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

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.