Measuring relative abundances with SPICE, the EUV spectrometer on board Solar Orbiter

Linking solar activity on the surface and in the corona to the inner heliosphere is one of the main goals of Solar Orbiter. Its unique combination of in-situ and remote sensing instruments can be used to shed light on this difficult task by, e.g., determining the source region of the solar wind measured in-situ at the spacecraft position. A key element in this are data on the elemental composition. Indeed, different structures on the Sun have different abundances as a consequence of the FIP (First Ionization Potential) effect. Comparing in-situ and remote sensing composition data, coupled with modeling, will allow us to trace back the source of heliospheric plasma. We have developed a new method to measure relative abundances of the solar corona using UV spectroscopy. This method does not require a Differential Emission Measure inversion which would require information on a large number of spectral lines and thus high telemetry rates not always available. Instead our method is based on optimized linear combinations of only a few spectral lines which is telemetry efficient but still reliable. We present some examples of abundance diagnostics that can be applied to data from SPICE (SPectral Imaging of the Coronal Environment), the EUV spectrometer on board Solar Orbiter.