CASE spectrograph Spectrograph Optical Specifications Spectrograph Optical Design Spectrograph Mechanical and Electrical Design Calibration System: Lamps, Sky Lines, Stars, CCD Flat Field Illuminator By Justo Sanchez Instituto de Astrofísica de Andalucía (CSIC) Granada

Spectrograph on Telescope, Specifications Basically, the CASE spectrograph will be based on the DESI spectrographs, but using only two arm, BLUE and RED. The telescopes, focal plate & positioner specification are: parameter DESI CASE Telescope/FOV MAYAL (Ø4m)/3⁰ Schmidt (Ø0.8m)/8⁰ Focal Plate (Ømm ) // Scale Primary focus (808mm) // 70.14μ/” Schmidt focus (335mm) // 11.6μ/“ Fiber sampling μ,“ /// F#input-F#output 107μ → 1.52” /// F3.9 – F3.74 FRD 90.2μ→ 8” (??) /// F3 - F2.8 FRD Corrector lens and ADC booth neither #N positioner x spectrograph 500 x 10 350 * 1 (??) (inclu. 40 ?? fiducials fixed fibers) Actuator pitch /patrol area 10.4mm / 12mm 15.4 mm / 17.75 mm (AVS NEW)??? Fiber View Camera (FVC) // central IFU Needed // not provided Needed // yes 350 fibers ??, hexagonal Pack. Positioner precision // FVC fiber centroid precision 5μ // <3μ 6.5 μ // <4(??) Schmidt Mayal FVC on Schmidt

Spectrograph Optical Specifications Apart of the two cameras, there is a double parallel pseudo- slit, one for positioner fibers and other for central IFU fibers. parameter DESI CASE Resolution (λ/∆λ) 360 nm < λ< 555 nm: > 1500 555 nm < λ< 656 nm: > 3000 656 nm < λ< 980 nm: > 4000 360 nm < λ< 600 nm: 1500 (????) 600 nm < λ< 950 nm: 3000 (????) Output Fiber diameter, focal # Pseudo-Slit dimension 107μ→ 1.52” , F 3.74 120.9 mm 90.2μ → 8” , F 2.8 FASTER COLIMATOR, 101 mm BUT SMALL PSEUDO SLIT F# mirror collimator , F# camera Demagnification factor, slit on detector F 3.74 , F1.7 2.2 , 54.54mm F 2.8????? , F 1.55 ????TBC 1.7 , 59.1mm NEEDED demag. To this slit=101mm CCD, Pixel detector, side 3 * 4k x 4k , 15μ, 60mm 2 * 4k x 4k , 15μ, 60mm Minimum resolution elements 3 pixels > Nyquist 3 pixels Fiber spacing (slit plane) 230μ to prevent cross talk 193μ Number of fibers (spatial) 500 singles fibers(positioners) Singles fibers (positioners) ??? OR 350 in the central IFU ??? (for a 101mm slit long) Sky + standard star on target selection 40 sky + 10 standard star 20sky (????)+ 5 standard star (????) (CASE FOV is bigger) 217 fibers IFU =2.55mm→3,66’ BLUE Pseudo-slit RED 331 fibers IFU =3.15mm→ 4,5’

Spectrograph Optical Design (DESI) The design considerations to reduce cost of DESI f/1.7 !!! cameras: To minimize: the number of lenses, aspheric surfaces, the volume of glass; use low cost glass with frequent melts. To maximize the throughput the number of lenses was minimized and only glasses with high transmission in the band pass were used. The last lens was fused silica since it is the vacuum seal to the cryostat. The DESI spectrograph use Volume Phase Holographic (VPH). They have the highest throughput over the relatively broad band ∆β <16⁰. The fringes of the gratings are tilted to remove the Littrow ghost. The VPH grating is made by sandwiching a gelatin between two fused silica optical flat plates. ∆β = dispersión angle, 1/σ is the line density, and Ø is the tilt angle. Radius Spot RMS of the three cameras vs. wavelength Resolution vs. Wavelength

Spectrograph Optical Design (CASE) The more important difference with the DESI spectrograph is coming from the focal number of the fiber at the output, that is dependent of the focal number at the input and the Focal Ratio Degradation (FRD) in the figure: For DESI: f input = 3.9 and 40 meters → f out=3.74 For CASE: f input = 3 and 10 meters → f out=2.8??? FAST COLIMATOR AND CAMERA DESIGNS are NEEDED Grims and VPH compatible with CASE, in function of Wavelength range, resolution, etc FINAL RESOLUTIONS AND RANGES CHOICED ARE NEEDED VPH efficiency and wavelength range

