Signatures of coronal mass ejections in differential emission measure analysis of the Sun as a star

¹ Department of Physics, National and Kapodistrian University of Athens, University Campus, Zografos, GR-157 84 Athens, Greece
² Research Center for Astronomy and Applied Mathematics, Academy of Athens, Soranou Efesiou Str., 4, 11527 Athens, Greece
³ Physics Department, University of Ioannina, Ioannina GR-45110, Greece

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 16 August 2025
Accepted: 25 February 2026

Abstract

Aims. For this work we investigated whether signatures of coronal mass ejections (CMEs) can be retrieved in the differential emission measure (DEM) resulting from extreme-ultraviolet (EUV) observations of the Sun as a star.

Methods. We analyzed a set of 16 major (above the M1.0 class of the Geostationary Operational Environmental Satellites classification), eruptive (i.e., associated with CMEs) flares. For each flare we constructed light curves of the average intensity of full-disk images taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) mission in EUV channels centered at 94, 131, 171, 193, 211, and 335 Å. The light curves comprise both the pre-flare and post-flare phases of the associated flares. We also corrected the light curves for the gradual phase of the associated flare.

Results. From the analysis of the full-disk light curves we find that all the studied flares exhibit dimmings, where the intensity decreases with respect to the pre-flare phase, mainly in the 171, 193, and 211 Å channels. The dimmings in these channels become more pronounced upon applying the gradual-phase correction. Calculation of the DEM from the intensities of the six employed AIA EUV channels shows that during all the observed dimmings, the DEM decreases with respect to its value in the pre-flare phase in the temperature range ≈10^5.7 − 10^6.3 K. The signature of the dimming is more pronounced in the temperature range of ≈10^5.7 − 10^6.0 K for the DEMs calculated with the original light curves, and in the range of ≈10^6.0 − 10^6.3 K for the DEMs that were calculated by taking into account the gradual-phase correction. For a sample event of our database, we also calculated DEMs from EVE and spatially resolved AIA observations of the source region of the corresponding dimming in order to assess the impact of spectral resolution and full-disk averaging. For both these cases the temperature range where the dimming in the DEM is more pronounced is similar to that resulting from the analysis of the spatially averaged AIA data; the magnitude of the dimming in the DEM is similar for the EVE and larger for the spatially resolved AIA observations compared to the Sun-as-a-star AIA observations, respectively.

Conclusions. Coronal dimmings associated with CMEs can be detected in Sun-as-a-star DEMs derived from EUV observations. The gradual phase of the associated flare can lead to an underestimation of the magnitude of the dimming in the intensities and in the DEMs. The application of the correction alters the temperature range in which the signature of the dimming in the respective DEMs is more pronounced.