SDI POL

We introduce a new solar feed for the PEPSI night-time spectrograph of the LBT. It enables spectroscopy of the Sun-as-a-star in circular polarization (CP) and in linear polarization (LP) with a spectral resolution of 250,000 (600ms) for the wavelength range 383-907nm. The polarimeter is a dual-beam design with a modified Wollaston prism as beam splitter and linear polarizer combined with a retractable super-achromatic quarter-wave retarder. The Wollaston beam diameter is 14mm and large enough that it does not require a classical telescopic feed anymore. Both polarimetric beams are reimaged into respective integration spheres from which two fibers feed the scrambled light to the spectrograph. The system is fully automated in the sense that it finds the Sun in the morning, closes the guider loop, observes a predefined number of individual spectra, and moves to a home position at the end of the day. Among the scientific aims is Zeeman-Doppler imaging of the Sun as a star over the next activity cycle. Our first light application detects a clear Stokes-V/I profile with a full amplitude of 1e-4 suggesting a solar disk averaged line-of-sight net magnetic field of +0.37±0.02G, corresponding to an unsigned solar-surface mean magnetic field of 13G.