Optical design of the COSMO large coronagraph

The Coronal Solar Magnetism Observatory (COSMO) is a facility dedicated to measuring magnetic fields in the corona and chromosphere of the Sun. It will be located on a mountaintop in the Hawaiian Islands and will replace the current Mauna Loa Solar Observatory (MLSO). COSMO will employ a suite of instruments to determine the magnetic field and plasma conditions in the solar atmosphere and will enhance the value of data collected by other observatories on the ground (SOLIS, ATST, FASR) and in space (SDO, Hinode, SOHO, GOES, STEREO, DSCOVR, Solar Probe+, Solar Orbiter). The dynamics and energy flow in the corona are dominated by magnetic fields. To understand the formation of Coronal Mass Ejections (CMEs), their relation to other forms of solar activity, and their progression out into the solar wind requires measurements of coronal magnetic fields. The COSMO suite includes the Large Coronagraph (LC), the Chromosphere and Prominence Magnetometer (ChroMag) and the K-Coronagraph. The Large Coronagraph will employ a 1.5 meter fuse silica singlet lens and birefringent filters to measure magnetic fields out to two solar radii. It will observe over a wide range of wavelengths from 500 to 1100 nm providing the capability of observing a number of coronal, chromospheric, and photospheric emission lines. Of particular importance to measuring coronal magnetic fields are the forbidden emission lines of Fe XIII at 1074.7 nm and 1079.8 nm. These lines are faint and require the very large aperture. NCAR and NSF have provided funding to bring the COSMO Large Coronagraph to a preliminary design review (PDR) state by the end of 2013.