The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-m GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and postfactum 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 spectrometric and spectropolarimetric observations between 530–860 nm and 580–660 nm, respectively, and possesses a theoretical spectral resolution of R≈250,000. Large-format, high-cadence charged coupled device 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″×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″×38″. The main characteristics of the GFPI including advanced and automated calibration and observing procedures are presented. Improvements in the optical design of the instrument are discussed and first observational results are shown. Finally, the first concrete ideas for the integration of a second FPI, the blue imaging solar spectrometer, are laid out, which will explore the blue spectral region below 530 nm.
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 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′′×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.
An image stabilization system has been developed and demonstrated for solar observations in the visible wave-length at Udaipur Solar Observatory (USO) with a 15 cm Coudé-refractor. The softwa4re and hardware components of the system are similar to that of the low cost solar adaptive optics system developed for the 1.5 m McMath-Pierce solar telescope at Kitt Peak observatory for solar observations in the infrared. The first results presented. The system has a closed loop correction bandwidth in the range of 70 to 100 Hz. The root mean by a factor of 10 to 20. The software developes and key issues concerning optimum system performance have been addressed.
A Multi-Application Solar Telescope (MAST) is proposed to be installed at the Udaipur Solar Observatory (USO)
in India to monitor the Sun in optical and near infra-red wavelengths. The median value of the Fried's parameter
at this site is 4 cm. USO is in the process of building an Adaptive optics (AO) system in order to have diffraction
limited performance of the MAST under this moderate seeing condition. AO helps in achieving high-resolution
imaging by compensating the atmospheric turbulence in real-time. We have performed simulations to evaluate
the performance of AO for various seeing conditions. It was concluded that with the present availability of AO
system components, a 55 cm aperture telescope would yield optimum performance with AO, in combination with
post-processing techniques like speckle imaging and phase diversity. At present, we are developing a proto-type
AO system at USO to demonstrate its performance with a 15 cm Coude´ refracting telescope as a preparation for
the main AO system to be deployed on the MAST. The prototype AO system is being realized in two phases.
In the first phase, we have developed an image stabilization system to compensate the global tilt of the wave-front.
The second phase consists of sensing and correcting the local tilts of the wave-front by integrating a
micro-machined membrane deformable mirror with the image stabilization system and is currently in progress.
Here, we present the details of our proto-type AO system. We also present preliminary results obtained from
simulations using Phase Diversity as a post processing technique.
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