Please visit the REACH web cite if you would like to use REACH.
IRD is an infrared high-dispersion fiber-fed spectrometer that covers the wavelengths from 0.97 to 1.75 microns with a maximum spectral resolution of 70,000. The wavelength calibration of IRD can be performed using a laser frequency comb (LFC), simulteniously measured with an object spectrum. Star- and LFC-lights are injected into fibers via a fiber injection module on the Nasmyth platform. Before the star-light is injected into fibers, its wavefront is corrected by the adaptive optics system, AO188. The spectrometer design incorporates a high-blaze angle Echelle grating, collimator mirrors, a cross disperser grating, a camera lens system, and two 2D array detectors. These are all enclosed in a vacuum chamber and are cooled to ~ 180 K (optics) and 80 K (detector), allowing for thermal-background and dark-noise reduction. The vacuum chamber is placed in the coude room of the Subaru Telescope to stabilize the temperature environment of IRD. The IRD's LFC system implements the multi-gigahertz spaced comb generation technology that consists of a frequency stabilized laser diode, an optical pulse synthesizer, and a highly nonlinear fiber.
The new Laser Guide Star (LGS) system can be used together with IRD to improve a sensitivity for a faint star in the visible. The figure and table below show the fiber injection efficiency obtained with the new LGS for 3 on-axis tip-tilt guide stars, designated by the red rectangular. Please refer to the sensitivity section to estimate the required exposure time by taking into account the fiber injection efficiency. Please note that the at least 10 minute overhead time is required for target acquisition with the IRD FIM camera and injection of target light to a fiber, in addition to the overhead for the LGS.
Notice for IRD Observation:
1. SSP-Observations: IRD SSP has been started from S19A. Any proposal using IRD should clarify how its scientific aim is different from that of SSP, because doing similar science as aimed in SSP is not allowed. The SSP target list will not be open to the public, so please consult the IRD team well before submitting your proposal.
2. Time Exchange: Observations allocated on IRD can be swapped with other proposals which will use IRD. The time-swapping between your and IRD-SSP program is also possible. If you want to swap with other instruments (e.g., SCExAO), please, well in advance, consult us to discuss its feasibility.
By two weeks before the observing date, please let us know (e-mail address is below) the time-swapping plan.
Contact mail address for time swapping : ird_time_swap (at) ird.mtk.nao.ac.jp
General contact mail address: ird_tech_at_ml.nao.ac.jp
| Spectral resolution | ~70,000 max See also here |
| Wavelength coverage | 0.97-1.75 um |
| Fiber diameter | 0.48 arcsec |
| Wavelength calibrators | Laser frequency comb, ThAr lamp, UrNe lamp |
| Flat calibration | White lamp at NIR-Nas |
| Throughput | Check here |
| Saturation level | 30,000 ADU (10% linearity error) |
| Temperature stability | +/- 35 mK for 10 days (optics) +/-30 mK (Detector) |
| Sensitivity | Check this page |
| Sensitivity gain with LGS for fainter stars | The use of the laser guide star (LGS) for AO188 will improve a fiber injection efficiency, if your target is very faint in the visible. From our engineering test, we found that a fiber injection efficiency was improved from 10% to 20% for R=15.2, I = 12.75 mag star (= R' mag is 14.1, see this figure ) in ~1".0 seeing condition. Please note that predicting the gain of the LGS mode for a different seeing condition and different brightness of a star is not easy because of a lack of actual observing data. In addition, the LGS mode requires large overhead, at least 15 minutes for AO adjustments. Please see the AO188 web page for more details. |
| Detectors | HAWAII2 RG x 2 |
| Gain | 2.99 e-/ADU at YJ-band detector 2.78 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 | ~12 e- (10min. exposure) |
| Linearity | 10% linearity error at 30,000 ADU |
| FIM acquisition CCD pixel scale | 0.067 arcsec/pixel |
| Optics wavelength coverage | 0.97-1.75 um |
| Fiber FoV | 0".48 |
| FIM acquisition CCD camera limiting magnitude |
J = 18.8 (S/N = 10, DIT = 10 sec, in case of a star not injected into a fiber) J = 14.9 (S/N = 10, DIT = 60 sec, in case of a star light injected in to a fiber) If you want to achieve high instrumental RV stability (~2 m/s), we recommend a target with J < 13 mag for a good image centering against a fiber core. |
| FIM acquisition CCD camera wavelength coverage | 0.97-1.1 um |
| FIM acquisition CCD camera FoV | 30" diameter |
| Requirement for a AO guide star | If a star R' mag is brighter than 13, a fiber injection efficiency (FIE) 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 | 1040-1750 nm |
| Mode spacing | 12.5 GHz |
| Frequnecy stability | 0.03 MHz (Standard deviation) for 140 hrs |
| Contrast | >20 dB |
| Intensity stability | 0.7 dB |
| Additional componets | Spectrum shaper, Depolarizer, Mode scramber |
| Method | Simultaneous wavelength reference |
| Fiber | Two multi-mode fibers |
| Calibration sources | Laser comb, ThAr Hollow Cathode Lamp, UrNe lamp |
| Scramblers | Various (not necessary for users to specify) |
| RV instrument stability | ~2 m/s in a short term ~ 1 week (the goal is 1m/s, and the stability demonstration is still ongoing for further improvement. Shared-risk operation still in S2019B) |
| Min. exposure time | 1.5 sec. |
| Typical overhead time | <600 sec. (if your target is faint, overhead will be increased) |
| Sensitivity calculation | Check this page |
| Data reduction | to be updated |