GREGOR: The Sun in High Resolution

GREGOR is the largest European Solar Telescope and recent enhancements in optics have allowed us to observe the Sun in extremely high resolution. The images show two snapshots, taken in August 2018 and the size of the Earth for comparison.

The left image shows granulation, hot (~6000 deg) bubbles of gas that are constantly rising and cooling. One granule is nearly as large as Europe. GREGOR allows us to also see the structure of the magnetic field between granules, which is visible as bright tangled features in the images.

The right image shows a sunspot with its detailed fine-structure. The black part is the coolest region (~4500 deg) where the magnetic field is strongest. This sunspot showed an interesting distribution of the penumbra, the filamentary structure surrounding it, which in this case was not symmetric and even protruded into the umbra. This is interesting to scientists because it will allow us to study sunspot evolution and decay, which may influence sunspot eruptions and those can influence Earth, e.g. as Auroras. Sunspots can easily exceed Earth’s size.

GREGOR has experienced significant changes in the past year: Its secondary mirror was replaced, which improved the image contrast significantly. New instrumentation led to faster and better images and data. The adaptive optics algorithms were enhanced and now the adaptive optics lock perfectly even on targets with lower contrast, such as granulation. Sources of vibrations, for example coolers, were identified and solved. By repainting the building and the roof tiles with special paint, which does not heat up, we could reduce the turbulence due to hot air, which leads to sharper images.

Image credit: the images were taken during the international campaign of E. Lastufka (FHNW), B. Panos (FHNW), L. Kleint (KIS) using the HIFI instrument (AIP) with a G-band filter and speckle-reconstructed using the KISIP code.