Revised Wavelength and Spectral Response Calibrations for AKARI Near-Infrared Grism Spectroscopy: Post-Cryogenic Phase

TL;DR

This paper provides revised wavelength and spectral response calibrations for AKARI's near-infrared grism spectroscopy during its post-cryogenic phase, accounting for temperature variations and second-order light contamination.

Contribution

It introduces updated calibration methods for the post-cryogenic phase, including temperature-dependent response correction and second-order contamination assessment.

Findings

Response decreased by ~10% with temperature increase.

Wavelength calibration curves remained consistent across sub-phases.

Second-order light contamination was 25% smaller than in earlier phases.

Abstract

We present a new calibration for the second-order light contamination in the near-infrared grism spectroscopy with the Infrared Camera aboard AKARI, specifically for the post-cryogenic phase of the satellite (Phase 3). Following our previous work on the cryogenic phase (Phases 1 and 2), the wavelength and spectral response calibrations were revised. Unlike Phases 1 and 2, during Phase 3, the temperature of the instrument was not stable and gradually increased from 40 to 47 K. To assess the effect of the temperature increase, we divided Phase 3 into three sub-phases and performed the calibrations separately. As in Phases 1 and 2, we confirmed that there was contamination due to the wavelength dependence of the refractive index of the grism material in every sub-phase. The wavelength calibration curves for the three sub-phases coincided with each other and did not show any significant temperature dependence. The response decreased with temperature by ~10% from the beginning to the end of Phase 3. We approximated the temperature dependence of the response as a linear relation and derived a correction factor as a function of temperature. The relative fraction of the second-order light contamination to the first-order light was found to be by 25% smaller than in Phases 1 and 2.