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

Abstract

We investigated if signatures of coronal mass ejections (CMEs) can be retrieved in the differential emission measure (DEM) from Sun-as-a-star extreme-ultraviolet (EUV) observations. We analyzed 16 major, 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 SDO/AIA mission in EUV channels centered at 94, 131, 171, 193, 211, and 335 Angstrom. We also corrected the light curves for the flare gradual phase. From the analysis of the 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 Angstrom channels. The dimmings in these channels become more pronounced upon applying the gradual-phase correction. Calculation of the DEM from the six 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 range $10^{5.7}-10^{6.0}$ K for the DEMs calculated with the original light curves, and in the range $10^{6.0}-10^{6.3}$ K for the DEMs calculated by taking into account the gradual-phase correction. For a sample event, we also calculated DEMs from EVE and spatially resolved AIA observations of the source region 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 is similar for the EVE and larger for the spatially resolved AIA observations. Coronal dimmings associated with CMEs can be detected in Sun-as-a-star DEMs. The flare gradual phase can lead to an underestimation of the magnitude of the dimming.

Figures (7)

• Figure 1: Left: Source AR of the eruptive flare of the fifth event in Table \ref{['table_of_events']} (red box) in a 171 Å image. Right panel: Detected dimmings from the Solar Demon database (in white) in an almost cotemporal 211 Å channel image.
• Figure 2: Sun-as-a-star light curves for the 94, 131, 171, 193, 211, and 335 Å channels of AIA for event 5 in Table \ref{['table_of_events']}). The blue lines are the original light curves, the dashed orange lines are smoothed, and the red lines are corrected. The red-, green-, and blue-shaded vertical boxes correspond to the pre-event, dimming window (for the original light curves), and dimming window (for the corrected light curves), respectively. For this event the correction worked as intended.
• Figure 3: Boxplots of $d_{dimming}$. The left panel has boxplots of $d_{dimming}$ from the uncorrected light curves. The right panel has boxplots $d_{dimming}$ from the corrected light curves
• Figure 4: DEM as a function of temperature for the event in Fig. \ref{['fig:light_curves_corr']}. The red circles indicate the DEMs of the pre-event window, green circles indicate the DEMs of the dimming window made by using the uncorrected light curves, and the blue circles indicate the dimming window made by using the corrected light curves. The respective error bars were calculated via error propagation of the input intensities.
• Figure 5: Boxplots of $d_{\text{DEM}}^{\text{dimming}}$. The left panel has boxplots of $d_{\text{DEM}}^{\text{dimming}}$ calculated by the uncorrected light curves. The right panel has boxplots $d_{\text{DEM}}^{\text{dimming}}$ calculated by the corrected light curves