A Newly-Coated Primary Mirror for the Blanco Telescope

Tim Abbott and Roberto Tighe, CTIO

The V. M. Blanco 4-m telescope primary mirror was realuminized on 28 June 2018, for the first time since 2011 and subsequent to the installation of DECam in 2012. The resulting surface is excellent, with 25%, 15%, and 10% improvement in the reflectivity in g, r, and i, respectively. While the long period between coatings is not optimal, the reflectivity and scattering have nevertheless been quite stable for several years as a result of our program of CO2 snow cleanings every week and wet washes every 3 months. We have now established a much-improved procedure for telescope disassembly, mirror realuminization, and reassembly, and we anticipate its timely repetition in the future. Further improvements to the thermal control of the primary are now under way.