1. An IFU for IFOSC on IUCAA 2m Telescope
A. N. Ramaprakash
Inter-University Centre for Astronomy & Astrophysics, Pune
Abhay, Atul, Hillol, Kalpesh, Mahesh, Moin, Mudit, Pravin,
Ranjan, Shyam, Sujith, Swapnil, Vilas

2. IFU on IUCAA 2 m Telescope
Plan of the Talk
Telescope and IFOSC parameters
Basic structure of the system
Constraints on IFU Design for IFOSC on IUCAA Telescope
IFU on IUCAA 2 m Telescope
Design and
Performance of the IFU
Basic Design
Selection criteria for parameters
Performance
IFOSC performance with IFU / Summary
A. N. Ramaprakash, IUCAA

3. Techniques for 2-D Spectroscopy
A. N. Ramaprakash, IUCAA

4. Built by Telescope Technologies Ltd., Liverpool, UK Location
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
A. N. Ramaprakash, IUCAA

5. Observatory Views
A. N. Ramaprakash, IUCAA

6. IUCAA Girawali Observatory
A. N. Ramaprakash, IUCAA

7. The 2m Telescope
A. N. Ramaprakash, IUCAA

8. V-band median seeing in winter - 1.2" Extinction (mag./airmass)
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)
A. N. Ramaprakash, IUCAA

9. IFOSC & Calibration Unit PI CCD NIPI Next Generation
Instruments
IFOSC & Calibration Unit
PI CCD
NIPI
Next Generation
Five Year Plan
A. N. Ramaprakash, IUCAA

10. 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
 = 0.35m to  = 0.85m
Polarimetry mode
2K x 2K EEV CCD with 13.5m2 pixels
40m/arcsec plate scale on CCD at f/4.5 (demagnification of 2.2)
A. N. Ramaprakash, IUCAA

11. Direct Cassegrain Port
F/10 Beam
Primary Mirror
Side Port
A & G Unit
Lamps
Calibration Unit
IFOSC
IFOSC Object Plane
/ Telescope Focal Plane
CCD Detector
A. N. Ramaprakash, IUCAA

12. / Telescope Focal Plane
Calibration Unit
Primary Mirror
Side Port
A & G Unit
Lamps
Folding Mirror
Calibration Unit
IFOSC
IFOSC Object Plane
/ Telescope Focal Plane
CCD Detector
A. N. Ramaprakash, IUCAA

13. / Telescope Focal Plane
Cassegrain Side Port
Primary Mirror
Side Port
Instrument
Folding Mirror
A & G Unit
Lamps
Calibration Unit
IFOSC
IFOSC Object Plane
/ Telescope Focal Plane
CCD Detector
A. N. Ramaprakash, IUCAA

14. IFU on IUCAA Telescope : Design Constraints
Mechanical Constraints
Can’t put Fibre-slit directly at the
IFOSC object plane
Dimension of the CCD + De-magnification of the IFOSC
Maximum Dimension of Projected Fibre Slit
on the IFOSC Object Plane ~ 59 mm
A. N. Ramaprakash, IUCAA

15. IFU on IUCAA Telescope : Design Constraints
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 =
μm2 - steradians
A. N. Ramaprakash, IUCAA

16. Basic Design Configuration of the IFU
Fore-Optics
Lenslet + Fibre
Unit
Output Optics
IFU
Teles-cope
Spectro-graph
Necessary magnification
Proper sampling.
Telecentric Output
To couple fibre Slit to the Spectrog.
Change the f/# of the beam
Telecentric Output
To Sample the sky image
Feed light into the fibre with proper f/#
A. N. Ramaprakash, IUCAA

17. Mechanical Configuration of the IFU
Fore - Optics
Lenslet +
Fibre Unit
Fibre Slit
Primary Mirror
Integral Field Unit
(IFU)
A & G Unit
Output Optics
Lamps
This distance has
To be > 80 mm
(Opto-Mechanical Design
Constraints)
IFOSC Object Plane
/ Telescope Focal Plane
Image of Fibre Core
~ Slit
A. N. Ramaprakash, IUCAA

