1. FMOS: the fiber multiple-object spectrograph IV current status of OHS-based spectrograph Kyoto University : F.Iwamuro, T.Maihara, K.Ohta, S.Eto, M.Sakai NAOJ : M.Akiyama, M.Kimura, N.Tamura, J.Noumaru, H.Karoji University of Oxford / RAL : G.B.Dolton, I.J.Lewis / I.A.J.Tosh University of Durham : G.J.Murray, N.A.Dipper, D.J.Robertoson AAO : P.R.Gillingham, S.Smedley, G.A.Smith, G.Frost FMOS is the next common-use instrument of the Subaru Telescope developed by

2. Specification of FMOS.400 targets multiplicity Near-infrared 0.9-1.8μm wavelength range Field coverage of 30' diameter.OH suppression capability Spectral resolition : 2200 or 500 Expected limiting magnitude : J ～ 22mag H ～ 20.5mag

3. Components of FMOS Prime focus unit Corrector lenses / Echidna (AAO) Instrument-bay (Kyoto) Fiber bundle unit Fiber connector box + Two fiber slits (Durham) Infrared spectrographs IRS1 (Kyoto) IRS2 (oxford / RAL)

4. Optical Layout of IRS1 Mosaic grating Off-axis Schmidt plate Mask mirror Fiber slit Special Schmidt plate Fiber bundle 1.4m Camera mirror Camera cryostat Camera lens system Thermal cut-off filter Entrance window VPH grating Folding mirror

5. Optical Layout of IRS1 Mosaic grating Off-axis Schmidt plate Mask mirror Fiber slit Special Schmidt plate Fiber bundle 1.4m Camera mirror Camera cryostat Camera lens system Thermal cut-off filter Entrance window VPH grating Folding mirror Primary Pupil Primary Spectra Secondary Pupil Secondary Spectra

6. Observation Mode Low resolution mode R=500 / Full wavelength range High resolution mode R=2200 / Quarter of the wavelength range VPH grating reduces the dispersion given by the first grating.

7. Test Fiber Bundle 247 fibers, 200μmφcore Slit length of 12cm (having a fan shape along the curvature of the focal sphere of the Schmidt optical system of IRS1.) 3.3mm x 3.4mm IFU-type aperture

8. Schmidt Plates Off-axis Schmidt plate (280mm x 236mm) Manufactured by NAGASE INTEGREX Co.,Ltd. using high-accuracy grinding processing. Shape accuracy of 0.3μm, roughness of 80nm rms. Special Schmidt plate (315mm x 251mm) Combination of concave-flat and flat-convex elements. Manufactured by RIKEN using “ELID” (ELectrolytic In-process Dressing) grinding method. Shape accuracy of 3μm, roughness of 100nm rms.

9. Refrigerator 2.3m(w) x 2.9m(l) x 2.4m(h), 20cm(t) wall T min < -50 ℃ (Controled by PC) 19 (temperature) + 1 (humidity) sensors Dry air (d.p.< -60 ℃ ) supplied through the membrane air dryer

10. Camera Cryostat 61cmφ x 128cm (weight of ～ 350kg) 25cmφ window 5 spherical lenses HAWAII-2 2k 2 array Thermal cut-off filter Circular-arc guiding stage Bellows + slidable flange

11. Optical Bench Frame Aluminum frames contract ～ 1mm as it cools down

12. Slit / Mask Mirror Adjustment Cancel the frame contraction. Adjust the focus on the mask mirror. 6-axis adjustable stage with Picomotor TM actuators 6 rotary potentiometers Low-temp. grease + Heater

13. Mosaic Grating 8 Picomotor TM actuators Low-temperature grease + Heater

14. Cooling Test Camera cryostat : 4K/hour →200K/50hours Refrigerator : ～ 1K/hour → 50K/50hours (The operation parameter has not been fixed yet owing to the compressor replacement.) 77K 1day 273K 0℃0℃ - 40 ℃ 1day - 50 ℃ 2days

15. Mosaic Grating Adjustment Correct a small distortion of the grating holder at low temperature. 1.3μm Infrared laser (with many sub-peaks!) Size ～ 4pixφ (3.5pixφ real image + 2pix optical aberration) G1 G2 G3 G4 Sub-peaks of the laser Leaked light into the nearest fibers Cool Down Readjust Fiber slit image Single fiber image

16. Focus Adjustment Fiber and Mask images must be focused simultaneously (by moving slit, mask mirror, and detector). Determine the focal position and the tilt angle of the detector (in each observation mode). Enlarged ViewBefore tilt adjustmentAfter tilt adjustment Fiber image Mask image

17. Summary IRS1 has been installed in the new floor of the Subaru telescope. The optical performance is consistent with the expected value. The temperature of the optics was reached -50 ℃ without fine tuning of the refrigerate system.  Adjustment at the lowest temperature  Improvement of the airglow mask  Handling of the ghost images  Complete shielding of the infrared stray light Remaining Items