Physics of the sun outer atmosphere

Owing to its closeness to Earth, the Sun is the most important star for us and the only one we can observe in detail. It can thus act as a precious laboratory revealing the processes taking place in a star, and also as a model allowing us to understand how the other stars work.

The Observatory of Palermo is involved in research activities – dating back to Vaiana’s pioneering work in the 60-70s – which study the X- and EUV- rays coming from the Sun. Satellite observations have shown that the Sun appears more structured and dynamic in the X-ray band than in the optical one. This band allows the observation of the solar corona, made up of plasma millions of degrees hot and strongly influenced by magnetic fields. The plasma trapped inside the corona, being powered by the magnetic field, becomes incandescent and glowing in areas known as coronal arches. The detailed mechanisms behind this process are under study, and might be strictly connected to the fine structure of the corona. When observed at high resolution, coronal arches appear to be formed by bundles of very thin threads and this might reveal the heating of plasma due to the occurrence of frequent and strictly localized small explosions (flares).sun_active_region_true

Astronomers at the Observatory carry out research on the Sun based on observations made during solar missions dating back to the 70s, such as Skylab, Solar Maximum Mission, the European-US SoHO, the Japanese-US Yohkoh and Hinode and the US TRACE and the recent Solar Dynamics Observatory (SDO). The studies concern the structure, evolution and dynamics of the plasma both confined in coronal arches, and erupted out of confinement, and are based not only on data analysis but also on the comparison with detailed physical models requiring complex numerical codes and high performances calculation systems. Recently, a solar eruption observed with SDO has been taken as a template and laboratory to study accretion in forming stars (Science, 2013).

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