SDI / SDI-POL

Disk-unresolved solar light is fed to the spectrograph from a small Sun-as-a-star telescope via a fibre connection to the calibration unit. In the original instrument, an integration sphere behind the telescope feeds a fiber to the spectrograph. An upgraded version (SDI-POL), currently under construction, will feed polarised light via two fibers to the spectrographin order to obtain time resolved high spectral resolution R =250 000 spectrum of the solar disk in full Stokes IQUV vector in a range 3825–9125Å. Five main aims have been identified:

• Study the dynamics of the solar atmosphere over the entire solar cycle by observing disk integrated line profile variations of temperature and pressure sensitive photospheric lines.
• Study the differential rotation of the Sun with the same techniques applicable to stars.
• Study the net solar magnetic field density variations in different time scales and to verify multipole magnetic field models of the Sun-like stars.
• Study the solar p-mode oscillations by using Stoke I integral light spectra in time resolved mode and the variations of the p-mode oscillation spectrum over time.
• Monitor the point spread function of the spectrograph over time.