During September to December 2012, the Near Earth Object Survey Telescope of Purple Mountain Observatory recoated the spherical primary mirror in size of 1.2 m, with the support of the astronomical special finance and the renovation and purchase special finance of the Ministry of Finance. On 30 December 2012, the telescope resumed observation, after the recoated mirror had been fixed on the telescope and a preliminary debugging of system.

The primary mirror firstly coated with "Al+SiO" surface in 2004, and the average reflectance was 85% in visible region. Usually this kind of surface need be recoated every 2 years. In 2012, the reflectance decreased to 65% (633 nm wave), and starve for recoating. In September 2012, the mirror was transported to Changchun to recoat by "Al + multilayer dielectric" surface, and was transported back to Xuyi successfully in late December. After this recoat, the optical performance of the mirror matched the new 10k×10k CCD in plan (in Fig. 1). the reflectance of the new surface is better than 96% in the range between 550 nm and 800 nm wave band, and will greatly enhance the performance of the telescope in the observation of solar system objects surveys and anti-Galaxy narrowband surveys.

By with ZHAO Haibin

 

Fig 1 The reflectivity spectrum curve of the new coating of primary mirror of NEOST