An IFU for IFOSC on IUCAA 2m Telescope A. N. Ramaprakash Inter-University Centre for Astronomy &...
-
Upload
alaina-golden -
Category
Documents
-
view
216 -
download
1
Transcript of An IFU for IFOSC on IUCAA 2m Telescope A. N. Ramaprakash Inter-University Centre for Astronomy &...
An IFU for IFOSC on IUCAA 2m Telescope
A. N. RamaprakashInter-University Centre for Astronomy & Astrophysics, Pune
Abhay, Atul, Hillol, Kalpesh, Mahesh, Moin, Mudit, Pravin, Ranjan, Shyam, Sujith, Swapnil, Vilas
4.12.2007 A. N. Ramaprakash, IUCAA 2
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
aiIFU on IUCAA 2 m
Telescope
Design and Performance of the IFU
IFOSC performance with IFU / Summary
• Telescope and IFOSC parameters• Basic structure of the system• Constraints on IFU Design for IFOSC on IUCAA Telescope
• Basic Design• Selection criteria for parameters • Performance
Plan of the Talk
4.12.2007 A. N. Ramaprakash, IUCAA 3
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
http://www.cfai.dur.ac.uk/new/spectroscopy/spectroscopy.html
Techniques for 2-D Spectroscopy
4.12.2007 A. N. Ramaprakash, IUCAA 4
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
A glimpse of IGO
Built by Telescope Technologies Ltd., Liverpool, UK
Location Girawali - 80km NE from Pune, near Junnar Altitude - ~1000m above MSL
Telescope Specification - 2m, f/10, Ritchey Chrétien, 6’
radius field Wide Field Corrector to extend field to 21’
radius Mount – Alt-Az on hydrostatic bearings Focus – Cassegrain (1 direct & 4 side ports) Active pneumatic mirror support (20cm
thick) Integrated Autoguider
4.12.2007 A. N. Ramaprakash, IUCAA 5
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Observatory Views
4.12.2007 A. N. Ramaprakash, IUCAA 6
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
IUCAA Girawali Observatory
4.12.2007 A. N. Ramaprakash, IUCAA 7
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
The 2m Telescope
4.12.2007 A. N. Ramaprakash, IUCAA 8
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Site Vital Statistics
V-band median seeing in winter - 1.2" Extinction (mag./airmass)
B – 0.26 to 0.74 V – 0.14 to 0.38
Sky Brightness (mag/sq. arcsec) B – 21.8 V – 20.8 R – 19.3
Cloud cover over a period of six months (Nov. – April) 50% photometric 80% spectroscopic
(Das et. al, ’99,BASI 27,609)
4.12.2007 A. N. Ramaprakash, IUCAA 9
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Instruments
IFOSC & Calibration Unit
PI CCD NIPI Next GenerationFive Year Plan
4.12.2007 A. N. Ramaprakash, IUCAA 10
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
IUCAA Faint Object Spectrograph Camera (IFOSC)
UBVRI filters 0.8”, 1”, 1.5”, 2” x 11’ slits 10 grisms (2 echelle & 2 cross
dispersers) R = 190 to R = 3700 = 0.35m to = 0.85m Polarimetry mode 2K x 2K EEV CCD with 13.5m2 pixels 40m/arcsec plate scale on CCD at
f/4.5 (demagnification of 2.2)
4.12.2007 A. N. Ramaprakash, IUCAA 11
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Primary Mirror
Calibration Unit
IFOSC
CCD Detector
Lamps
IFOSC Object Plane/ Telescope Focal Plane
A & G Unit
Side Port
F/10 Beam
Direct Cassegrain Port
4.12.2007 A. N. Ramaprakash, IUCAA 12
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Primary Mirror
Calibration Unit
IFOSC
CCD Detector
Lamps
IFOSC Object Plane/ Telescope Focal Plane
A & G Unit
Side Port
Folding Mirror
Calibration Unit
4.12.2007 A. N. Ramaprakash, IUCAA 13
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Primary Mirror
Calibration Unit
IFOSC
CCD Detector
Lamps
IFOSC Object Plane/ Telescope Focal Plane
A & G Unit
Side PortInstrument
Folding Mirror
Cassegrain Side Port
4.12.2007 A. N. Ramaprakash, IUCAA 14
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Dimension of the CCD + De-magnification of the IFOSC
Maximum Dimension of Projected Fibre Slit on the IFOSC Object Plane ~ 59 mm
Mechanical Constraints
Can’t put Fibre-slit directly at the
IFOSC object plane
IFU on IUCAA Telescope : Design Constraints
4.12.2007 A. N. Ramaprakash, IUCAA 15
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Area–Solid Angle Product (AΩ) : Invariant
Optical System
A1
Ω1
A2
Ω2
A1 . Ω1 = A2 . Ω2
AΩ : Fixed by Telescope’s plate scale and F/number
For 1 arc-sec sampling
AΩ = 94.265 μm2 - steradians
IFU on IUCAA Telescope : Design Constraints
4.12.2007 A. N. Ramaprakash, IUCAA 16
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Teles-cope
Spectro-graphFore-Optics Lenslet + Fibre
UnitOutput Optics
IFU
• Necessary magnification
• Proper sampling.
• Telecentric Output
• To Sample the sky image
• Feed light into the fibre with proper f/#
• To couple fibre Slit to the Spectrog.
