The GREGOR Fabry-P\'erot Interferometer and its companion the Blue Imaging Solar Spectrometer

TL;DR

The GREGOR Fabry-Pérot Interferometer (GFPI) is a high-resolution, tunable instrument on the GREGOR solar telescope enabling detailed imaging and spectropolarimetry of the Sun's surface, with plans to expand into blue spectral observations.

Contribution

This paper introduces the GFPI's design, capabilities, and initial results, and discusses plans for integrating the Blue Imaging Solar Spectrometer for broader spectral coverage.

Findings

High spectral resolution R ~ 250,000 achieved

Successful initial observations of solar features

Enhanced optical design and automated calibration procedures

Abstract

The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and post-factum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic Sun and its magnetic field at spatial scales down to about 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectrometric and spectropolarimetric observations between 530-860 nm and 580-660 nm, respectively, and possesses a theoretical spectral resolution R of about 250,000. Large-format, high-cadence CCD detectors with sophisticated computer hard- and software enable the scanning of spectral lines in time-spans equivalent to the evolution time of solar features. The field-of-view (FOV) of 50" x 38" covers a significant fraction of the typical area of active regions in the spectroscopic mode. In case of Stokes-vector spectropolarimetry, the FOV reduces to 25" x 38". We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer (BLISS), which will explore the blue spectral region below 530 nm.