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10.27-10.99 μmregion(910 - 974 cm-1)

Spectrographrecordedby IRHS

407th408th409th410th411st412nd413rd414th415th416th417th418th419th420th421st422nd423rd424th425th

406th

398th399th400th401st402nd403rd404th405th

P(20)P(18) P(16)

P(20)

10.55140μm10.57105μm

10.59104μm

CO2 (ν1, ν2l, ν3)=(0, 00, 1) - (1, 00, 0)

AbsorptionofNH3 ν2 band

Radio observations ・ ~100 species have been detected ・ High spectral sensitivity and resolution

Infrared observations ・ Only ~30 species have been detected ・ Molecules without dipole moment ・ Precise analysis (T, N, VLSR ・・・ )　　　　　 with rovibrational spectra

・ Low spectral sensitivity and resolution Molecules detected by IR observations H2O, CO, HF, SiO, OH, H2, C2H2, CS, CH4, NH3, HCN, C2H4, CH, NH, HCl, SiH4, C2H, C3, C5, CN, OCS, SiS, H3

+, SH, CO2, SO2, CH3, HC3N, HC5N, C4H2, C6H2, C6H6, CH3C2H, CH3C4H　 (Nonpolar species)

(Boyle et al., 1994)

Optics of IRHS

IR High Resolution Observations

High sensitive and resolution grating spectrometer is needed

IRHS (mid-InfraRed High dispersion Spectrograph) ; R = 40,000 @ 10 μm

Germanium Immersion Grating

8 cross disperser rotational positions provide full coverage of 7.5-13.5 μm

Studies of Interstellar Molecules & Chemistry

IRHS(Mid-InfraRed High dispersion Spectrograph )

・ A cryogenic cross-dispersed echelle spectrometer using Ge immersion grating・ A high spectral resolution in N-Band (7.5~13.5 μm) : The resolving power R 40,000・ A broad band width : ~1 μm per a rotational angle of cross-disperser・ A High sensitivity : 1Jy = 10-26 W m-2 Hz-1 (exp. time ~100 sec., S/N =10)・ For IR Nasmyth focus of NAOJ SUBARU 8.2 m telescope

Cryostat

1140 mm×1145 mm H

Echelle format

Only a few observations were reported so far …

- Orion KL, 4-25 μm, IRTF (3.0 m) & IRSHELL, R = = 25,000 (Evans et al. 1991)

- IRC+10216, 8-13 μm, Kitt Peak Mayall telescope (4 m) & FTS, R = 100,000 (Keady & Ridgway 1993, Boyle et al. 1994)

・ Low sensitivity (S/N = 20, 143 min.) 　　　　 : Observable a few objects

￫ FTS (Fourier-transform spectrometer) is no longer effective

• IR observation needed for detailed analysis

The chemistry of dense cloud

The key species without dipole moment have not been detected yet!

e.g. CH3+, c-C3H3

+

Detectable only thru IR observation !!

A key species, H3+, has been detected using in

frared high resolution spectroscopy (T.R.Geballe& T.Oka,1996)

CH3+ c-C3H3

+

Echelle gratingGroove interval : 0.6 mmBlaze angle : 68.75 deg.

Order : 344 – 560Size : 30×30×72 mm

Echelle gratingGroove interval : 0.6 mmBlaze angle : 68.75 deg.

Order : 344 – 560Size : 30×30×72 mm

L

n

Immersion grating

L=2nL

L

L=2L

Conventional grating

・ Directly grooved onto high refractive index material (Refractive index ‘n’ of Germanium : 4 @ 7-14 μm )・ Increases the resolving power by n-times ・ Reduces the size and the weight for the instrument 　　

The Ge immersion grating has been fabricated by “ RIKEN” using ELID (ELectrolytic In process Dressing) micro-machining method. 　　　　

The optics consists of two sections: the fore-optics and the spectrometer optics. The fore-optics designed for IR Nasmyth focus of NAOJ,SUBARU (F/12.5) images the telescope focal plane with magnifying power of 1.6 onto a slit mirror. The image reflected by the slit mirror goes into slit viewer, which images the objects onto InSb detector array. The spectrometer optics contains the Ge immersion echelle grating, the cross disperser, their collimator mirrors, the camera lenses and the Si:As IBC (Impurity Band Conductor) detector array. To reduce thermal radiation of the instrument, all optics of IRHS is arranged on the cold optical base plate (~30 K) of the cryostat with the diameter of 80 cm.

