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FMOS: the fiber multiple-object spectrograph IV
current status of OHS-based spectrograph
FMOS is the next common-use instrument
of the Subaru Telescope developed by
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
Specification of FMOS
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.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
Folding mirror
Off-axis Schmidt plate
VPH grating
Entrance window
Thermal cut-off filter
Camera lens system
Camera cryostat
Fiber bundle
Mask mirror
Fiber slit
Special Schmidt plate
1.4m Camera
mirror
Optical Layout of IRS1
Primary Pupil
Folding mirror
Mosaic grating
Primary Spectra
Off-axis Schmidt plate
VPH grating
Entrance window
Thermal cut-off filter
Secondary Spectra
Camera lens system
Camera cryostat
Fiber bundle
Secondary Pupil
Mask mirror
Fiber slit
Special Schmidt plate
1.4m Camera
mirror
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
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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
2days
(The operation parameter has not been fixed yet owing to the compressor replacement.)
273K
1day
0℃
- 50℃
77K
- 40℃
1day
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
G3
G2
G4
Single fiber image
Cool
Down
Readjust
Leaked light into
the nearest fibers
Sub-peaks
of the laser
Single fiber image
Fiber slit 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).
Fiber
image
Mask
image
Enlarged View
Before tilt adjustment
After tilt adjustment
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.
Remaining Items
 Adjustment at the lowest temperature
 Improvement of the airglow mask
 Handling of the ghost images
 Complete shielding of the infrared stray light