Exposure time calculator for Immersion Grating Infrared Spectrograph: IGRINS

Abstract

We present an exposure-time calculator (ETC) for the Immersion Grating Infrared Spectrograph (IGRINS). The signal and noise values are calculated by taking into account the telluric background emission and absorption, the emission and transmission of the telescope and instrument optics, and the dark current and read noise of the infrared detector arrays. For the atmospheric transmission, we apply models based on the amount of precipitable water vapor along the line of sight to the target. The ETC produces the expected signal-to-noise ratio (S/N) for each resolution element, given the exposure-time and number of exposures. In this paper, we compare the simulated continuum S/N for the early-type star HD 124683 and the late-type star GSS 32, and the simulated emission line S/N for the H 2 rovibrational transitions from the Iris Nebula NGC 7023 with the observed IGRINS spectra. The simulated S/N from the ETC is overestimated by 40−50% for the sample continuum targets.

An Exposure Meter of Lijiang Fiber-fed High-Resolution Spectrograph

“…Most instruments use ETC to estimate exposure time, although it has some uncertainties. The simulated S/N from the ETC is overestimated by 40%-50% on IGRINS (Le et al 2015), while it is within 10% for HARPS (ESO 2021).…”

Maunakea Spectroscopic Explorer exposure time calculator for end-to-end simulator: to optimizing spectrograph design and observing simulation

“…The OH emission line data is generated by slightly modifying the OH sky line data for the H band of the IGRINS ETC (i.e., reconvolving the spectra to different resolutions). 11 The wavelengths of the OH emission lines are from Ref. 12, and the calibrated intensity values are from Ref.…”

“…The OH line is so bright that it could be scattered inside the instrument and increase the photon counts in the overall detector area. 11 These considerations are not included in this work. For the optical wavelength range, especially the blue band, the dominant contributor of the optical sky background is the scattered moonlight in the Earth's atmosphere.…”

TARdYS: Design and prototype of an exoplanet hunter for TAO using a R6 Echelle grating

“…12. The detail of simulation method has been presented in [30]. Our throughput parameters used for this simulation are shown in table 3.…”

“…In this simulation, we assume the telescope size of 6.5 m, thoughput of 10 %, readout noise of 5 electrons (for IR array), and dark current of 0.02 electron/s. [30] 0.80 *FRD = fiber focal ratio degradation Fig. 12 Simulation of the signal to noise per resolution element of TARdYS while targeting an M type star.…”