-- InfraRed Doppler for the Subaru telescope --

IRD is an infrared high-dispersion fiber-fed spectrometer which covers the wavelength range from 0.97 to 1.75 microns with a maximum 70,000 spectral resolution. The instrument has a fiber injection module for star-light and laser frequency comb light injection into fibers on the Nasmith platform after wavefront correction by the adaptive system, AO188. The spectrometer design incorporates a high-blaze angle Echelle grating, collimator mirrors, a cross disperser grating and a camera lens system, and two 2D array detectors. These are all enclosed in a vacuum chamber and are cooled to ~ 180K (optics) and 80K (detector) for thermal background and dark noise reduction. The vacuum chamber is placed in the coude room of the Subaru to ensure a stable temperature environment. The laser frequency comb for IRD is developed based on a novel multi-gigahertz spaced comb generation technology employing a frequency stabilized laser diode, an optical pulse synthesizer and a highly nonlinear fiber.
Spectral resolution ~70,000 max See also here
Wavelength coverage0.97-1.75um
Fiber diameter0.48 arcsec
Wavelength calibratorsLaser frequency comb, ThAr lamp, UrNe lamp
Flat calibrationWhite lamp at NIR-Nas
ThroughputCheck here
Saturation level30,000 ADU (10% linearity error)
Temperature stability+/- 35mK for 10 days (optics) +/-30mK (Detector)
Sensitivity 1111 sec at 999nm and 400 sec at 1620nm to acheive S/N=100 for dwarf stars with Teff=3000K and J-mag=10
769 sec at 999nm and 417 sec at 1620nm to acheive S/N=100 for dwarf stars with Teff=5500K and J-mag=10
DetectorsHAWAII2 RG x 2
Gain2.85 e-/ADU at YJ-band detector
2.60 e-/ADU at H-band detector
At the this stage, the gain measurements may have an uncertainty comparable to about +/- 0.2.
Dark current< ~0.01 e-/s for YJ-band and H-band detectors
Read-out noise~12e-(10min. exposure)
Linearity 10% linearity error at 30,000 ADU
FIM acquisition CCD pixel scale 0.067 arcsec/pixel
Optics wavelength coverage 0.97-1.75um
Fiber FOV 0".48
FIM acquisition CCD camera limiting magnitude J = 18.8 (S/N=10, DIT=10sec, in case of a star not injected into a fiber)
J=14.9 (S/N=10, DIT=60sec, in case of a star light injected in to a fiber)
If you want to achieve high instrumental RV stability (~3m/s), we recommend that a target J mag<13 for a good image centering against a fiber core.
FIM acquisition CCD camera wavelength coverage0.97-1.1 um
FIM acquisition CCD camera FOV 30
Requirement for a AO guide starif a star R' mag <13, a coupling efficiency into a fiber will be around 60% (R'=R-2.5log10(0.43*(R-I)^2-0.38*(R-I)+1.0).See also here
Wavelength coverage 1040-1750nm
Mode spacing 12.5GHz
Frequnecy stability 0.03MHz (Standard deviation) for 140 hrs
Intensity stability 0.7dB
Additional componetsSpectrum shaper, Depolarizer, Mode scramber
MethodSimultaneous wavelength reference
Fiber Two multi-mode fibers
Calibration sourcesLaser comb, ThAr Hollow Cathode Lamp, UrNe lamp
Scramblers Various (not necessary for users to specify)
RV instrument stability ~3 m/s (the goal is 1m/s, the stability demonstration is still ongoing for further improvement. Shared-risk operation in S2018B)
Min. exposure time1.5 sec.
Typical overhead time<600 sec.(if your target is faint, overhead will be increased)
Sensitivity calculationCheck this page
Data reductionto be updated

Contact mail address

Motohide Tamura, Takayuki Kotani (send mail to ird_tech (at) ird.mtk.nao.ac.jp)