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An IFU for IFOSC on IUCAA 2m Telescope

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. Plan of the Talk. Telescope and IFOSC parameters

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An IFU for IFOSC on IUCAA 2m Telescope

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  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. Plan of the Talk • 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 • IFU on IUCAA 2 m Telescope • Design and Performance of the IFU • IFOSC performance with IFU / Summary A. N. Ramaprakash, IUCAA

  3. Techniques for 2-D Spectroscopy http://www.cfai.dur.ac.uk/new/spectroscopy/spectroscopy.html A. N. Ramaprakash, IUCAA

  4. 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. 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. 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. 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. 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 • Dimension of the CCD + De-magnification of the IFOSC Can’t put Fibre-slit directly at the IFOSC object plane • Mechanical Constraints 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 Ω1 Ω2 A2 A1 AΩ = 94.265 μm2 - steradians • For 1 arc-sec sampling A1 . Ω1 = A2 . Ω2 • AΩ: Fixed by Telescope’s plate scale and F/number A. N. Ramaprakash, IUCAA

  16. Basic Design Configuration of the IFU IFU Output Optics Fore-Optics Lenslet + Fibre Unit • 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/# Teles-cope Spectro-graph A. N. Ramaprakash, IUCAA

  17. Mechanical Configuration of the IFU Fore - Optics Lenslet + Fibre Unit This distance has To be > 80 mm (Opto-Mechanical Design Constraints) Fibre Slit Output Optics Integral Field Unit (IFU) IFOSC Object Plane / Telescope Focal Plane Primary Mirror A & G Unit Lamps 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 • Further, invariance of AΩ Lower the (F/#)fibre Smaller the Fiber Core Diameter Better Spectral Resolution Smaller (F/#)fibre is desirable • To minimize FRD : (F / #)in < 5 so that, (F / #)out ~ (F / #)in A. N. Ramaprakash, IUCAA

  21. Design Optimization of the IFU • IFOSC accepts ‘F/10’ beam Output Optics IFOSC F/# F/10 Magnification = 10 / (F/#) = M Fibre Core • The projected slit width = M X Fibre Core Diameter ‘M’ affects the Spectral resolution BUT 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 Lenslet + Fibre Unit f1 f2 u F Telescope Focal Plane L1 L2 d v 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. Lenslet and Fibre DL= 2.1 mm Dpupil f F/number of the Lenslet = 4 F/number of the telescope = 10 Sampling Diameter at Telescope focal plane Magnified Image by Fore-Optics • Lenslets provide continuous sampling of sky; they feed light into the fibre with the appropriate f/#. A. N. Ramaprakash, IUCAA

  26. Output Optics • Output Magnification ‘M’ Output Optics IFOSC F/4 F/10 Magnification = 10 / 4 = 2.5 Fibre Core • 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 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. Spectral Resolution • Slit width - 220 μm: (Ranjan Gupta et al., 2002, BASI, 30, 785) A. N. Ramaprakash, IUCAA

  37. Sensitivity A. N. Ramaprakash, IUCAA

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