Unfolding EIS Slot Data

Slitless spectrometers can provide both imaging and spectral information over a large field of view, however overlapping spectral lines can create spatial/spectral confusion in the dispersion direction. Extreme-ultraviolet Imaging Spectrometer (EIS) instrument on the Hinode satellite can acquire slot data with a 266” slot in either one or both of the wavelength channels creating these “overlapograms.” Slot data around the He II 25.6 nm line is often used as a flare trigger. This wavelength range also includes the Fe XXIV emission line that brightens significantly during a solar flare. Harra et al. (2017) have used a combination of EIS slot data and images from the Atmospheric Imaging Assembly (AIA) to demonstrate the potential velocity signature in the Fe XXIV lines at the flare on-set by using the AIA data to predict the EIS spatial distribution, then interpreting any additional deviations from the predictions as an indication of velocity.

Recently, a method was developed to unfold slitless spectrometer data was tested for the COronal Spectroscopic Imager in the EUV (COSIE) instrument. In this presentation, we show the results of applying this method to a combination of the EIS slot and co-temporal, co-spatial AIA data. We first use simulated EIS and AIA data to determine appropriate spatial, temperature, and velocity resolutions for the inversion. We then apply this method to the flare data shown in Harra et al. (2017). Combining this method with EIS slot data provides a quantitative measure of the velocity observed in Fe XXIV and other spectral lines at the start of a solar flare.