Triplespec: Motivations and Design. John Wilson

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1 Triplespec: Motivations and Design John Wilson

2 Slit Viewer Prisms Slit Collimator Reimager OAP #2 Window Spec Camera Tele Focus Reimager OAP #2 Grating

3 Outline Scientific Rationale Heritage of Triplespec project Partner Institutions (Cornell, JPL, Caltech) Near Duplicates Spectrographs (Palomar, Keck, APO) Design Considerations & Steps

4 Scientific Rationale Triage instrument for efficient NIR spectral follow-up of survey objects (e.g. Spitzer) General Purpose Facility Spectrograph

5 What science can it address? Any project that requires moderate resolution NIR spectroscopy, but it will excel at Identifying objects discovered in surveys (e.g. Spitzer, CHANDRA, 2MASS) Especially Red objects with no visual counterpart such as Spitzer (NASA) Brown Dwarfs NIRSPEC (R~2000) at Keck, 6 grating settings McLean et al. 2003

6 What science can it address? Any project that requires moderate resolution NIR spectroscopy, but it will excel at Identifying objects discovered in surveys (e.g. Spitzer, CHANDRA, 2MASS) Especially Red objects with no visual counterpart such as Spitzer (NASA) High z objects ESI at Keck Balcells, 2003, RevMexAA Conf Series Becker, Fan, White et al. 2001

7 What science can it address? Any project that requires moderate resolution NIR spectroscopy, but it will excel at Identifying objects discovered in surveys (e.g. Spitzer, CHANDRA, 2MASS) Especially Red objects with no visual counterpart such as Spitzer (NASA) Active Galaxies Palomar long-slit infrared spectrograph, R~1000, 3 grating settings Murphy et al 2001 NOAO/E.J. Schreier(STSci)/NASA

8 Scientific Rationale What enables efficiency? Sufficient resolution to avoid airglow effects µm all-at-once Sufficient slit length for nodding point sources Separate NIR slit viewing channel Minimal Moving Parts (only slit mechanism to choose between two slits)

9 Scientific Rationale Resolution to avoid airglow effects, but not too much so avoid being Read Noise limited Martini & DePoy, SPIE, 2000 Martini & DePoy, SPIE, 2000

10 Scientific Rationale

11 Heritage CorMASS (R=300) Triplespec (R=3600) 2048 pix 256 pix 1024 pix 256 pix Wolf-Rayet in Spectrograph 35 dia FOV 4 Jupiter and Satellite in Slit Viewer Palomar 60-inch (13 at APO) slit 4

12 Slit Length Considerations 15 arcsec Solar (sunrise) 0.65 μm Science Object 6 arcsec z J Airglow Thermal (sky) 2.5 μm 2 arcsec K H CorMASS

13 Multiple-Partners Copy 1: Palomar 200-inch Facility Instrument Cornell + JPL Copy 2: Keck 10-meter Facility Instrument Caltech Caltech Copy 3: APO 3.5 meter Facility Instrument UVA Keck Image 2000 WELDON OWEN INC.

14 Multiple-Partners Instruments are cheaper by the dozen, but usually we just build one Share knowledge / expertise Efficient use of collaboration labor Maximize chance of success Share lessons learned during commissioning Copy Commissioning Palomar Summer 06 Keck Summer 06 APO Winter APO copy benefits from lessons learned of first two

15 Same instruments used at such different telescopes? Tailor re-imager to transfer telescope f/# to common f/10.67 Dewar tolerant of various telescope mountings Aperture (m) Mount Re-imager Spec Plate Scale (arcsec/pix) Slit Width (arcsec) Ks Median Seeing (arcsec) Palomar 5 Cass f/16 -> f/ (2.7 pix sampling) 1.2 Keck 10 Bent- Cass f/16 -> f/ (2.7 pix sampling) APO 3.5 Nasmyth f/10.4 -> f/ (2.1 pix sampling, Resolution ~3600) 1.43 (2.7 pix sampling, Resolution ~2700)

16 Optical Design Considerations Meet Science Requirements Design in sections (Reimager, Collimator, Disperser, Camera) Minimize Optical Elements (throughput) Maximize use of reflective optics (chromatism, warm-cold placement) Package Efficiently: Opto-Mechanical Accommodate Back Focal Distances of Telescope(s) Provide cold Lyot Stop (spectral range includes K-band) Minimize $$ for optics Minimize Stray Light (placement of optics) Provide FOV for Slit Viewer

17 Optical Design: Step 1 Strawman Dispersive Section Wavelength Coverage: micron Cannot use grating as cross-disperser since > factor of 2 wavelength span prism Chose grating to give wavelength coverage while minimizing number of orders (preserve slit length) Knew from CorMASS work the type of crossdispersing prisms I would need to give balanced cross-dispersion across wavelength

