New German Instrument Launched at World's Largest Solar Telescope

A groundbreaking instrument developed in Germany has commenced operations at the largest solar telescope on Earth, capturing detailed images of the Sun. The Visible Tunable Filtergraph (VTF) is part of the Daniel K. Inouye Solar Telescope located on the island of Maui, Hawaii.

Constructed by the Leibniz Institute for Solar Physics (KIS) in Freiburg, the VTF aims to provide images of the Sun with unparalleled spatial, temporal, and spectral resolution. The Max Planck Institute for Solar System Research (MPS), based in Göttingen, is a collaborative partner in this significant project.

Weighing in at 5.6 tons and occupying the footprint of a small garage, the VTF is currently the largest spectro-polarimeter in existence. Its development spanned approximately 15 years, with installation at the Daniel K. Inouye Solar Telescope (DKIST) beginning last year.

The VTF utilizes two state-of-the-art Fabry-Pérot interferometers, which are unique in size and precision, to filter narrow wavelength bands from visible sunlight. This technology allows for a spectral resolution that can isolate wavelengths with precision measured in picometers.

For each wavelength and polarization state, the VTF produces two-dimensional images of the Sun, enabling researchers to analyze the temperature, pressure, flow velocity of solar plasma, and the strength of magnetic fields at the solar surface and in the overlying gas layers. The spatial resolution is approximately 10 kilometers per pixel, with the capability to capture several hundred images per second.

This advanced instrument allows scientists to observe the regions of the Sun where solar eruptions originate, specifically the visible surface known as the photosphere and the chromosphere, the layer of the solar atmosphere above it. By examining the interactions between hot plasma flows and dynamic magnetic fields, researchers hope to gain deeper insights into the mechanisms that trigger solar eruptions.

According to Sami Solanki, director of the Sun and Heliosphere department at the MPS, the VTF heralds a new era in ground-based solar observations, offering image quality previously unattainable.

The DKIST, named after a former senator from Hawaii, features a primary mirror measuring four meters in diameter, making it the largest solar telescope currently in operation. The telescope began testing in late 2019 and has been fully operational since 2022. To enhance solar observation capabilities, additional instruments will be gradually integrated into the DKIST to process incoming light, analyzing specific wavelength ranges and vibration directions. The VTF is the fourth and penultimate instrument set for installation.

While the VTF is still undergoing testing, early images reveal minute structures on the solar surface. Once fully operational in a scientific capacity, the data collected will undergo further processing to achieve even higher resolutions.