Radio observations ・ ~100 species have been detected
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Transcript of Radio observations ・ ~100 species have been detected
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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 )