Relay Collimator fairly simple: Need one Off-axis paraboloid

18 Optical Design: Step 2 Strawman Reimager & Collimator Two options for reimager: Pair of Off-axis paraboloids Offner Relay Collimator fairly simple: Need one Off-axis paraboloid with long enough focal length to produce spot size necessary on grating

19 Optical Design: Step 3 Start talking with optics vendors about choices to firm up design, quote requests Start working with mechanical engineer to package optics inside cryogenic dewar

20 Work in Progress Phase Older Design (Offner & Double-Pass Prism)

21 Work in Progress Phase Older Design (Two OAP s & Prisms in Series)

22 Work in Progress Phase Close to Final Design (as seen from telescope)

23 Work in Progress Phase Final Design (as seen from telescope)

24 Early order Layout Work in Progress Phase

25 Final Optical Design 2048 pix 1024 pix

26 Re-imaging Section Dewar Window Telescope Focus Off Axis Paraboloid 1 Off Axis Paraboloid 2 Reflective Slit Lyot Stop

27 Re-imaging Design for APO 40 mm APO Tele Focus Working to keep Slit for both designs in same place APO Slit Palomar Tele Focus Palomar Slit

28 Collimation & Folds Dewar Window Telescope Focus Reflective Slit Fold Mirror 1 Fold Mirror 2 Collimator (Off Axis Paraboloid)

29 Re-imaging Section Dewar Window Off Axis Paraboloid 1 Off Axis Paraboloid 2 Fold Mirror 1 Fold Mirror 2 Collimator (Off Axis Paraboloid)

30 Cross-Dispersing Prisms (2) ZnSe + (1) Infrasil Spectrograph Fold Mirror 2 Reflection Grating (110.5 l/mm, 22 deg blaze) 7-element Refractive Camera Detector (2 quadrant HAWAII-II)

31 Slit Viewer Reflective Slit Detector (HAWAII-I) Fold Mirror Lens 1 (ZnS, aspheric) Lyot Stop + Ks Filter Lens 2 (ZnS, aspheric)

32 Mechanical Design Considerations Mechanical Design Efficient Packaging: Reduce Weight, Reduce Croyogen Usage, Increase Holdtime (desire > 24 hrs min) Multiple Telescope Use: Spillage Back Focal Distance Minimize Flexure of Instrument Minimize Stray Light

33 Dewar: LN2 Tank Design Novel Crescent shaped design Minimize Overall Dewar Size Accommodate variety of telescope mounting positions (Cass, Bent Cass, Nasmyth) 2-day hold time for half-fill (60 l)

34 Cold Volume: Bulkhead System Bulkheads 1 & 5: Connect Vacuum Shell to Cold Volume Bulkheads 2 4: Optical Bench Allow Alignment / Assembly external to dewar System of spreaders will couple bulkheads

35 Cold Volume: Bulkhead System

Thermal Design Sensitivity of CaF 2 to thermal shock High thermal expansion coefficient and low conduction coefficient. Set a maximum allowable stress of 7,000 Mpa at lens cell interface (ael 36.

36 Thermal Design Sensitivity of CaF 2 to thermal shock High thermal expansion coefficient and low conduction coefficient. Set a maximum allowable stress of 7,000 Mpa at lens cell interface (ael 36.5 Gpa) Max rate of heat extraction at lens cell interface of 4,000 W/m 2. Max cool down rate of 0.30 K /min. Assistance from NOAO NEWFIRM documentation and discussions w/ Ron Probst (NOAO) 4,000 W/m 2 max

37 Lens Retention Axial Lens Retention -Canted coil springs retain optics ~2.2 lb/in at circumference Delrin spacers distribute loads Radial Lens Retention - 3 Point Fit to 6061-T6 housing MMC (min clearance).001 decenter LMC (max clearance) point radial contact to athermalized delrin pins (Adjusted to Fit ) Ref. Relief Zone

38 Crack Tests at Axsys Cornell & Caltech cameras complete, successfully tested OFHC Shorts (typ of 3) Test Dewar G-10 CR Pre-load w/ 30 Belleville Washers (typ of 3)

39 0 Rate of Temp Change adjacent to CaF Thermal Design Measured peak temp change of 0.5 K / min v. design goal of 0.3 K / min Temp Change (K/min) Cool Down #2 temp change prediction Temp (K) Time (sec) midcam coldplate coldring shield prediction 40 hrs to cool lenses met model prediction Time (hrs)

Optical/NIR Spectroscopy A3130. John Wilson Univ of Virginia

Optical/NIR Spectroscopy A3130 John Wilson Univ of Virginia Topics: Photometry is low resolution spectroscopy Uses of spectroscopy in astronomy Data cubes and dimensionality challenge Spectrograph design