Coronal bright point statistics

II. Magnetic polarities and mini loops

¹ Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
² Space Research Institute, Austrian Academy of Sciences, Graz, Austria
³ European Space Research and Technology Center, 2200 AG Noordwijk, The Netherlands
⁴ Iceye Oy, Maarintie 6, 02150 Espoo, Finland

^⋆ Corresponding authors; Isabella.Kraus@uni-graz.at; Philippe.Bourdin@uni-graz.at

Received: 13 November 2024
Accepted: 8 January 2025

Abstract

Context. The solar corona maintains temperatures of a million Kelvin or more. The plasma heating mechanisms responsible for these extreme temperatures are still unclear. Large regions of magnetic activity in the photosphere cause extreme ultraviolet (EUV) emission in the corona. Even smaller regions with bipolar and multipolar magnetic fields can generate coronal bright points (CBPs).

Aims. We performed a statistical analysis of 346 CBPs. We used Solar Dynamics Observatory (SDO) images to track CBPs on a continuous basis. Therefore, we were able to collect a database of information on the CPB’s lifetime, shape, polarity, flux emergence, and merging behavior, as well as their magnetic evolution, using the SDO Helioseismic and Magnetic Imager (SDO-HMI) instrument.

Methods. We searched the SDO data archive for the longest continuous interval of uninterrupted observations in 2015. The longest such interval contains 12 consecutive days of full-disk images from the EUV channels of the SDO-AIA instrument. To analyze the properties of CBPs, we employed an automated tracking algorithm to follow the evolution of the CBPs. Furthermore, we manually checked the shape, underlying magnetic polarities, and merging behavior of each CBP.

Results. We provide statistics on the magnetic polarity, emergence, and merging of CBPs. We established a relationship between the CBP’s merging behavior and both its shape and magnetic polarities. Brighter CBPs are visible in all SDO-AIA channels and exhibit strong radiative energy losses. The category of CBPs with a bipolar field has the highest probability of being emissive in all SDO-AIA channels. The majority of CBPs have two opposite polarities below them.

Conclusions. The merging of two CBPs is an unusual phenomenon that is related to complex multipolar magnetic regions. Moreover, loop-shaped CBPs usually appear above bipolar fields. Faint CBPs have shorter lifetimes and are less likely to merge with another CBP.