• Change the f/# of the beam
• Telecentric Output
Basic Design Configuration of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 17
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Primary Mirror
Lamps
IFOSC Object Plane/ Telescope Focal Plane
A & G Unit
Fore - OpticsLenslet
+Fibre Unit
Fibre Slit
Output Optics
Image of Fibre Core ~ Slit
Integral Field Unit(IFU)
This distance has To be > 80 mm
(Opto-Mechanical Design Constraints)
Mechanical Configuration of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 18
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Focal Ratio Degradation (FRD) (F/#)out < (F/#)in
• Due to Micro-bending/ManufacturingDefects
• Statistical property
• Results in increase of (AΩ) product
IFU on IUCAA Telescope : Design Constraints
FRD should be minimized
4.12.2007 A. N. Ramaprakash, IUCAA 19
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Focal Ration Degradation
(Carrasco & Parry, 1994, MNRAS, 271,1-12)
4.12.2007 A. N. Ramaprakash, IUCAA 20
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
To minimize FRD : (F / #)in < 5 so that,
(F / #)out ~ (F / #)in
Further, invariance of AΩ
Lower the (F/#)fibre
Better Spectral Resolution
Smaller the Fiber Core Diameter
Smaller (F/#)fibre is desirable
Design Optimization of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 21
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
IFOSC accepts ‘F/10’ beam
F/# IFOSCF/10Output Optics
Fibre Core
Magnification = 10 / (F/#) = M
BUT
The projected slit width = M X Fibre Core Diameter
‘M’ affects the Spectral resolution
Design Optimization of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 22
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
The maximum length of the Fibre Slit = 59 mm / M
‘M’ restricts the total numbers of fibres
It is preferred to keep ‘M’ as low as possible.
(F/#)fibre should be made as large as possible
Recipe for Design Optimization
+Aberrations &Throughput
Design Optimization of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 23
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai Optimized for the wavelength range 4500 – 8500 Å
The sky area would be sampled by 100 Lenslets + Fibres
Three spatial sampling scales 1.0" per fibre, 0.8" per fibre and 1.2" per fibre are being used.
The sky area sampled by IFU ~ 14 arc-sec X 7 arc-sec (For the case of 1 arc-sec per fibre)
Basic scientific constraints of the IFU
4.12.2007 A. N. Ramaprakash, IUCAA 24
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
f2 ~ 508mm, v = 10mm, Lenslet Φ= 2.1 mm
Fore-optics, Lenslets and Fibres
F
f1 f2
L1
L2
Telescope Focal
Plane
Lenslet + Fibre
Unitu
vd
For different sampling scales, MFore-optics=f2/f1 (17.2, 21.8, 25.75); L2 & v kept fixed; Only L1, u and f1 changed.
Singlet field flattener for telecentric output
Achromatic doublet
4.12.2007 A. N. Ramaprakash, IUCAA 25
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Magnified Image by Fore-Optics
Dpupil
f
DL= 2.1 mm
/#
/#L
pupil samp
teles
FD D
F
F/number of the Lenslet = 4
F/number of the telescope = 10
Sampling Diameter at Telescope focal
plane
Lenslet and Fibre
Lenslets provide continuous sampling of sky; they feed light into the fibre with the appropriate f/#.
4.12.2007 A. N. Ramaprakash, IUCAA 26
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Output Magnification ‘M’
F/4 IFOSCF/10Output Optics
Fibre Core
Magnification = 10 / 4 = 2.5
Projected slit width = 2.5 X 70μm (Fibre Core Dia.)
Maximum length of the Fibre Slit, = 59 / 2.5 ~ 23.6 mm
Output Optics
Telecentric output
4.12.2007 A. N. Ramaprakash, IUCAA 27
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Fore-optics layout – 1" per fibre sampling
4.12.2007 A. N. Ramaprakash, IUCAA 28
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Lenslet Optical Layout
4.12.2007 A. N. Ramaprakash, IUCAA 29
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Fore-optics Spot Diagram (1" sampling)
4.12.2007 A. N. Ramaprakash, IUCAA 30
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Output Optics Layout
This distance to be kept > 80 mm
4.12.2007 A. N. Ramaprakash, IUCAA 31
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Output Optics and IFOSC
4.12.2007 A. N. Ramaprakash, IUCAA 32
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Spot diagram at IFOSC object plane
4.12.2007 A. N. Ramaprakash, IUCAA 33
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Spot diagram at IFOSC detector plane
4.12.2007 A. N. Ramaprakash, IUCAA 34
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Fore-optics encircled energy diagram (1" sampling)
4.12.2007 A. N. Ramaprakash, IUCAA 35
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Encircled energy at IFOSC detector plane
4.12.2007 A. N. Ramaprakash, IUCAA 36
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Slit width - 220 μm:
Spectral Resolution
Grism Peak (Angstro
m)
Wavelength range
(Angstroms)
Spectral resolution
(Angstrom for 2.2 arc-sec slit)
IFORS 5 4000 3300 – 6300 20.02
IFOSC5 6000 5200 – 10300 20.24
IFORS1 4000 3300 – 5540 9.02
IFOSC7 5000 3800 – 6840 9.68
IFOSC8 6000 5800 – 8350 8.14
(Ranjan Gupta et al., 2002, BASI, 30, 785)
4.12.2007 A. N. Ramaprakash, IUCAA 37
IRS
IS M
eeti
ng,
TIF
R,
Mu
mb
ai
Sensitivity