26 August 2009 EUVS-C: the measurement of the magnesium II index for GOES-R EXIS
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The EUV and X-ray Irradiance Sensors (EXIS) on the upcoming GOES-R mission will include a spectrograph to measure the Magnesium II doublet at 280 nm (channel C). The ratio of the core of this spectral feature to the line wings is the well-known Mg II index. This ratio is often used as a proxy for chromospheric activity, since changes in the index are highly correlated with changes in other chromospheric emission lines. As a ratio measurement, the Mg II index is relatively insensitive to instrumental effects. The A and B channels of the Extreme UltraViolet Sensor (EUVS) will make use of this fact and use the Mg II index measured by channel C in their degradation correction. EUVS C channel has sufficient spectral resolution and sampling to measure the Mg II index with high precision and will make this measurement at better than 30 s time cadence. This paper describes the design and measurement requirements of the C channel.
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Martin Snow, William E. McClintock, David Crotser, Francis G. Eparvier, "EUVS-C: the measurement of the magnesium II index for GOES-R EXIS", Proc. SPIE 7438, Solar Physics and Space Weather Instrumentation III, 743803 (26 August 2009); doi: 10.1117/12.828566; https://doi.org/10.1117/12.828566

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