Short overview of the four SOLARNET campaigns in 2016 at GREGOR

A. Diercke, S.J. González Manrique, M. Verma, M. Sobotka, J. Löhner-Böttcher, H. Balthasar, and C. Denker

The GREGOR Fabry-Perot Interferometer (GFPI) is installed at the 1.5-meter GREGOR telescope on Tenerife, Spain. The coatings of the etalons of the GFPI have a high reflectivity in the wavelength range between 530-860 nm. Therefore, during a 50-day first-science campaign in 2014 the chromospheric Ca II 854.2 nm line was observed with the GFPI in spectroscopic mode. The target was a group of pores close to disk center in active region NOAA 12149 on 2014 August 26. A non-equidistant wavelength spacing to scan through the broad Ca II 854.2 nm line was used. Narrower step sizes were taken close to the line core. Each of the 20 scans comprised 36 steps. Four images with an exposure time of 80 ms were acquired per step. We will present some physical properties of the group of pores derived from the inversions of the Ca II 854.2 nm intensity profiles using the non-LTE radiative transfer code NICOLE. This code is especially useful to infer atmospheric parameters from chromospheric lines formed under non-LTE conditions.

Over the past decades we have discovered that most of the processes on the Sun are coupled across many layers of the atmosphere. For instance, filaments and arch filament systems are best observed in the chromosphere and corona but are rooted in the photosphere. Another example are the changes in the vector magnetic field during flares which are noticeable from the corona down to the photosphere. Furthermore, small magnetic flux emergence has been tracked observationally from the photosphere to the corona. Therefore, it is crucial to have simultaneous observations covering as many atmospheric layers as possible. The next generation of large solar telescopes will focus on the ability to simultaneously observe the Sun in many different wavelengths. Until now, this has been only possible by coordinating different ground and space based telescopes, in order to observe the same area on the Sun with different instruments. In this talk I will present some examples of recent multi-wavelength studies and show how the European Solar Telescope will improve such multi-wavelength observations.

M. Collados

An M3.2 flare was observed in 2013 May 17 with the Vacuum Tower Telescope (VTT, Tenerife, Spain) at a heliocentric angle of 0.8. The observations covered the activation, impulsive, and relaxation phases of the flare. This work is an extension of the already published work from Kuckein et al. (2015, ApJL,799, L25), which was based on photospheric changes during this flare. In this work, we concentrate on the changes in the chromosphere, analyzing the Ca II 8542 line during the M-class flare. Large emission peaks are present during the flare and relaxation phases. Strong asymmetries of the intensity profiles are detected in the red wing during the flare, which indicates strong downflows. Temperatures and velocities were inferred from selected profiles using the inversion code NICOLE. Our results add to the few earlier studies concerning flare observations in the Ca II infrared line. Observing flares from ground-based telescopes is very challenging. Recommendations about instrumentation will be presented including possible strategies for flare observations with the European Solar Telescope (EST) in the chromosphere.