Segments 4-8 at ~ 12 month intervals Nominal Peak Temperature Date for GMT2: Jan 12, 2012

13 Las Campanas Observatory GMT Here Australia/New Zealand Manquis Ridge (2308 m) (DuPont 100 telescope) Manqui Pk. (2450 m) (Magellan 6.5m telescopes) Campanas Pk. (2551 m) Alcaino Pk. (2410 m) Pan American Hwy (Route 5)

14 Seeing at the GMT Site Las Campanas Seeing Statistics Seeing Percen*les 10% 25% 50% 75% 90% Manquis Ridge Co. Manqui Co. Alcaino Co. Las Campanas

15 Site Preparation Start early 2012

16 First Light Instrument Selection Six concepts under study TIGER AO IR Imager GMACS Optical MOS G-CLEF Opt. Echelle GMTNIRS IR Echelle GMTIFS NIR IFU Spect NIRMOS NIR MOS (MANIFEST MOS Fiber Feed) Review panels have met: members involved in E-ELT, TMT, JWST, LSST Selection Panel meets in November First light instruments will proceed Final selection ~ Mar 2012 Commence instrument build ~ Jan 2013

17 Below IP: Gregorian Instrument Rotator ~4 Large instruments (e.g., NIRMOS) Instrument Mounting Top of Rotator: Instrument Platform ~3 Small instruments (AO-fed plus tertiary)

18 Instrument Mounting GMTNIRS GMTIFS TIGER NIRMOS GMACS G-CLEF

19 G-CLEF Echelle Spectrograph Optical Band, Fiber-fed Echelle spectrograph 4.5 m Multi-Purpose - emphasis on PRV Fiber mode scrambler Extreme thermal control Vacuum enclosure Gravity invariant mounting Extremely high throughput 2.3 m 2.4 m

20 The G- CLEF Science Case.

21 The Search for Fossil Stars Requires Good Blue Sensi*vity.

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23 Exoplanet science goals for G- CLEF: The discovery of a rocky, earth- like planet in a habitable zone. The discovery of rocky, earth- like planets orbiqng solar type stars in their habitable zones Understand the generality or uniqueness of our solar system Requires discovery transiqng systems for which we subsequently measure the reflex moqon of the star to determine the mass of all/most of the consqtuent planets v NAOC PRVv ASz Beijing v CfAv Nov Oct v ASz v

24 Exoearth Science Requires More Precise RV Measurements.

25 We Now Live in the Kepler Era. Launch 6 Mar 2009

26 Kepler has already increased the census of transit planets x30 Kepler-16(AB)ba: Saturn-like planet orbiting two stars Kepler-11b,c,d,e,f & g: The richest transiting-planet system Kepler-9a&b: First unambiguous dynamical transittiming variations. Jason Rowe Daniel Fabrycky

27 Mass + Radius Informa*on Permits Determina*on of Exoplanet Geology

28 Toblerone (Ternary Diagrams) Valencia, Sasselov & McConnell

29 Entering the Transi*ng Exoplanet Survey Satellite (TESS) Epoch Soon.. TESS Mission George Ricker, PI MIT, Goddard, SAO & cast of thousands All sky survey to search for transit planets around stars to >10th mag. TESS selected for Phase A study by NASA

30 Beyond Kepler CoRoT, Kepler and PLATO survey fields PLATO & TESS will open the southern skies for transiting exoplanet survey. TESS will survey the entire (Southern) sky!

31 Abundance studies across the Local Group and Beyond Detection, census of the most metal poor stars Extended blue response High resolution Detailed Chemical Composition Beyond the Local Group Slit Length for MOS Gamma Burst Science, High Z IGM & ISM Gamma ray burst science / ISM at very high Z Studies of IGM at high Z Constancy of α & µ over cosmological time scales Extended red response Detection, census & characterization of exoearths by PRV Instrument Changeover Speed Science Flowdown to Instrument Requirements Long term wavelength scale stability Very high resolution High S/N

