High sensitivity magnetic field measurements with GRIS/GREGOR

With the Grating Infrared Spectropolarimeter (GRIS) at the GREGOR telescope on Tenerife weak magnetic fields in quiet-Sun areas could be measured with unprecedented sensitivity. With a spatial resolution of 0.4 arcsec (≈250 km on the solar surface) a new record for observations in the 1.56μm Fe I lines was achieved, a spectral region with 3 times the magnetic sensitivity than for observations at visible wavelengths.

The continuum image (left) shows the typical pattern in the quiet Sun: bright (hot) granules are surrounded by dark (cool) lanes. The magnetic fields are shuffled around by convective motions and concentrate in these dark lanes. Here the field is highly inclined to the solar surface (i.e., low inclination angles), whereas the magnetic field in the center of the granules is mainly horizontal (close to 90 degrees inclination).

GRIS allows the characterization of these weak magnetic fields (magnetic flux below 250 Gauss, central panel) with unprecedented sensitivity at this spatial resolution.