18. IFU on IUCAA Telescope : Design Constraints
Focal Ratio Degradation (FRD)
(F/#)out < (F/#)in
Due to Micro-bending/Manufacturing
Defects
Statistical property
Results in increase of (AΩ) product
FRD should be minimized
A. N. Ramaprakash, IUCAA

19. Focal Ration Degradation
(Carrasco & Parry, 1994, MNRAS, 271,1-12)
A. N. Ramaprakash, IUCAA

20. Design Optimization of the IFU
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
A. N. Ramaprakash, IUCAA

21. Design Optimization of the IFU
BUT
IFOSC accepts ‘F/10’ beam
F/#
IFOSC
F/10
Output Optics
Fibre Core
Magnification = 10 / (F/#) = M
The projected slit width = M X Fibre Core Diameter
‘M’ affects the Spectral resolution
A. N. Ramaprakash, IUCAA

22. Design Optimization of the IFU
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 +
Aberrations &Throughput
Recipe for Design Optimization
A. N. Ramaprakash, IUCAA

23. Basic scientific constraints of the IFU
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)
A. N. Ramaprakash, IUCAA

24. Fore-optics, Lenslets and Fibres
Telescope Focal
Plane
Lenslet + Fibre
Unit u v d
Singlet field flattener for telecentric output
Achromatic doublet
f2 ~ 508mm, v = 10mm, Lenslet Φ= 2.1 mm
For different sampling scales,
MFore-optics=f2/f1 (17.2, 21.8, 25.75);
L2 & v kept fixed; Only L1, u and f1 changed.
A. N. Ramaprakash, IUCAA

25. Sampling Diameter at Telescope focal plane
Lenslet and Fibre
Dpupil f
DL= 2.1 mm
Magnified Image
by Fore-Optics
F/number of the Lenslet = 4
F/number of the telescope = 10
Sampling Diameter at Telescope focal plane
Lenslets provide continuous sampling of sky; they feed light into the fibre with the appropriate f/#.
A. N. Ramaprakash, IUCAA

26. Output Optics IFOSC Output Optics Output Magnification ‘M’
Fibre Core
Magnification = 10 / 4 = 2.5
Telecentric output
Projected slit width = 2.5 X 70μm (Fibre Core Dia.)
Maximum length of the Fibre Slit,
= 59 / 2.5 ~ 23.6 mm
A. N. Ramaprakash, IUCAA

27. Fore-optics layout – 1" per fibre sampling
A. N. Ramaprakash, IUCAA

28. Lenslet Optical Layout
A. N. Ramaprakash, IUCAA

29. Fore-optics Spot Diagram (1" sampling)
A. N. Ramaprakash, IUCAA

30. Output Optics Layout This distance to be kept > 80 mm 4.12.2007
A. N. Ramaprakash, IUCAA

31. Output Optics and IFOSC
A. N. Ramaprakash, IUCAA

32. Spot diagram at IFOSC object plane
A. N. Ramaprakash, IUCAA

33. Spot diagram at IFOSC detector plane
A. N. Ramaprakash, IUCAA

34. Fore-optics encircled energy diagram (1" sampling)
A. N. Ramaprakash, IUCAA

35. Encircled energy at IFOSC detector plane
A. N. Ramaprakash, IUCAA

36. (Ranjan Gupta et al., 2002, BASI, 30, 785)
Spectral Resolution
Slit width μm:
Grism
Peak (Angstrom)
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
3300 – 5540
9.02
IFOSC7
5000
3800 – 6840
9.68
IFOSC8
5800 – 8350
8.14
(Ranjan Gupta et al., 2002, BASI, 30, 785)
A. N. Ramaprakash, IUCAA

37. Sensitivity
A. N. Ramaprakash, IUCAA