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

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

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)

Optical Layout of IRS1

Mosaic grating

Off-axis Schmidt plate

Mask mirror

Fiber slit

Special Schmidt plate

Fiber bundle

1.4m Cameramirror

Camera cryostat

Camera lens system

Thermal cut-off filter

Entrance window

VPH grating

Folding mirror

Optical Layout of IRS1

Mosaic grating

Off-axis Schmidt plate

Mask mirror

Fiber slit

Special Schmidt plate

Fiber bundle

1.4m Cameramirror

Camera cryostat

Camera lens system

Thermal cut-off filter

Entrance window

VPH grating

Folding mirror

Primary Pupil Primary Spectra

Secondary Pupil

Secondary Spectra

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.

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

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.

Refrigerator

• 2.3m(w) x 2.9m(l) x 2.4m(h), 20cm(t) wall

• Tmin < -50℃ (Controled by PC)

• 19 (temperature) +

1 (humidity) sensors

• Dry air (d.p.< -60 )℃ supplied through the

membrane air dryer

Camera Cryostat

• 61cmφ x 128cm (weight of ～ 350kg)• 25cmφwindow

• 5 spherical lenses

• HAWAII-2 2k2 array

• Thermal cut-off filter

• Circular-arc

guiding stage

• Bellows

+ slidable flange

Optical Bench Frame

• Aluminum frames contract ～ 1mm as it cools down

Slit / Mask Mirror Adjustment

• Cancel the frame contraction.

• Adjust the focus on the mask mirror.• 6-axis adjustable stage

with PicomotorTM actuators

• 6 rotary potentiometers

• Low-temp. grease + Heater

Mosaic Grating

• 8 PicomotorTM actuators

• Low-temperature grease + Heater

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℃

- 40℃

1day

- 50℃

2days

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)

G1G2

G3G4 Sub-peaks

of the laser

Leaked light into the nearest fibers

CoolDown

Readjust

Fiber slit imageSingle fiber imageSingle fiber image

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 View Before tilt adjustment After tilt adjustment

Fiberimage

Maskimage

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