Spectrograph general design Booth DESI and CASE, adopt the same solution for the pseudo-slit, just in front of a mirror collimator. But in CASE there is two pseudo-slit parallel and close together, One receives light front the positioners, and the other from the central IFU. A laminar switching mechanism permit to work only one at same time. Another mechanism provide light to retro - illumination of the fiber (by the spectrograph side) and the fiducials at same time. Two pseudo-slits together Mirror collimator for F5 input and 100mm pseudo-slit long. Dimensions (100x310x60mm) DESI 3D model spectrograph :1.5 m wide × 1.4 m deep × 0.5 m height

Calibration System: Lamps, Sky Lines, Stars, CCD Flat Field Illuminator Multiple calibration sources will be used in CASE, including sky lines, stars, continuum and line (arc) lamps, and a CCD flat field illuminator. The spectrograph is mounted on stationary optical bench in a temperature controlled environment, their calibration should remain quite stable. used obtained Calibration lamps illuminate the pupil of the telescope, over a flat field screen mounted inside the dome establish the wavelength and to measure the point-spread-function (PSF) Continuum lamps e.g. quartz iodine halogen illuminate the pupil of the telescope, over a flat field screen mounted inside the dome. to measure the xy trace location of the spectra on the CCDs and to correct for relative fiber-to-fiber throughput variations. Stars Standard stars will be selected as main-sequence F-stars based upon color and magnitude, By comparing the observed standard star spectra with their modeled spectra and photometry. To provide spectro-photometric calibration to the spectra CCD Flat Field Illuminator illuminates the CCD in the spatial direction with a smooth spectrum such that each pixel receives the same wavelength By comparing each pixel to the median of other pixels with the same wavelength. The wavelength-dependent pixel level response is measured. NEED to dismount the pseudo-slit plate. Once per year???

Comparisons. CASE DESI SDSS MUSE Telescope (m); f/# Schmidt 0.8m; f/3 Mayal 4m; f/3.9 SDSS 2.5m; f/5 4th unit VLT 8m; f/15 (582μ/”) Scale FOV 11.6μ/” 8⁰ 70.14μ/” 3⁰ 60μ/” The FOV is sliced in 24 IFU &spectrog 1’x1’ WFM or 7.5”x7.5”NFM Fiber sampling (μ,“) sampling“ 90.2μ?? 7.7” 107μ 1.52” 180μ 3” Each pixel in IFU element = 0.2”x0.2”WFM 0.025”x0.025”NFM Positioner precision 6.5μ RMS <=9μ?? 5μ RMS By hand Slicer Range /arms 360-950 nm VPH? /2arms 360-980 nm VPH /3 arms 350-950nm/2arm 465-930 nm /24 channels sliced Resolution (λ/∆λ) 1500 at λ< 600nm ??? 3000 at λ >600nm ??? 1500; 360 nm < λ< 555 nm 3000; 555 nm < λ< 656 nm 4000; 656 nm < λ< 980 nm 1500 λ <600nm 3000 λ >600nm 1750 at 465nm 3750 at 930nm Slit size Fiber output, f/# Colimator f/# Camera f/# Resol. element 101mm 90.2μ, f/2.8 ? f/2.8 ? to reach given f/1.55 ? fibers –resol. 48μ 120.9mm 107μ, f/3.74 f/3.74 f/1.7 125mm 180μ, f/4 f/4 f/1.5 67.6μ 24 channels * 48 15” x 0,2” mini slits slice (spatial resolution) 15μ=(0.3-0.4)”WFM;(0.03-0.05)”NFM CCD 2 * 4k x 4k , 15μ 15 * 4k x 4k , 15μ 2k x 2k, 24μ 24 * 4k x 4k, 15μ Fibers, Elements 350 positioner or 350 IFU 10 * 500 320 90000 spectra at same time Pixel / elem. resol. 3 1 If CASE can use a 6k x 6k, 15 CCD, for all the range, with only a Grating, the expected resolution would decrease to 1000-1200 (more calculi are needed).

Conclusions and work to do, for previous optical design Some Telescope parameters are not known in details: no opto-mechanic drawings We need to decide specifications to the spectrograph system: Sky sampling → fiber diameter → number of fibers on ??? Range and resolution/resolutions, single/multiple grating??? Estimation of the FRD for this application, bend, path across telescope, distance??? Collimator and camera focal f/# and its focal distances, to appropriate demagnification ??? etc… Thank you