Fast Solar Polarimeter

FELLER, A.; IGLESIAS, F. A; NAGARAJU, K.; SOLANKI, S.K.

Simposio; IAU Symposium 305: Polarimetry: From the Sun to Stars and Stellar Environments; 2014

International Astronomical Union

We are developing a novel Fast Solar imaging Polarimeter (FSP), with an emphasis on significantly increased polarimetric accuracy in combination with high spatial resolution. FSP is based on a high frame-rate (400 fps), low-noise (< 3 e- RMS), pnCCD camera, and ferroelectric liquid crystals. The fast polarization modulation, yielding up to 100 individually recorded full-Stokes frame sets per second, suppresses spurious polarization signals induced by external disturbances such as atmospheric turbulence or instrument jitter. On the other hand, high-precision polarimetry in the presence of fast solar evolution (1-10s at the targeted spatial resolution) asks for short exposure times allowing for post-facto image reconstruction, and for high throughput and duty cycle, in order to reach a given polarimetric sensitivity in the shortest possible time. The main scientific focus of FSP will be on studies of small-scale magnetic fields in the photosphere, and of highly dynamic chromospheric magnetic structures. The observing regime covered by this instrument also requires novel approaches in data analysis, like feature tracking or feature based averaging, in order to cope with the low photon limited per-pixel signal-to-noise ratios. The FSP development is split in 2 phases. During phase 1 we have developed a prototype based on a small 264 x 264 pnCCD, and tested its performance at the spectrograph and filtergraph instruments of the German Vacuum Tower Telescope on Tenerife. Phase 2, which has started this year with the development of a 1k x 1k pnCCD sensor by the semiconductor lab of the Max Planck society, will lead to the first science-ready version of FSP. We will describe the FSP instrument and present some first results obtained with the prototype.