On-Orbit Sensitivity Evolution of the EUV Imaging Spectrometer on Hinode

TL;DR

This paper analyzes the long-term sensitivity decay of the EUV Imaging Spectrometer on Hinode, revealing an exponential decay with a 20-year time constant and solar-cycle effects in high-temperature emission lines.

Contribution

It provides a detailed characterization of the instrument's sensitivity decay over several years using specific emission lines, including the decay rate and solar-cycle influences.

Findings

Sensitivity decays exponentially with a 20-year time constant.

High-temperature emission lines show solar-cycle variations.

Instrument sensitivity decline can be modeled for calibration purposes.

Abstract

Since its launch on 22 September 2006, the EUV Imaging Spectrometer onboard the Hinode satellite has exhibited a gradual decay in sensitivity. Using spectroheliograms taken in the Fe VIII 185.21 Angstrom and Si VII 275.35 Angstrom emission lines in quiet regions near Sun center we characterize that decay. For the period from December 2006 to March 2012, the decline in the sensitivity can be characterized as an exponential decay with an average time constant of 7358 +/- 1030 days (20.2 +/- 2.8 years). Emission lines formed at temperatures >10^6.1 K in the quiet-Sun data exhibit solar-cycle effects.