32 Requirements for Exoearth Mass Measurements The ability to detect planets transits of exoearths and measure the reflex moqon of their host stars on year- to- mulqyear Qmescales Detect the presence of earth mass planets Earth-sun reflex (K) ~ 10 cm/sec State of the art is ~ 1 m/s State of the art è millipixel doppler shifts at focal plane ~ 150 Å Finding earth analogues requires at least 10x beber precision v NAOC PRVv ASz Beijing v CfAv Nov Oct v ASz v

33 Thermal and Mechanical Stability Requirements for PRV Extremely high thermal and mechanical stability requirements drive design to: Vacuum enclosure for thermal isolation Gravity invariant mounting Fiber feed for thermal isolation Elimination of heat sources on or near spectrograph Pressure stabilization required to stabilize ambient index of refraction

34 The Need for Vacuum Enclosure: Comparison of HARPS (high thermal stablity, vacuum enclosed, fiber fed echelle) and HIRES Calibrated with ThAr

35 Op*cal Fiber Feed Length Affect Blue Response Short fiber are good

36 Spectrograph Resolu*on is Primary Determinant of Spectrograph Radial Velocity Precision Steeper features are more sensitive to doppler shifts than broader features Resolution is the measure of ability to measure steep features High resolution = precise radial velocity determination

37 Precision Radial Velocity & Resolu*on From Bouchy, Pepe & Queloz 2001, A & A, 374, 733

38 Resolu*on: Spectrograph Beam Size Liouville s theorem dictates that for a given slit size and graqng blaze, the raqo of the telescope primary diameter to the spectrograph beam size specifies the resoluqon of the spectrograph For 1 arcsec, R = 10 5, φ T = mm & Tan(θ)=4 φ T = 317 mm This will drive the diameter of lens substrate to very expensive and poten*ally unobtainable diameters

39 Asymmetric White Pupil Configura*on Reduces Requirements for Lens Substrate Diameter Reducing beam size increases included angles more challenging optical design

40 Two camera design with red and blue refrac*ve cameras improves performance, reduces cost and technical risk Response of red and blue camera CCDs can be optimized o Deep depletion devices to boost red response Coatings can be tailored for red and blue channels Reduced passband for each channels reduces difficulty of optical design Reduced lens count Substrates for lenses can be optimized for each channel

41 Comparison of e2v Regular and Deep Deple*on CCD Quantum Efficiency

42 Four Resolution Modes High Throughput (HT) R = 20,000 / φ Fib = 1.2 Precision Abundance (PA) ) R = 40,000 / φ Fib = 0.7 Precision Radial Velocity (PRV) ) R = 110,000 / φ Fib = 0.7 o Pupil Sliced (?) High Resolution (HR) R = 150,000 / φ Fib = 1.2 o Image Sliced Operating Passband: 3500Å 9500Å Camera Beam Diameter: 200 mm Peak Efficiency: 35% G-CLEF Parameters

43 Telescope Beam Plenum Outer Thermal Enclosure Inner Thermal Enclosure Blue Grism & Camera G-CLEF System Diagram Dichroic Collimator, Grating Changer & Pupil Transfer Fiber Selector Scramblers Instrument Platform Precision Radial Velocity Front End High Resolution Front End High Throughput Front End ADC Orientable Tip Tilt Calibration System (Location TBD) Hollow Cathode & Incanc. Calibrator Frequency Comb Calibrator Focal Reducer, Shutter & Filter Wheel Deployable Iodine Filter Deployable Screen Tunable Laser Calibrator Convective Heat Exchange Imsulated Floor Red Grism & Camera Vibration Isolation Convective Heat Exchange Calibration Lamp Box (ThAt + Incan) Multi Object Spectroscopic Feed Laser Calibrator Injector Coude Platform Gregorian Focus

44 G-CLEF Mounting on the GMT

45 M1 Mirror Echelle Grating Dichroic Fiber Input M2 Mirror Fold Mirror ~ 1.3 m Cross Dispersers Red Camera Blue Camera ~ 3.6 m

46 4.5m Spectrograph Weights (not optimized): Vacuum Vessel Assembly = 3,100 kg (6,834 lb) Spectrograph Bench Assembly = 5,900 kg (13,007 lb) Total = 9,000 kg (19,841 lb) 2.4m 2.3m

