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The GMT Consortium Large Earth Finder Sagi Ben-Ami Smithsonian Astrophysical Observatory The Giant Magellan Telescope • The GMT is one of the three next generation optical telescope. • Segmented Gregorian design (six off axis and one on axis 8.4m mirrors) with an effective aperture of 25.4m diameter. • F/8.2 with a FoV of 24’. Plate Scale of 1’’ mm-1. • Site: Cerro Las Campanas in Chile’s Atacama desert. The GMT Consortium Large Earth Finder • The GMT Consortium Large Earth Finder (G-Clef) is a general purpose visible echelle spectrograph that offers precision radial velocity capabilities. • G-Clef was chosen as the 1st light instrument for the GMT. G-CLEF: Science Cases • Weighing planets in the TESS Catalogue. • O2 in the transmission spectra of exoplanets: A-Band absorption features between 7600-7700Å . G-CLEF: Science Cases • Near-field cosmology: Characterization of metal poor stars – the fossils of structure formation at the earliest phase after the big bang. • Flash Spectroscopy of SNe: Direct measurements of CSM composition, unique properties of the progenitor. Science Requirements So how do we achieve all of these ? • A fiber-fed high dispersion spectrograph thermally stabilized deployed at a gravity invariant location. • Pass band: 3500-9500Å • Different resolution is achieved by feeding the spectrograph with fibers of different core diameters. dl = Pw ' Optical Path: Fiber Run H O R IZ O N T A L A X IS N O T T O S C A L E B U FFER BU FFER C L A D D IN G BU FFER C L A D D IN G BU FFER C L A D D IN G (Pupil Slicer) C ORE C ORE C ORE 0 .6 5 C L A D D IN G C ORE 0 .2 0 0 .2 0 0 .4 9 0 .0 7 0 .7 6 0 .6 5 0 0 .3 8 0 .3 0 0 .3 2 5 Front-end F/# converters. 0 .3 4 0 .1 2 0 .1 4 0 .1 2 0 .3 8 0 .1 0 0 .1 0 0 .1 4 6 .0 0 N S-P R V M o d e PRV M o d e 6 .0 0 6 .0 0 M R M ode HT M ode PBS N O . D E S IG N E D BY: TO LERANC ES UNLESS O T H E R W IS E N O T E D S M I T H S O N IA N A S T R O P H Y S IC A L OBSERVATORY Vacuum Enclosure Interface ± 0 .X X = ± 0 .2 5 ± 0 .X = ± 0 .5 N O D E C IM A L = ± 1 AN G LE S = ±1º D R AFTED BY: C H EC KED BY: C O M P O N E N T M A T E R IA L : G R P LE AD A PP RO V AL: T H IR D A N G L E P R O J E C T IO N D E S C R IP T IO N F IB E R L A Y O U T C H IE F E N G APPR O VAL: SAO S H E E T S IZ E R E LEA SE D ATE: W O R KFLO W STATE: C O M PO N EN T W E IG H T (k g ): D W G N O . 1 0 0 A c o rn P a r k D r iv e C a m b rid g e , M A 0 2 1 4 0 T h e d a t a in t h i s d o c u m e n t i n c o r p o r a te p r o p r ie t a r y r ig h ts o f t h e S m it h s o n i a n A s t r o p h y s ic a l O b s e r v a t o r y . A n y p a r t y a c c e p t in g th is d o c u m e n t d o e s s o in c o n fid e n c e a n d a g r e e s t h a t i t s h a ll n o t b e d u p l ic a te d i n w h o l e o r in p a r t , n o r d i s c lo s e d t o o th e r s , w it h o u t t h e c o n s e n t o f t h e S m i t h s o n i a n A s t r o p h y s ic a l O b s e rv a to ry . R E V IS IO N B SC ALE SH EET (Scrambler) Spectrograph F/# converters. (Exposure Meter) 1 0 0 :1 1 O F 1 Spectrograph Optical Design Grating: A mosaic Mangin Fold Mirror of to three correct 300x400mm operating at a cylindrical fieldR4 curvature quasi-Littrow configuration. l d A d1 Â= = dl rf D G-Clef Red Camera • The re-designed red camera is a 7-element camera with one aspheric surface on the back surface of the 1st lens (Glass substrate). • Power is mainly due to CaF2 positive lenses, with i-line negative and meniscus lenses to control chromatic aberrations. Passband 5400-9520Å (Orders 65-113) Focal Length 450mm Beam Diameter 250mm FoV 7.7° Testable in collimated light (air-space). Yes Red Camera: PRV Ensquared Energy • Center-to-center distance between fibers in pseudo-slit increased to 170μm. • 80% Ensquared energy below 18μm (Nyquist for STA 9μm pixels) across the entire echellogram. Run 0HE081715AGs − Ensquared Energy 20 Fiber1 67% AHs Fiber1 80% AHs 15 10 5 5 15 20 0 Box Edge Size [mm] Box Edge Size [mm] Fiber2 67% AHs Fiber2 80% AHs Fiber6 67% AHs Fiber6 80% AHs 15 10 10 5 20 0 Fiber3 67% AHs Fiber3 80% AHs 15 5 20 0 Fiber7 67% AHs Fiber7 80% AHs 15 10 10 5 5 20 0 Fiber4 67% AHs Fiber4 80% AHs 15 20 0 10 5 5 5500 6000 6500 7000 7500 8000 Wavelength [Ang] 8500 9000 9500 10000 Fiber8 67% AHs Fiber8 80% AHs 15 10 0 5000 Fiber5 67% AHs Fiber5 80% AHs 15 10 20 0 Run HE081715AGs − Ensquared Energy 20 0 5000 5500 6000 6500 7000 7500 8000 Wavelength [Ang] 8500 9000 9500 10000 X-dispersers: VPH Gratings • VPH Grating: A modulation in the index of refraction induced by holographic exposure of dichromatic gelatin. • Higher efficiency than common ruled gratings. Blue X-disperser: A VPH-Prism. VPH Gelatin AoI and AoE 13 12 11 Angle (deg) 10 9 8 7 6 5 4 3000 3500 4000 4500 Wavelength [Ang] 5000 5500 VPH Ghosts Mitigation: Tilted Fringes • Narcissistic Ghosts: Scattering from Gelatin-Glass interface after reflection from the detector m= 1; m`= 0. • Littrow ghost: Recombination of cross dispersed orders by the VPH Dm= 0 . sin b ' = Dml + sin a s cos g Tilted Fringes • By introducing a tilt to the imprinted fringes, we move the operation wavelength away from the Littrow configuration. • The tilt should be large enough so that the ghosts are moved away from the detector. é ù æ sin a ö sin b B = n2 sin ê arcsin ç - 2f ú ÷ è n2 ø ë û Db = a - b B Narcissistic Ghost • The increased VPH-camera angle deflects ghost beams to higher angles. Detector Refl ect ed B Na rci ssi sti c Be am s eam s Littrow Ghost • Tilted fringes ensure that we no longer operate in Littrow configuration, and so the recombined rays miss the detector after recombination. Detector Red Arm Echellogram • Entire Echellogram fits well onto the detector (92.4×92.2mm), with at least 1mm for alignment in each direction. 43 42.5 [mm] 42 41.5 41 40.5 40 −21.5 −21 −20.5 −20 −19.5 −19 [mm] Blue Arm Echellogram • Entire Echellogram fits well onto the detector (92.4×92.2mm), with at least 0.5mm for alignment in each direction.