Gregor@night: The future high‐resolution stellar spectrograph for the GREGOR solar telescope

Abstract

We describe the future night-time spectrograph for the GREGOR solar telescope and present its science core projects. The spectrograph provides a 3-pixel resolution of up to R = 87 000 in 45échelle orders covering the wavelength range 390-900 nm with three grating settings. An iodine cell can be used for high-precision radial velocity work in the 500-630 nm range. The operation of the spectrograph and the telescope will be fully automated without the presence of humans during night-time and will be based on the successful STELLA control system. Future upgrades include a second optical camera for even higher spectral resolution, a Stokes-V polarimeter and a link to the laser-frequency comb at the Vacuum Tower Telescope. The night-time core projects are a study of the angular-momentum evolution of "The Sun in Time" and a continuation of our long-term Doppler imaging of active stars.

Preparing the GREGOR solar telescope for night‐time use: Deriving a pointing model

“…It has been shown that the GREGOR solar telescope is capable of unattended night-time operation as required for Gre-gor@night (Strassmeier et al 2012) by assessing its capability to point to any position within the entire reachable sky with remarkable accuracy. Alignment problems of the coudé train are suggested by the results of the pointing campaign, but should be clarified further by measuring the (differential) pointing model at the coudé focus and with the piggy-back telescope simultaneously rather than sequentially.…”

GREGOR Fabry-Pérot interferometer and its companion the blue imaging solar spectrometer

“…The inclusion of a spectrograph for stellar activity studies and the search for solar twins expand the scientific usage of the GREGOR telescope to the nighttime domain. 24 The GREGOR telescope replaced the 45-cm Gregory-Coudé Telescope, which had been operated on Tenerife since 1985. The construction of the new telescope was carried out by a consortium of several German institutes, namely, the Kiepenheuer-Institut für Sonnenphysik Freiburg, the Leibniz-Institut für Astrophysik Potsdam (AIP), and the Institut für Astrophysik Göttingen.…”