The GMT Consortium Large Earth Finder. Sagi Ben-Ami Smithsonian Astrophysical Observatory

Transcription

1 The GMT Consortium Large Earth Finder Sagi Ben-Ami Smithsonian Astrophysical Observatory

2 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.

3 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.

4 G-CLEF: Science Cases Weighing planets in the TESS Catalogue. O2 in the transmission spectra of exoplanets: A-Band absorption features between Å.

5 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.

6 Science Requirements

7 So how do we achieve all of these? A fiber-fed high dispersion spectrograph thermally stabilized deployed at a gravity invariant location. Pass band: Å Different resolution is achieved by feeding the spectrograph with fibers of different core diameters. dl = Pw '

8 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 C L A D D IN G C ORE Front-end F/# converters N S-P R V M o d e PRV M o d e 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.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 A c o rn P a r k D r iv e C a m b rid g e, M A 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 1 O F 1

9 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

10 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 Å (Orders ) Focal Length 450mm Beam Diameter 250mm FoV 7.7 Testable in collimated light (air-space). Yes

11 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 Fiber2 67% AHs Fiber2 80% AHs 15 Box Edge Size [mm] Box Edge Size [mm] Fiber5 67% AHs Fiber5 80% AHs Fiber6 67% AHs Fiber6 80% AHs Fiber3 67% AHs Fiber3 80% AHs Fiber7 67% AHs Fiber7 80% AHs Fiber4 67% AHs Fiber4 80% AHs Wavelength [Ang] Fiber8 67% AHs Fiber8 80% AHs Run HE081715AGs Ensquared Energy Wavelength [Ang]

12 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 Angle (deg) Wavelength [Ang]

13 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

14 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

15 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

16 Littrow Ghost Tilted fringes ensure that we no longer operate in Littrow configuration, and so the recombined rays miss the detector after recombination. Detector

17 Red Arm Echellogram Entire Echellogram fits well onto the detector ( mm), with at least 1mm for alignment in each direction [mm] [mm]

18 Blue Arm Echellogram Entire Echellogram fits well onto the detector ( mm), with at least 0.5mm for alignment in each direction.