Temperature of Solar Orbiter/EUI quiet Sun small scale brightenings: evidence for a cooler component

TL;DR

This study investigates small-scale EUV brightenings in the Quiet Sun observed by Solar Orbiter, revealing evidence for a cooler component and analyzing their thermal evolution to understand their origin and impact on solar atmospheric heating.

Contribution

The paper introduces a thermal analysis method combining Solar Orbiter and SDO data to identify a dominant cool component in small-scale brightenings, advancing understanding of their thermal properties.

Findings

Events show time lags less than 12 seconds across AIA bands.

Evidence suggests coexistence of events reaching coronal temperatures and cooler populations.

Cool population likely dominates the observed brightenings.

Abstract

Context: On 2020 May 30, small and short-lived EUV brightenings were observed in the Quiet Sun (QS) during a four minutes sequence by EUI/HRIEUV on board Solar Orbiter. Their physical origin and possible impact on coronal or Transition Region (TR) heating are still to be determined. Aims: Our aim is to derive the statistical thermal evolution of these events in order to establish their coronal or TR origin. Methods. Our thermal analysis takes advantage of the multithermal sensitivity of the Atmospheric Imaging Assembly (AIA) imager on board the Solar Dynamics Observatory (SDO). We first identified these HRIEUV events in the six coronal bands of AIA. We then performed a statistical time lag analysis, which quantifies the delays between the light curves from different bands. These time lags can give significant insights into the temperature evolution of these events. The analysis is performed taking into account the possible contribution to the results from the background and foreground emissions. Results: The events are characterized by time lags inferior to the AIA cadence of 12 s, for all nine couples of AIA bands analyzed. Our interpretation is the possible co-presence of events which reach or do not reach coronal temperatures ($\approx$ 1MK). We believe that the cool population dominates the events analyzed in this work.