# Imaging and spectroscopic observations of extreme-ultraviolet brightenings using EUI and SPICE on board Solar Orbiter

**Authors:** Ziwen Huang, L. Teriaca, R. Aznar Cuadrado, L. P. Chitta, S. Mandal, H. Peter, U. Schühle, S. K. Solanki, F. Auchère, D. Berghmans, É. Buchlin, M. Carlsson, A. Fludra, T. Fredvik, A. Giunta, T. Grundy, D. Hassler, S. Parenti, F. Plaschke  
**arXiv:** [2303.15979](https://arxiv.org/abs/2303.15979)  
**Date:** 2023-03-28  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2303.15979v1/

## Key points

- The High Resolution EUV telescope (HRIEUV) on board Solar Orbiter has discovered the smallest extreme-ultraviolet (EUV) brightening events, known as campfires.
- These events were detected using HRIEUV's broad bandpass centered at 17.4 nm, dominated by Fe ix and Fe x emission at about 1 MK.
- Spectral Imaging of the Coronal Environment (SPICE) was used to study the thermal properties of these EUI brightening events.
- Three EUI brightenings were identified in HRIEUV data within small areas covered by the slit of SPICE's EUV spectrometer.
- Line intensities of spectral profiles were obtained through Gaussian fitting to study the evolution of these events over time at different line-formation temperatures.
- Two longer-lived EUI brightenings were observed up to Ne viii temperatures (0.6 MK), while all events were detectable in O vi (0.3 MK).
- In one case, two peaks in intensity light curves for C iii and O vi TR lines were observed, separated by 2.7 minutes and 1.2 minutes respectively, while Ne viii intensity showed a single peak between them.
- Some barely reached coronal temperatures despite being classified as EUV brightening events.
- This study provides new insights into understanding solar activity and its impact on space weather forecasting efforts using advanced instrumentation aboard Solar Orbiter.

## Summary

The High Resolution EUV telescope (HRIEUV) on board Solar Orbiter has recently discovered the smallest extreme-ultraviolet (EUV) brightening events, known as campfires. These events were detected using HRIEUV's broad bandpass centered at 17.4 nm, which is dominated by Fe ix and Fe x emission at about 1 MK. To study the thermal properties of these EUI brightening events, the Spectral Imaging of the Coronal Environment (SPICE) also on board Solar Orbiter was used to simultaneously observe their responses at different wavelengths along with imaging data from EUI. The study focused on three EUI brightenings that were identified in HRIEUV data within small areas covered by the slit of SPICE's EUV spectrometer. Line intensities of spectral profiles were obtained through Gaussian fitting to study the evolution of these events over time at different line-formation temperatures. The results showed that detection of these EUI brightenings was at the limit of SPICE capabilities and could not have been independently identified without aid from HRIEUV observations. Two longer-lived EUI brightenings were observed up to Ne viii temperatures (0.6 MK), while all events were detectable in O vi (0.3 MK), and two longer-lived events were also detected in other transition region lines. In one case, two peaks in intensity light curves for C iii and O vi TR lines were observed, separated by 2.7 minutes and 1.2 minutes respectively, while Ne viii intensity showed a single peak between them. Spectral data from SPICE allowed for following thermal properties of EUI brightenings, indicating that some barely reached coronal temperatures despite being classified as EUV brightening events. Overall, this study provides new insights into understanding solar activity and its impact on space weather forecasting efforts using advanced instrumentation aboard Solar Orbiter.