47 Fiber Input Port Vacuum Vessel Optics Bench Vacuum Vessel Access Cover Isolator Stack - Bench Isolator Stack Vacuum Vessel

48 Vacuum Vessel Design & Analysis Vacuum Vessel Mechanical Design Vacuum Vessel Structural Analysis Vacuum Chamber (6061-T6 aluminum) 2.4 m 4.5 m 2.3 m Assembly Mass = ~ 3100 kg (vessel and internal thermal shields) (not optimized)

49 Lens Mounts Design & Analysis Lens Mounts Mechanical Design Cross Disperser Mount Mechanical Design Lens Mounts Structural Analysis VPH Gratings Lens 1 Lens 2 & 3 Lens 4 Lens 5 Lens 6 Lens 7 & 8 Blue Camera Cryostat Lens 5 Bezel Assembly ~1 m Blue Camera Weights (not optimized): Optics Only = 35 kg ( 77 lb) Bezels and Support = 112 kg (247 lb) Cryostat = 12 kg ( 26 lb) Total = 159 kg (350 lb)

50 Zerodur Bond Spacer Gra7ng Monolith Design & Analysis Epoxy Channel Zerodur Grating Facet 275 mm Zerodur Substrate 1260 mm 320 mm Mass = ~250 kg Michelson Echelon

51 15.0% Total System Efficiency Everything is included except atmosphere: telescope front end optics (tertiary, relay optics, ADC) fiber system (Fresnel losses, slit losses, FRD losses, internal transmission) spectrograph (f-ratio conversion, gratings, optics, detector) 10.0% Throughput [%] 5.0% all-fiber all-relay hybrid - baseline 0.0% Wavelength [nm]

52 PRV Error Sources. Note: HARPS achieves month-long 15 cm/s stability against ThAr calibrator

53 A Gold-Plated Exoplanet? From Wright, 2009

54 Or a case of the jitters?

55 New techniques for more precise wavelength calibrators Laser frequency combs Ultrastabilized etalons

56 Workhorse Wavelength Calibrator ThAr HC has significant weaknesses: Faintness Irregular fiducial amplitude Wavelength deserts Each lamp has personality

57 Year-long and decadal velocity precision requires calibrator reference stabley controllable parameters atomic clock/precision metering structures

58 Lasers Are Versatile Calibrators at Red Wavelengths ~8500Å, Ca IR triplet. Tunable Laser Calibration Frame ThAr Calibration Frame n.b.: Scattering, fringing, saturation. effects

59 ASZ v PUCv 2009 Oct 5

60 Repeatedly pulsing laser T Rep τpulse 1/τ pulse

61 Calibrator Stability & Feature Density Comb laser are expensive and operationally complicated, but ultrastable etalons appear to be a good alternative next generation calibrator Recent HARPS data demonstrates better than 10 cm/s stability over 24 hours with ultrastable etalons

62 Red Comb Laser

63 Comb laser capabilities Comb laser = octave spanning, mode locked femtosecond frequency comb lasers Comb lasers may make it possible to enable PRV ~ 1 cm/sec Precision wavelength calibration 1:10 15, with long-term stability Precision result of fundamental physical parameters Regular, tunable grid of isointensity fiducials No deserts or Ar hotspots found in ThAr HCL Potential for broad (UV-NIR) wavelength

64 However, comb lasers that cover the entire optical passband are still in the future. Geneva ultrastable etalon can bootstrap stability of comb lasers across optical band and bridge gaps in frequency coverage. See Wildi et al A Fabry-Perot calibrator of the HARPS radial velocity spectrograph: performance report, Proc. SPIE

65 A Green Laser Comb air voids Photonic Crystal Fiber (PCF) Green source comb (green shaded area) generated from a 1 GHz Ti:sapphire frequency comb (red curve).

66 A Schema*c Spectrograph A spectrograph produces a monochromaqc image of the input fiber/slit on the focal plane of the spectrograph detector

67 Fiber Scrambling Several approaches have been tried to scramble the radial informaqon Crushers Double scramblers Integrating spheres Fiber scramblers

68 Problems in the Near Field: Structure Produced by Seeing and Guiding

69 Scrambling with Square Fibers from Gabor s Furesz s fiber test facility