Radio observations ・ ~100 species have been detected

1. Cryostat Collimator (F/20, f80) L Si:As 512*412 4K L n Slit viewer Echelle grating Groove interval : 0.6 mm Blaze angle : 68.75 deg. Order : 344 – 560 Size : 30×30×72 mm Echelle grating Groove interval : 0.6 mm Blaze angle : 68.75 deg. Order : 344 – 560 Size : 30×30×72 mm DL=2nL DL=2L InSb 256*256 Immersion grating Conventional grating 1140 mmf×1145 mm H Camera lens (F/7.7) Slit mirror 30K Cross disperser Immersion Grating Diameter: 800 mm 10.882 mm 10.890 mm NK=1010(s)-1010(a) : 10.8859 mm on m= 403rd (10.877 –10.911 mm). Dn(FWHM) ~ 7 pixels (0.047 cm-1). Spectral Resolution: ~21,000 (focus re-adjustment under way) Integration : 15 sec Nphoton(NH3) : 105 molecules/sec Colour gradation indicates magnitude of transmittance (Brighter pixel point corresponds to higher transmittance). Wavelength : 10.27 - 10.99 mm. Mid-Infrared High-Dispersion Molecular Spectroscopy using Ge Immersion Grating Spectrograph (IRHS) Y. Hirahara1 , T. Hirao1, T. N. Oka1, Y. Kakeue1, H. Tokoro2, N. Ebizuka3, K. Kawaguchi4, T. Masuda51Grad. School of Environ. Studies, Nagoya University, 2Nano-Opt Institute, 3Faculty of Science, Nagoya University, 4Faculty of Science, Okayama University, 5Instrument Development Centre, Nagoya University Studies of Interstellar Molecules & Chemistry IR High Resolution Observations Only a few observations were reported so far … - Orion KL, 4-25 mm, IRTF (3.0 m) & IRSHELL, R = l/Dl = 25,000 (Evans et al. 1991) - IRC+10216, 8-13 mm, Kitt Peak Mayall telescope (4 m) & FTS, R = 100,000 (Keady & Ridgway 1993, Boyle et al. 1994) More than 130 molecules have been identified through radio, infrared (IR) and visible spectral observations. The key species without dipole moment have not been detected yet! 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) e.g. CH3+,c-C3H3+ Detectable only thru IR observation !! The chemistry of dense cloud ・Low sensitivity (S/N = 20, 143 min.) : Observable a few objects CH3+ c-C3H3+ ・Dominant noise source is black body radiation in mid-Infrared region ￫FTS (Fourier-transform spectrometer) is no longer effective A key species, H3+,has been detected using infrared high resolution spectroscopy (T.R.Geballe& T.Oka,1996) (Boyle et al., 1994) • High sensitive and resolution grating spectrometer is needed • IR observation needed for detailed analysis IRHS (mid-InfraRed High dispersion Spectrograph) ; R = 40,000 @ 10 mm 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 mm) : The resolving power R = 40,000 ・A broad band width : ~1 mm 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 Optics of IRHS Germanium Immersion Grating 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. ・ Directly grooved onto high refractive index material (Refractive index ‘n’ of Germanium : 4 @ 7-14 mm) ・ Increases the resolving power by n-times ・Reduces the size and the weight for the instrument R=DL/l Spectrometer optics Fore-optics Echelle format The Ge immersion grating has been fabricated by “ RIKEN” using ELID (ELectrolytic In process Dressing) micro-machining method. Focal Plane Array Detector 8 cross disperser rotational positions provide full coverage of 7.5-13.5 mm 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. • Slit width 0.612 arcsec (0.488 mm) at R = 50,000 • Echelle grating Ge immersion grating • Groove interval : 0.6 mm • Blaze angle : 68.75 deg. • Order : 344-560 • Cross Disperser Short wavelength (7.5-10 mm) • Groove constant : 100 grooves/mm • Blaze angle : 26.7 deg. • Long wavelength (10-13.5 mm) • 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 mm/pixel • Slit viewer • InSb • 256×256 pixels, ~30 mm /pixel Si:As IBC(Impurity-Band Conductor) Absorption Spectra of NH3 (n2) Emission Spectra of NH3 (n2)@300 ºC NH3 Q(10, 10)a: 10.8859 mm (918.621 cm-1 ) Liq. N2 Baffle Lens (F12.5) IRHS NH3n2 mode (+ inversion) Light Source: Glower Cell Length:11cm Saturation Time:0.83s “net” Tinteg : 3.32sec Dn(FWHM) ~8 pixels (0.053 cm-1). ~pressure broadened N(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) NH3 Cell (1 Torr, 300 ºC, L=11 cm, f3.6 cm) “Radiation Shield” (an Al Can, ~ 0 ºC)