• Slit width 0.612 arcsec (0.488 mm) at R = 50,000• Echelle grating Ge immersion grating

Groove interval : 0.6 mmBlaze angle : 68.75 deg.Order : 344-560

• Cross Disperser Short wavelength (7.5-10 μm)Groove constant : 100 grooves/mm

Blaze angle : 26.7 deg. Long wavelength (10-13.5 μm) Groove constant : 61.97 grooves/mm Blaze angle : 18.1 deg.

• Collimator Al spherical mirror Focal length : 500 mm (F/20)• Camera Ge and ZnSe lenses Focal length : 192.5 mm (F/7.7)• Detector Spectrometer Si:As IBC 512×412 pixels, 30 μm/pixel Slit viewer InSb 256×256 pixels, 30 μm /pixel

Focal Plane Array Detector

IRHS has been employed two focal plane array detector. One of InSb with 256*256 pixels for slit viewer optics, and the other is Si:As IBC with 412*512 pixels for spectrometer optics manufactured by Raytheon Co. USA.

Si:As IBC InSb

Array configurationPixel size

Array active areaWavelength range

Operating temperatureWell sizeQuantum

efficiencyDark currentReadout noise

512×412 pixels30×30 µm

15.4×12.4 mm1–28 µm

4 K~1×105 electrons

> 45 %< 1 electron/s20 electrons

256×256 pixels30×30 µm7.7×7.7 mm0.9–5 µm

35 K~2×105 electrons

> 80 %< 1 electron/s25 electrons

Si:As IBC(Impurity-Band Conductor)

More than 130 molecules have been identified through radio, infrared (IR) and visible spectral observations.

Immersion Grating

30K

Camera lens (F/7.7)

Slit viewer

Si:As512*412

4K

Diameter: 800 mm

Collimator (F/20, 80)

Cross disperser

Slit mirror

InSb256*256Spectrometer opticsSpectrometer optics

Fore-opticsFore-optics

R=L/

ν(FWHM) ~8 pixels (0.053 cm-1). ~pressure broadenedN(NH3)=3 x 1018 cm-2

High S/N: ~20 for absorbance=1% in 0.166 sec. integration

(cf: ~30 secs required for the same S/N using FT-IR & MCT detector)

Mid-Infrared High-Dispersion Molecular Spectroscopy using Mid-Infrared High-Dispersion Molecular Spectroscopy using Ge Immersion Grating Spectrograph (IRHS)Ge Immersion Grating Spectrograph (IRHS)

Y. Hirahara1 , T. Hirao1, T. N. Oka1, Y. Kakeue1, H. Tokoro2, N. Ebizuka3, K. Kawaguchi4, T. Masuda5 1Grad. School of Environ. Studies, Nagoya University, 2Nano-Opt Institute, 3Faculty of Science, Nagoya

University, 4Faculty of Science, Okayama University, 5Instrument Development Centre, Nagoya University

・ Dominant noise source is black body radiation in mid-Infrared region

Emission Spectra of NH3 (ν2)@300 ºC

Colour gradation indicates magnitude of transmittance(Brighter pixel point corresponds to higher transmittance).Wavelength : 10.27 - 10.99 μm.

10.882 μm 10.890 μm

NK=1010(s)-1010(a) : 10.8859 μm on m= 403rd (10.877 –10.911 μm).

ν(FWHM) ~ 7 pixels (0.047 cm-1).Spectral Resolution: ~21,000(focus re-adjustment under way)

Integration : 15 sec

Nphoton(NH3) : 105 molecules/sec

IRHS

Liq. N2 Baffle

NH3 Cell

(1 Torr, 300 ºC, L=11 cm, 3.6 cm)

Lens (F12.5)

“Radiation Shield” (an Al Can, ~ 0 ºC)

Light Source: GlowerCell Length:11cm Saturation Time:0.83s“net” Tinteg : 3.32sec

Absorption Spectra of NH3 (ν2)

NH3 ν2 mode(+

inversion)

NH3 Q(10, 10)a: 10.8859 μm (918.621 cm-1 )