Spatially resolved Stokes measurements in the Sr I (4607.3 Å) line with FSP at VTT/TESOS

F. ZEUNER; FELLER, ALEX; IGLESIAS, FRANCISCO A.; MILIC, IVAN

Lanzarote

Conferencia; SOLARNET IV MEETING; 2017

SOLARNET, European Union

Scattering polarization signals at spatial scales in the 0.1"-1" regime are a very promising complementary diagnostic for theSun's atmosphere and magnetism at small spatial scales. So far, forthe Sr I line at 4607.3 Å, which exhibits a large scatteringpolarization signal, only theoretical predictions for the strength andspatial distribution of linear polarization signals at sub-arcsecondscales are available, whereas observational feedback has beenmissing. Here, we present results of two VTT/TESOS campaigns inMay 2015 and June 2014. In May 2015, we measured the center-tolimbvariation of the spatially averaged Stokes Q profiles to test theability to measure scattering polarization using the prototype of theFast Solar Polarimeter. To obtain the spatial distribution of theStokes vector, we have observed the Sr I line in the quiet Sun atμ=0.6 from the north solar limb in June 2014, with a spatialsampling of 0.08" and noise levels as low as 0.6% per pixel forlinearly polarized signals with 1.25 s integration time. To obtain thetheoretically required lower noise levels (< 0.1%), while conservingsufficient spatial resolution to resolve the solar granulation, wecarefully performed spatial and temporal averaging. Our analysis ofthe images indicates a strong correlation of the line core Stokes Qsignals with the intensity of the nearby continuum.