GREGOR Fabry-Perot Interferometer - status report and prospects

TL;DR

The GREGOR Fabry-Perot Interferometer (GFPI) is a high-resolution, tunable instrument on the GREGOR solar telescope enabling detailed spectropolarimetric imaging of the Sun's surface at small spatial scales.

Contribution

This paper reports on the current status, technical characteristics, and initial observational results of the GFPI, including design improvements and future plans for a second FPI for blue spectral observations.

Findings

Successful implementation of a high-resolution spectropolarimetric instrument

First observational results demonstrating instrument capabilities

Plans for integrating a second FPI for blue spectral range

Abstract

The GREGOR Fabry-Perot 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 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530-860 nm with a theoretical spectral resolution of R ~ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful 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 of 50" x 38" covers a significant fraction of the typical area of active regions. 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, which will explore the blue spectral region below 530 nm.