Aims. We introduce the Chromospheric Telescope (ChroTel) at the Observatorio del Teide in Izaña on Tenerife as a new multiwavelength imaging telescope for full-disk synoptic observations of the solar chromosphere. We describe the design of the instrument and summarize its performance during the first one and a half years of operation. We present a method to derive line-of-sight velocity maps of the full solar disk from filtergrams taken in and near the He i infrared line at 10 830 Å. Methods. ChroTel observations are conducted using Lyot-type filters for the chromospheric lines of Ca ii K, Hα, and He i 10 830 Å. The instrument operates autonomically and gathers imaging data in all three channels with a cadence of down to one minute. The use of a tunable filter for the He i line allows us to determine line-shifts by calibrating the line-of-sight velocity maps derived from the filtergram intensities with spectrographic data from the Tenerife Infrared Polarimeter at high spatial and spectral resolution. Results. The robotic operation and automated data reduction have proven to operate reliably in the first one and and half years. The achieved spatial resolution of the data is close to the theoretical limit of 2 arcsec in Hα and Ca ii K and 3 arcsec in He i. Line-of-sight velocities in He i can be determined with a precision of better than 3-4 km s −1 when co-temporal spectrographic maps are available for calibration. Conclusions. ChroTel offers a unique combination of imaging in the most important chromospheric lines, along with the possibility to determine line-of-sight velocities in one of the lines. This is of interest for scientific investigations of large-scale structures in the solar chromosphere, as well as for context imaging of high-resolution solar observations.
The 1.5 m telescope GREGOR opens a new window to the understanding of solar small-scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro-polarimeter for the visible wavelength range, the GRating Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150 . GREGOR is equipped with a high-order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro-polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness.
The Sunrise balloon-borne solar observatory, consisting of a 1 m aperture telescope that provided a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in June 2013. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg ii k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000Å after Multi-Frame Blind Deconvolution reconstruction accounting for phase-diversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR 11768 observed relatively close to disk centre is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500 G and, while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere.
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