The history of a quiet-Sun magnetic element revealed by IMaX/SUNRISE

摘要

Isolated flux tubes are considered to be fundamental magnetic building blocksof the solar photosphere. Their formation is usually attributed to theconcentration of magnetic field to kG strengths by the convective collapsemechanism. However, the small size of the magnetic elements in quiet-Sun areashas prevented this scenario from being studied in fully resolved structures.Here we report on the formation and subsequent evolution of one suchphotospheric magnetic flux tube, observed in the quiet Sun with unprecedentedspatial resolution (0\farcs 15 - 0\farcs 18) and high temporal cadence (33 s).The observations were acquired by the Imaging Magnetograph Experiment (IMaX)aboard the \textsc{Sunrise} balloon-borne solar observatory. The equipartitionfield strength magnetic element is the result of the merging of several samepolarity magnetic flux patches, including a footpoint of a previously emergedloop. The magnetic structure is then further intensified to kG field strengthsby convective collapse. The fine structure found within the flux concentrationreveals that the scenario is more complex than can be described by a thin fluxtube model with bright points and downflow plumes being established near theedges of the kG magnetic feature. We also observe a daisy-like alignment ofsurrounding granules and a long-lived inflow towards the magnetic feature.After a subsequent weakening process, the field is again intensified to kGstrengths. The area of the magnetic feature is seen to change in anti-phasewith the field strength, while the brightness of the bright points and thespeed of the downflows varies in phase. We also find a relation between thebrightness of the bright point and the presence of upflows within it.